How Old School C Programmers Process Arguments(usrsb.in)
usrsb.in
How Old School C Programmers Process Arguments
http://www.usrsb.in/How-Old-School-C-Programmers-Process-Arguments.html
78 comments
> If you need that whole paragraph to understand (* ++argv)[0], you might be an awesome programmer, but you're not yet a reasonably experienced C programmer. ;)
Lines like that have far too much information density for my old brain, anymore.
Things that went through my poor brain: "Why pre-inc/decrement? Why the +1 on the for? Did he actually get the precedence of the operators correct? Okay, it looks like argc and argv will be mangled if you actually want to do anything else with them. I see comparing to '\0' with no count limit--is there a buffer overrun lurking here?. Does that error handling actually work--that loop can't exit with that condition unless the second clause does something.
And that was like--30 seconds?
I'd assign argc and argv to something else so if I need them later for something they are in their original state. I'd give myself a variable that points to each individual argv on each iteration, and I'd call it something. I'd make the error handling more explicit so if I had to add another case later I wouldn't have to rack my brain about whether the error gets handled. Etc.
Apparently I've become an inflexible, washed-up, old fart because I just don't enjoy writing C code with that kind of puzzle-like quality anymore.
Lines like that have far too much information density for my old brain, anymore.
Things that went through my poor brain: "Why pre-inc/decrement? Why the +1 on the for? Did he actually get the precedence of the operators correct? Okay, it looks like argc and argv will be mangled if you actually want to do anything else with them. I see comparing to '\0' with no count limit--is there a buffer overrun lurking here?. Does that error handling actually work--that loop can't exit with that condition unless the second clause does something.
And that was like--30 seconds?
I'd assign argc and argv to something else so if I need them later for something they are in their original state. I'd give myself a variable that points to each individual argv on each iteration, and I'd call it something. I'd make the error handling more explicit so if I had to add another case later I wouldn't have to rack my brain about whether the error gets handled. Etc.
Apparently I've become an inflexible, washed-up, old fart because I just don't enjoy writing C code with that kind of puzzle-like quality anymore.
I feel an upvote is insufficient. An explicit thank you is necessary too.
I agree. This tradition of writing short overly-clever code in C needs to die off. Screens can display more than 80x24 characters these days; we should use them.
i disagree with the sentiment and preferences expressed in your comment. the code on display is at the sweet spot of complexity given the scope of task at hand. your preferences might lead to code with lower complexity of any given expression, but there would be a higher number of expressions, higher number of statements, and higher number of names. that would mean higher complexity of the full code. should we ban multiplication on the basis that X times Y is the same as X plus X plus X...?
> Why pre-inc/decrement?
as opposed to what? nothing? clearly, the code needs to advance the iterators before dereferencing.
> Why the +1 on the for?
because it's interested in the option name as opposed to the leading dash: argv[0][0] is '-' (see the while above), the switch is looking at argv[0][1].
> Did he actually get the precedence of the operators correct?
not sure what this is about, the only involved expression has explicit parentheses (out of necessity).
> Okay, it looks like argc and argv will be mangled if you actually want to do anything else with them.
yes... and? mutating a local int and a local pointer is bad? how would you go about this without mutating an iterator?
> I see comparing to '\0' with no count limit--is there a buffer overrun lurking here?
nope, it's an array of null-terminated strings.
> Does that error handling actually work--that loop can't exit with that condition unless the second clause does something.
i do not understand what you're pointing at here.
> I'd assign argc and argv to something else so if I need them later for something they are in their original state.
consider they're already local names, and YAGNI. do alias them if you need them later, not because you might one day.
> I'd give myself a variable that points to each individual argv on each iteration, and I'd call it something.
you would give yourself a possible bug and an obligation to keep the two things in sync.
> I'd make the error handling more explicit so if I had to add another case later I wouldn't have to rack my brain about whether the error gets handled.
what is more explicit than
i'd really love to see your preferred version of the snippet from TFA. i posit it'd be two to three times as long, and its total complexity would be similarly increased.
> Why pre-inc/decrement?
as opposed to what? nothing? clearly, the code needs to advance the iterators before dereferencing.
> Why the +1 on the for?
because it's interested in the option name as opposed to the leading dash: argv[0][0] is '-' (see the while above), the switch is looking at argv[0][1].
> Did he actually get the precedence of the operators correct?
not sure what this is about, the only involved expression has explicit parentheses (out of necessity).
> Okay, it looks like argc and argv will be mangled if you actually want to do anything else with them.
yes... and? mutating a local int and a local pointer is bad? how would you go about this without mutating an iterator?
> I see comparing to '\0' with no count limit--is there a buffer overrun lurking here?
nope, it's an array of null-terminated strings.
> Does that error handling actually work--that loop can't exit with that condition unless the second clause does something.
i do not understand what you're pointing at here.
> I'd assign argc and argv to something else so if I need them later for something they are in their original state.
consider they're already local names, and YAGNI. do alias them if you need them later, not because you might one day.
> I'd give myself a variable that points to each individual argv on each iteration, and I'd call it something.
you would give yourself a possible bug and an obligation to keep the two things in sync.
> I'd make the error handling more explicit so if I had to add another case later I wouldn't have to rack my brain about whether the error gets handled.
what is more explicit than
printf("Illegal option %c\n", *s);
i'd really love to see your preferred version of the snippet from TFA. i posit it'd be two to three times as long, and its total complexity would be similarly increased.
> Why pre-inc/decrement?
No, why "pre-" instead of "post-"? Is that a real requirement , or is this an old C++ programmer who knows to write pre-crement in order to avoid creating unnecessary copies?
> Did he actually get the precedence of the operators correct?
It's because I see a "chain" of operators and I have to think about it.
> nope, it's an array of null-terminated strings.
Is it? What happens when I pass 256 '-' characters. Or maybe 32767/32768/65535/65536? Or maybe ...
> Does that error handling actually work--that loop can't exit with that condition unless the second clause does something.
If I need to add a second unflagged argument, that error condition test also needs to be updated. It's an annoyance.
A lot of this is no big deal in this code.
The problem is that code is habit. You will carry the habits from short code over to long code. So, when you are now parsing 45 flags and 8 arguments, you will write code the same way and it WILL have bugs.
No, why "pre-" instead of "post-"? Is that a real requirement , or is this an old C++ programmer who knows to write pre-crement in order to avoid creating unnecessary copies?
> Did he actually get the precedence of the operators correct?
It's because I see a "chain" of operators and I have to think about it.
> nope, it's an array of null-terminated strings.
Is it? What happens when I pass 256 '-' characters. Or maybe 32767/32768/65535/65536? Or maybe ...
> Does that error handling actually work--that loop can't exit with that condition unless the second clause does something.
If I need to add a second unflagged argument, that error condition test also needs to be updated. It's an annoyance.
A lot of this is no big deal in this code.
The problem is that code is habit. You will carry the habits from short code over to long code. So, when you are now parsing 45 flags and 8 arguments, you will write code the same way and it WILL have bugs.
I sort-of agree that the code in the article is not really future-expansion-proof, and in fact, it's not really incompetent-programmer-proof. In the enterprise, you'd probably write incompetent-programmer-proof code, even if you're very competent yourself, just to prevent trouble later.
Kernighan and Ritchie did not need to bother with less profient programmers maintaining their code. They wrote what they and their friends understood, and apparently that was this.
So in short, the GP (bsder) does have a point.
Kernighan and Ritchie did not need to bother with less profient programmers maintaining their code. They wrote what they and their friends understood, and apparently that was this.
So in short, the GP (bsder) does have a point.
I am not a C programmer, nor a veteran in any other language and this code was pretty clear.
I can easily understand the code on the article, but other than the "gee look how cool!" factor, I never write such kind of code in production, as I take a few seconds to think about who might have to maintain it.
> I do think this is even more concise than they would have written in maintained code. In particular, I believe the missing {}'s for the 'while' and 'for' loops wouldn't have been left away, but I might be mistaken.
Well it depends a bit. Plan 9 is written very much in this style, but its easy to maintain because it has rules on when to omit things like braces or parens. You learn the rules pretty quickly (or read rob pike's paper) and after reading and using it a bit will make sense and you won't think about it. I would imagine if you just had someone in the group that wrote like this and the rest of you weren't used to it or the rules were applied inconsistently it would be a huge pain to actually deal with. What matters for all styles is that everyone has rules they agree with and actually follow them.
Well it depends a bit. Plan 9 is written very much in this style, but its easy to maintain because it has rules on when to omit things like braces or parens. You learn the rules pretty quickly (or read rob pike's paper) and after reading and using it a bit will make sense and you won't think about it. I would imagine if you just had someone in the group that wrote like this and the rest of you weren't used to it or the rules were applied inconsistently it would be a huge pain to actually deal with. What matters for all styles is that everyone has rules they agree with and actually follow them.
> If you need that whole paragraph to understand (* ++argv)[0], you might be an awesome programmer, but you're not yet a reasonably experienced C programmer. ;)
That's the beauty of C. It can both amaze and terrify you at the same time. It's the programming equivalent of Philippe Petit. It's walking on a tight rope between the twin towers without a parachute or safety net.
If anyone here enjoys awe and terror of C, look through the ioccc submissions.
https://www.ioccc.org/winners.html
That's the beauty of C. It can both amaze and terrify you at the same time. It's the programming equivalent of Philippe Petit. It's walking on a tight rope between the twin towers without a parachute or safety net.
If anyone here enjoys awe and terror of C, look through the ioccc submissions.
https://www.ioccc.org/winners.html
So it will admit any combination of -n and -x. In particular, these things won't raise an error:
find - hello
find - - hello
find -xnxn hello
find -x -n -x hello
find -xxx -nnn -xn hello
In particular, these things won't raise an error
They don't necessarily need to be. Repeating the same option can either have no effect (|), invert the option (^), or increase something (as in -vvvvv.) IMHO it's a good thing when there are no error cases --- it basically means the entire input space has a defined effect.
They don't necessarily need to be. Repeating the same option can either have no effect (|), invert the option (^), or increase something (as in -vvvvv.) IMHO it's a good thing when there are no error cases --- it basically means the entire input space has a defined effect.
Raising an error is an intentionally defined effect.
Doing something under-defined, by accident, that you'll at some point break because you weren't thinking of that specific edge case when e.g. refactoring, for someone else who didn't actually intend to exercise that edge case but never realized they were doing so as they never received an error... well, not my cup of tea.
Doing something under-defined, by accident, that you'll at some point break because you weren't thinking of that specific edge case when e.g. refactoring, for someone else who didn't actually intend to exercise that edge case but never realized they were doing so as they never received an error... well, not my cup of tea.
And causing errors for everything will cause your program to bug out in perfectly valid cases.
Defensive versus total programming. Either have their place, but ...
Thing is most programmers vastly overestimate the case for defensive programming. In practice, most programs need to run. So for instance, the control loop for a nuclear reactor is not defensively programmed. It never, ever, ever gets to yield an error. Why ? Because the system is not "fail-safe". If the program ever were to say "this doesn't make sense, I'm quitting (or otherwise doing nothing)", there is nothing guaranteeing the system is in a safe state, and so it may melt down. A bug that fails to notice a critical condition, and ignores it, on the other hand leaves the system under the control of the operator, and nothing (should) go wrong (meaning the second level checks should catch the problem)
The general guideline is defensive programming when starting up, with a force switch to override it (so the system can be (re)started if operators decide that's the best outcome). Once the program is running, total programming should be your go-to solution. When in doubt, do the best you can and continue on to the next request.
Since I've been programming million qps+ systems, I've learned that there's even nothing wrong with almost totally ignoring errors. You'd be surprised how well the following works: before handling a request, note down the time (using the cheap instruction), then every time you leave your method, check the time. If it's over a timeout, increase a counter, log if not logged in the past 10s, and send an empty reply. This makes the developer's job harder, but makes everybody else a lot happier.
Defensive versus total programming. Either have their place, but ...
Thing is most programmers vastly overestimate the case for defensive programming. In practice, most programs need to run. So for instance, the control loop for a nuclear reactor is not defensively programmed. It never, ever, ever gets to yield an error. Why ? Because the system is not "fail-safe". If the program ever were to say "this doesn't make sense, I'm quitting (or otherwise doing nothing)", there is nothing guaranteeing the system is in a safe state, and so it may melt down. A bug that fails to notice a critical condition, and ignores it, on the other hand leaves the system under the control of the operator, and nothing (should) go wrong (meaning the second level checks should catch the problem)
The general guideline is defensive programming when starting up, with a force switch to override it (so the system can be (re)started if operators decide that's the best outcome). Once the program is running, total programming should be your go-to solution. When in doubt, do the best you can and continue on to the next request.
Since I've been programming million qps+ systems, I've learned that there's even nothing wrong with almost totally ignoring errors. You'd be surprised how well the following works: before handling a request, note down the time (using the cheap instruction), then every time you leave your method, check the time. If it's over a timeout, increase a counter, log if not logged in the past 10s, and send an empty reply. This makes the developer's job harder, but makes everybody else a lot happier.
> I've learned that there's even nothing wrong with almost totally ignoring errors.
I sincerely feel bad for developers who work with people who have attitudes like the above. Detecting production issues is miserable with code like that, let alone debugging them.
I sincerely feel bad for developers who work with people who have attitudes like the above. Detecting production issues is miserable with code like that, let alone debugging them.
A bare "-" argument has a specific meaning in other unix programs, like "read from stdin". Giving it a different meaning like "no meaning so ignored" is inconsistent and misleading. If "-Y" has no meaning but is not ignored because it generates an error message, then if "-" has no meaning it should also generate the identical error message.
> And causing errors for everything will cause your program to bug out in perfectly valid cases.
Erroring out is admittedly not a panacea to every situation, but the user-facing end of a command line interface is pretty low hanging fruit and a pretty obvious place to error out. The nuclear reactor equivalent wouldn't be the low level control loop, it'd be how the display panels react to operator inputs and sensors - the red lights they turn on, the klaxons they sound, the systems they engage to attempt to put the reactor into a safe state when it thinks it's getting ready to melt down.
And even for that low level control loop, you'd better believe they're thinking very very hard about, and once again intentionally define, how they handle any edge cases they can think of, not just throwing caution to the wind and letting the program's behavior fall where it may.
Even for a rocket, sometimes the best answer is "do nothing - and let the range safety systems blow the damn thing up if that wasn't the right answer."
> Since I've been programming million qps+ systems, I've learned that there's even nothing wrong with almost totally ignoring errors. You'd be surprised how well the following works: before handling a request, note down the time (using the cheap instruction), then every time you leave your method, check the time. If it's over a timeout, increase a counter, log if not logged in the past 10s, and send an empty reply. This makes the developer's job harder, but makes everybody else a lot happier.
Totally ignoring errors leaves you with crashy garbage that does not accomplish your goal of high uptime/availability/not corrupting data in C++ - I'd wager you're dealing with safer languages to type that with a straight face! Even there, though, you probably write code to at least handle null references and other edge cases. You might not trigger fatal assertion dialogs, you might not log to some fancy telemetry system, you might not even log at all - but something to handle error conditions.
And if you're writing that code anyways, you might as well write some logs/telemetry as well to make your devs lives easier. You don't have to force it into the face of your end users, you don't have to make the whole thing explode in the face of adversity, but some opt-in dev tools for yourself tends to be nice.
A fun trick from gamedev: "Assertion" macros that force you to include an error handling statement (often a simple "return;"). Devs get to check out if that null pointer passed to your leaderboards is a systemic bug that broke all leaderboards, gamers get to keep their quest progress instead of the entire game crashing because a server being down or giving a malformed response means the game doesn't know how to handle updating a single leaderboard occasionally.
Best of both worlds. Be greedy - you can have happy users and devs.
Erroring out is admittedly not a panacea to every situation, but the user-facing end of a command line interface is pretty low hanging fruit and a pretty obvious place to error out. The nuclear reactor equivalent wouldn't be the low level control loop, it'd be how the display panels react to operator inputs and sensors - the red lights they turn on, the klaxons they sound, the systems they engage to attempt to put the reactor into a safe state when it thinks it's getting ready to melt down.
And even for that low level control loop, you'd better believe they're thinking very very hard about, and once again intentionally define, how they handle any edge cases they can think of, not just throwing caution to the wind and letting the program's behavior fall where it may.
Even for a rocket, sometimes the best answer is "do nothing - and let the range safety systems blow the damn thing up if that wasn't the right answer."
> Since I've been programming million qps+ systems, I've learned that there's even nothing wrong with almost totally ignoring errors. You'd be surprised how well the following works: before handling a request, note down the time (using the cheap instruction), then every time you leave your method, check the time. If it's over a timeout, increase a counter, log if not logged in the past 10s, and send an empty reply. This makes the developer's job harder, but makes everybody else a lot happier.
Totally ignoring errors leaves you with crashy garbage that does not accomplish your goal of high uptime/availability/not corrupting data in C++ - I'd wager you're dealing with safer languages to type that with a straight face! Even there, though, you probably write code to at least handle null references and other edge cases. You might not trigger fatal assertion dialogs, you might not log to some fancy telemetry system, you might not even log at all - but something to handle error conditions.
And if you're writing that code anyways, you might as well write some logs/telemetry as well to make your devs lives easier. You don't have to force it into the face of your end users, you don't have to make the whole thing explode in the face of adversity, but some opt-in dev tools for yourself tends to be nice.
A fun trick from gamedev: "Assertion" macros that force you to include an error handling statement (often a simple "return;"). Devs get to check out if that null pointer passed to your leaderboards is a systemic bug that broke all leaderboards, gamers get to keep their quest progress instead of the entire game crashing because a server being down or giving a malformed response means the game doesn't know how to handle updating a single leaderboard occasionally.
Best of both worlds. Be greedy - you can have happy users and devs.
> Totally ignoring errors leaves you with crashy garbage that does not accomplish your goal of high uptime/availability/not corrupting data in C++ - I'd wager you're dealing with safer languages to type that with a straight face! Even there, though, you probably write code to at least handle null references and other edge cases. You might not trigger fatal assertion dialogs, you might not log to some fancy telemetry system, you might not even log at all - but something to handle error conditions.
That is exactly what I mean. Defensive programming is erroring out and refusing to do anything from that point forward (think of it like an uncaught exception with less information). "Total" programming is doing the best you can, given what's available. Generally if I am unable to do something, or look something up, I'll return a partially filled out request, log it (logs are rate-limited VERY early in the logging process), and increase a counter created for that particular case.
(I do use C++ often, but we use variable guards to guard against null pointers, use-after-free, and sharing (unless explicit)).
> A fun trick from gamedev: "Assertion" macros that force you to include an error handling statement
Link ? I'm interested.
That is exactly what I mean. Defensive programming is erroring out and refusing to do anything from that point forward (think of it like an uncaught exception with less information). "Total" programming is doing the best you can, given what's available. Generally if I am unable to do something, or look something up, I'll return a partially filled out request, log it (logs are rate-limited VERY early in the logging process), and increase a counter created for that particular case.
(I do use C++ often, but we use variable guards to guard against null pointers, use-after-free, and sharing (unless explicit)).
> A fun trick from gamedev: "Assertion" macros that force you to include an error handling statement
Link ? I'm interested.
> Defensive programming is erroring out and refusing to do anything from that point forward (think of it like an uncaught exception with less information)
I’m not sure where you got that impression, but it’s not the generally accepted definition.
Defensive programming does not imply crash/abort/exit, it just simply implies a style of programming where you don’t trust “things will always be ok”. That could involve checking every input for correctness, checking every function output, handling all exceptions, etc. Yes, a defensive method could throw an exception on invalid input, but if the entire program is written defensively, then it should be handled and potentially continued.
I’m not sure where you got that impression, but it’s not the generally accepted definition.
Defensive programming does not imply crash/abort/exit, it just simply implies a style of programming where you don’t trust “things will always be ok”. That could involve checking every input for correctness, checking every function output, handling all exceptions, etc. Yes, a defensive method could throw an exception on invalid input, but if the entire program is written defensively, then it should be handled and potentially continued.
> Link ? I'm interested.
The examples I'm thinking of are all closed source, but here's a trivial implementation on the simpler end of the scale in my favorite style/variation of the idea:
1) Define a name and default severity - such that you can squelch false positives that snuck into the build before you can create and deploy a new one, or enable slower debug checks that might be skipped by default.
2) Configure where the logs go or what categories the messages will be filtered into.
3) Tag JIRA tasks or bug numbers to automatically reopen, or specific authors to alert.
Although these can also be handled in a more orthogonal manner.
The examples I'm thinking of are all closed source, but here's a trivial implementation on the simpler end of the scale in my favorite style/variation of the idea:
#include <iostream>
#include <sstream>
namespace xyz { constexpr bool logFails = true; }
#define XYZ_CHECK_MSG(cond, msg, expr) if (!(cond)) { \
if (::xyz::logFails) { ::std::cerr << msg << ::std::endl; } \
expr; \
} else ((void)0) /* ; */
#define XYZ_CHECK(cond, expr) XYZ_CHECK_MSG(cond, "XYZ_CHECK(" #cond ", ...) failed", expr);
void increment (long * i) {
XYZ_CHECK(i, return); // nonfatal
++*i;
}
int main(int argc, char ** argv) {
XYZ_CHECK_MSG(argc > 1, "Usage: " << argv[0] << " [number] [number]", std::exit(1)); // super fatal
for (int iArg = 1; iArg < argc; ++iArg) {
const char * const arg = argv[argc];
char * argEnd = nullptr;
long n = std::strtol(argv[iArg], &argEnd, 10);
// doesn't even end the function - "continue" could be replaced with "n=0" as well!
XYZ_CHECK_MSG(arg != argEnd && *argEnd == '\0', "Argument " << iArg << " was not a number", continue);
increment(&n);
std::cout << n << "\n";
}
}
XYZ_CHECK_MSG(condition, "Something bad happened, but let's just continue on our way.", );
1) Define a name and default severity - such that you can squelch false positives that snuck into the build before you can create and deploy a new one, or enable slower debug checks that might be skipped by default.
2) Configure where the logs go or what categories the messages will be filtered into.
3) Tag JIRA tasks or bug numbers to automatically reopen, or specific authors to alert.
Although these can also be handled in a more orthogonal manner.
This is something that intrigues me about well-written low-level code. If you make some concessions on expected behaviour, the code can be really clean and simple. But you have to know which concessions are acceptable yet yield this result, and that's super hard, at least to me.
Worse, if someone else has to change the code, even if that someone is author a few months/years later, those concessions will be unknown, breaking the code in strange ways very hard to debug.
Don't forget that the code is now trivial: It's easy to see corner cases since the logic is so small and therefore quite "round". There is not really room for code "breaking in strange ways". It's rather that we can now think more mathematically and more uniformly about the program's behaviour.
It doesn't matter anymore if a given curiosity (like "-" options) is categorized as a concession or just as the way it's supposed to be. In any way it's the way that makes more sense from a mathematical standpoint. If there really was some client code depending on a curiosity, it's also easy to spot and change. But usually that's not even needed.
It doesn't matter anymore if a given curiosity (like "-" options) is categorized as a concession or just as the way it's supposed to be. In any way it's the way that makes more sense from a mathematical standpoint. If there really was some client code depending on a curiosity, it's also easy to spot and change. But usually that's not even needed.
It wouldn't be difficult to disallow these cases, but is that a problem after all? My opinion is that the requirements should be shaped (also) by what logic is required on the implementation side.
And in any case, there's no justification to change the style and make an incomprehensible thicket of vague "abstractions". There's at most one to write slightly more logic.
And in any case, there's no justification to change the style and make an incomprehensible thicket of vague "abstractions". There's at most one to write slightly more logic.
If you want to, you can handle that in the switch statement:
case 'x':
if(x_set) {
fprintf(stderr, “can’t set x twice”);
err = 1;
} else {
x_set = true;
}
break;
Wouldn't an empty flag be caught by the default handler? And duplicate flag usage isn't inherently incorrect (-vvv); handling that would be in the switch statement, and if its actually a boolean switch, then duplicates would just be ignored anyways, so harmless.
The empty flag(s) would be processed by *s != '\0' and result in noops. The point in the early days wasn't to handle corner cases like these gracefully. That only came later as the audience for shell commands widened.
If you learn getopt, you will know having -x multiple times is not an error. It is a feature. For example, you can specify multiple files of the same type with one option. I agree silently ignoring those empty "-" is not desired.
Extract this into its own function and you basically have getopt() --- the POSIX version, not the rather more bloaty GNU version that has sometimes-unexpected behaviour (like reordering arguments).
If you like this sort of source code, I'd also recommend looking at the BSD standard utilities --- they have a similar simple and concise style.
Yet there's still one small simplification that can be made: the condition in the inner loop doesn't need "!= '\0'".
If there are many pure-binary options, then putting them in a bitflag is also an easy extension to the present code:
Indeed, compare with the "modern" way of doing it:
https://github.com/commandlineparser/commandline/tree/master...
...or something slightly simpler (because it's only one file!):
https://github.com/mono/mono/blob/master/mcs/class/Mono.Opti...
It may seem like an exaggeration, but in my experience working with C# and Java, code like that is the norm --- the core functionality is obscured by being scattered amongst a large amount of "fluff" and it's hard to get the whole picture of how it works because the flow jumps around so much. In contrast, the C code in this article can be understood by just staring at it for a little bit --- the entire functionality is contained within less than a dozen lines.
If you like this sort of source code, I'd also recommend looking at the BSD standard utilities --- they have a similar simple and concise style.
Yet there's still one small simplification that can be made: the condition in the inner loop doesn't need "!= '\0'".
If there are many pure-binary options, then putting them in a bitflag is also an easy extension to the present code:
char binopts[] = "abcdefg";
char *opt;
if(opt = strchr(binopts, *s))
options |= 1 << (optidx - opt);
else
// put the switch(*s) here
Indeed, compare with the "modern" way of doing it:
https://github.com/commandlineparser/commandline/tree/master...
...or something slightly simpler (because it's only one file!):
https://github.com/mono/mono/blob/master/mcs/class/Mono.Opti...
It may seem like an exaggeration, but in my experience working with C# and Java, code like that is the norm --- the core functionality is obscured by being scattered amongst a large amount of "fluff" and it's hard to get the whole picture of how it works because the flow jumps around so much. In contrast, the C code in this article can be understood by just staring at it for a little bit --- the entire functionality is contained within less than a dozen lines.
> compare with the "modern" way of doing it
The examples you’ve linked implement much larger set of functionality.
They de-serialize arguments into strongly typed values (validating arguments), validate against unknown commands/options, print various help messages, support globalization, support arrays in a single argument, and lots more.
Sure it’s overkill for a simple app with just a couple of options, but once you have sufficiently complex command line interface, this modern way becomes much simpler than what’s possible with C.
Compare with “old school” way of doing it: https://github.com/gcc-mirror/gcc/blob/master/gcc/opts.c https://github.com/gcc-mirror/gcc/blob/master/gcc/opts-globa... https://github.com/gcc-mirror/gcc/blob/master/gcc/opts-commo...
BTW that thing isn’t even localized, i.e. everything’s US English-only.
The examples you’ve linked implement much larger set of functionality.
They de-serialize arguments into strongly typed values (validating arguments), validate against unknown commands/options, print various help messages, support globalization, support arrays in a single argument, and lots more.
Sure it’s overkill for a simple app with just a couple of options, but once you have sufficiently complex command line interface, this modern way becomes much simpler than what’s possible with C.
Compare with “old school” way of doing it: https://github.com/gcc-mirror/gcc/blob/master/gcc/opts.c https://github.com/gcc-mirror/gcc/blob/master/gcc/opts-globa... https://github.com/gcc-mirror/gcc/blob/master/gcc/opts-commo...
BTW that thing isn’t even localized, i.e. everything’s US English-only.
What in the world is this inconsistent and bizarre spacing around brackets? I literally thought it was a new syntactical construct in C when my eyes first landed on it!
cl_options [next_opt_idx].neg_index == opt_idx
old_decoded_options[i].errors & ~CL_ERR_WRONG_LANG
set_option (opts, (generated_p ? NULL : opts_set),
opt_index, value, arg, kind, loc, dc);GCC works quite well in practice and I don’t care much about a couple of extra/missing spaces in its source code. The answer to your question is probably “because the software has been developed for decades by thousands of unrelated people”.
Personally, I don’t write code like this, because I spam “autoformat” hotkey in the IDE :-)
Personally, I don’t write code like this, because I spam “autoformat” hotkey in the IDE :-)
Once upon a time, programmers didn't have IDE's, Emacs, or even text editors. I'd been programming for seven or eight years before Bill Joy created vi. Each programmer and each program had its own style.
Often, a program's layout reflected the programmer's inner thoughts as he or she worked through the creation of the code. Expressions were written like a mathematician might write, with spacing and bracketing reflecting some way of thinking about the grouping of the abstractions at hand.
This is just a random routine, written around 1975, from Niklaus Wirth's PL/0 compiler for Pascal, the programming language that he created. The indenting is wild by contemporary standards:
[1] http://pascal.hansotten.com/niklaus-wirth/pl0/
[2] John Lions, Lion's Commentary on Unix 6th Edition with Source Code. https://www.amazon.com/Lions-Commentary-Unix-John/dp/1573980...
Often, a program's layout reflected the programmer's inner thoughts as he or she worked through the creation of the code. Expressions were written like a mathematician might write, with spacing and bracketing reflecting some way of thinking about the grouping of the abstractions at hand.
This is just a random routine, written around 1975, from Niklaus Wirth's PL/0 compiler for Pascal, the programming language that he created. The indenting is wild by contemporary standards:
procedure getch;
begin if cc = ll then
begin if eof(input) then
begin write(' program incomplete'); goto 99
end;
ll := 0; cc := 0; write(cx: 5,' ');
while not eoln(input) do
begin ll := ll+1; read(ch); write(ch); line[ll]:=ch
end;
writeln; readln; ll := ll + 1; line[ll] := ' ';
end;
cc := cc+1; ch := line[cc]
end {getch};
setfs(dev)
{
register struct mount *p;
register char *n1, *n2;
for(p = &mount[0]; p < &mount[NMOUNT]; p++)
if(p->m_bufp != NULL && p->m_dev == dev) {
p = p->m_bufp->b_addr;
n1 = p->s_nfree;
n2 = p->s_ninode;
if(n1 > 100 || n2 > 100) {
prdev("bad count, dev);
p->s_nfree = 0;
p->s_ninode = 0;
}
return(p);
}
panic("no fs");
}
[1] http://pascal.hansotten.com/niklaus-wirth/pl0/
[2] John Lions, Lion's Commentary on Unix 6th Edition with Source Code. https://www.amazon.com/Lions-Commentary-Unix-John/dp/1573980...
>Often, a program's layout reflected the programmer's inner thoughts
And often it reflects the programmer's inner carelessness and disrespect for other programmers who have to deal with their code.
And often it reflects the programmer's inner carelessness and disrespect for other programmers who have to deal with their code.
>Yet there's still one small simplification that can be made: the condition in the inner loop doesn't need "!= '\0'".
I believe this would cause the newline not to be printed in the unknown command error, so it is necessary.
I believe this would cause the newline not to be printed in the unknown command error, so it is necessary.
How? '\0' is the same value as 0 (only with a different type, which doesn't matter in this case), and if(x != 0) is the same as if(x).
> a different type
This is true in C++ but not in C.
This is true in C++ but not in C.
Skimmed through the article and found a small mistake.
That means that (*argv)[0] is the first character of the program name and (*argv)[1] is the first character of the first argument.
"That’s how Kernigham and Ritchie did it in 1978. Nowadays they just haul in the software weenies with their fancy objects and methods."
No, we use getopts(3C). For decades now. I even use getopts in my shell programs. For old UNIX hands, using getopts in C or in shell programming is certainly nothing new. How, you ask? Simple! Watch this:
while getopts hDd: Option
do
case "$Option"
in
h)
Usage
;;
D)
Debug=true
;;
d)
Destination="$OPTARG"
;;
esac
done
shift `expr $OPTIND - 1` # I did not use $((OPTIND - 1)) for a reason!On the topic of processing command-line arguments and the recent post on obscure things you can do with C: My "magic getopt" (http://www.daemonology.net/blog/2015-12-06-magic-getopt.html) does some very evil things to make it possible to write a "normal-looking" C getopt look which accepts both short and long options.
this is how they did it somewhat later in plan 9, with macro's:
ARGBEGIN{ default: usage(); case 'm': m = ARGF(); break; case 'p': pflag = 1; break; }ARGEND
https://github.com/9fans/plan9port/blob/master/include/libc.... https://github.com/9fans/plan9port/blob/master/src/cmd/mkdir...
ARGBEGIN{ default: usage(); case 'm': m = ARGF(); break; case 'p': pflag = 1; break; }ARGEND
https://github.com/9fans/plan9port/blob/master/include/libc.... https://github.com/9fans/plan9port/blob/master/src/cmd/mkdir...
The Plan 9 solution always felt really logical imo.
i agree. too "clever", feels like a needless optimization. (optimizing for fewer keystrokes to type? or obscurity?)
btw, many of the plan 9 commands use slightly different/custom option parsing. probably for historic reasons.
btw, many of the plan 9 commands use slightly different/custom option parsing. probably for historic reasons.
No, this isn't clever at all. Its an optimization for when you need to write a lot of little utilities that need to parse arguments. It probably came out of a day of writing tools, and after the fifth time of rewriting that while/for loop someone got pissed and made that macro. I use this macro all the time on both 9front and unix because it makes parsing arguments trivial (and I don't use long options, but that's more because I'm a plan 9/unix extremist than for any technical reasons).
"What's so cool about this is its flexibility."
This is something I have never understood.
I am a connoisseur of command line progams. I have used hundreds of them over decades. I write command line programs and scripts every week. It is an obsession. Yet I am embarassed to admit that honestly I have never understood the benefits of flexibility with passing arguments. I never understood the "getopt" movement. I do not use it. All my programs are very simple and straightforward without heaps fo options.
I apologise for being obtuse, but what am I missing?
To anyone who might be offended: I am not criticising flexibility of commandline arguments or its coolness. I just want to understand what are the practical advantages over something more simple and less flexible, like what I prefer. Only if I understand the advantages can I be an advocate for using numerous commandline options and flexibile parsing.
(Theres another post about setenv et al. on the front page right now. For programs that read from environ variables -- which can be a better alternative to using heaps of commandline options IMO -- I just use envdir from daemontools.)
This is something I have never understood.
I am a connoisseur of command line progams. I have used hundreds of them over decades. I write command line programs and scripts every week. It is an obsession. Yet I am embarassed to admit that honestly I have never understood the benefits of flexibility with passing arguments. I never understood the "getopt" movement. I do not use it. All my programs are very simple and straightforward without heaps fo options.
I apologise for being obtuse, but what am I missing?
To anyone who might be offended: I am not criticising flexibility of commandline arguments or its coolness. I just want to understand what are the practical advantages over something more simple and less flexible, like what I prefer. Only if I understand the advantages can I be an advocate for using numerous commandline options and flexibile parsing.
(Theres another post about setenv et al. on the front page right now. For programs that read from environ variables -- which can be a better alternative to using heaps of commandline options IMO -- I just use envdir from daemontools.)
>Yet I am embarassed to admit that honestly I have never understood the benefits of flexibility with passing arguments.
It's about not having to remember what goes before what, if you can put them like this or that, etc ON TOP of remembering the arguments themselves.
>All my programs are very simple and straightforward without heaps fo options.
If your programs are basically ./a.out then perhaps you're not the target audience for getopts?
It's about not having to remember what goes before what, if you can put them like this or that, etc ON TOP of remembering the arguments themselves.
>All my programs are very simple and straightforward without heaps fo options.
If your programs are basically ./a.out then perhaps you're not the target audience for getopts?
To add to your point, it's really simple, clear, and flexible to just use environment variables as program arguments, as in
$ FOO=BAR THIS=THAT ./myprog
Part of the Unix philosophy is that every program should be a filter, one that can take input from stdin and output to stdout, so that it can be used in conjunction with other programs (which may not have been written yet). If you wanted to add an optional feature to your program/script and didn't know what parts of it could be changed without breaking places where it was used, adding it as a non-default option allows you to do this seamlessly.
[deleted]
One thing an old school C programmer would not do is neglect to put parens around their blocks.
Ritchie is the person who made the decision to make curlies optional in C. That's strong evidence he wouldn't add extraneous curlies to his code.
On the contrary! We force all our blocks to consist of a single statement so that we can always omit the damn parens.
Are you saying you need statements in your loop blocks!? I just added this to a school assignment:
for (String next = in.readLine();
next != null && dictionary.add(next);
next = in.readLine());
I wasn't all that impressed with the code - too 'clever' and concise for me.
I wouldn't be surprised if it let a bunch of unexpected inputs through as another commentor pointed out.
That may have been okay back then but in today's hostile environment and with so many people around that aren't natural programmers who dream of pointers you probably want something a bit more verbose.
I've been programming C since the late 80s so I'm not a new-comer. But I'm not a fan of that code even though I can understand it okay.
The more experience I get and the more people I work with, the simpler I like my code to be. I'll always take simplicity over speed and concision if I can.
I wouldn't be surprised if it let a bunch of unexpected inputs through as another commentor pointed out.
That may have been okay back then but in today's hostile environment and with so many people around that aren't natural programmers who dream of pointers you probably want something a bit more verbose.
I've been programming C since the late 80s so I'm not a new-comer. But I'm not a fan of that code even though I can understand it okay.
The more experience I get and the more people I work with, the simpler I like my code to be. I'll always take simplicity over speed and concision if I can.
The getopt() arguments we used to have on USENET before gnu swept the board..
Maybe I've forgotten more C than I'd like to admit,
edit: clarity
while (--argc > 0 && (*++argv)[0] == '-')
...
Notice that the decrement always occurs before the ‘>’ is
evaluated. This would be true even if it were postfix (i.e., argc-- > 0).
edit: clarity
The decrement is the same either way, the value yielded by the decrement expression would however be different. I don't like the wording either.
What's clever about this? It's a little obtuse and overly permissive. How do most developers parse arguments? I suspect it would be a for loop with nested if statements - since you can't switch on strings. If you expect a value to follow the flag you increment the counter in your if block and 'continue'.
It’s nice and smart, but also notice how it needs a whole web page to explain and would happily compile after a lot of invisible single-letter changes that would introduce horrible bugs. There is value in the old ways of writing software, I just wouldn’t throw out modern software engineering just yet.
Any competent C programmer shouldn't need any explanation of that simple example.
Granted pointers, just like objects in more "modern" languages, take some while for new programmers a while to get their heads around.
Granted pointers, just like objects in more "modern" languages, take some while for new programmers a while to get their heads around.
>Any competent C programmer shouldn't need any explanation of that simple example.
Interesting point, and I agree. I read that code a little earlier today, and (was a bit surprised to see that) I could understand it pretty much right away, even though I have not used C a lot for a while. I did use it a lot earlier though, on both Unix and DOS/Windows, and I do remember poring over that K&R book early in my C career, and working out the meaning of each line of code in almost the whole book. That may be why I could figure out quickly what it meant, now. More cryptic stuff might take a while to figure out, though, but the point I want to make is that the general principle remains the same: you have to understand what each line and even what each token (of the code) in each line is doing, how it works, etc., by reading the books and docs, by trial and error, modifying the code and seeing the modified output, using debugging print statements, isolating smaller chunks of code and running them to see how they work and if your mental model of what is happening matches reality, etc.
Interesting point, and I agree. I read that code a little earlier today, and (was a bit surprised to see that) I could understand it pretty much right away, even though I have not used C a lot for a while. I did use it a lot earlier though, on both Unix and DOS/Windows, and I do remember poring over that K&R book early in my C career, and working out the meaning of each line of code in almost the whole book. That may be why I could figure out quickly what it meant, now. More cryptic stuff might take a while to figure out, though, but the point I want to make is that the general principle remains the same: you have to understand what each line and even what each token (of the code) in each line is doing, how it works, etc., by reading the books and docs, by trial and error, modifying the code and seeing the modified output, using debugging print statements, isolating smaller chunks of code and running them to see how they work and if your mental model of what is happening matches reality, etc.
Having learned pointers in other languages before learning C, I never understood what is so hard about them.
Even BASIC had them via peek and poke.
Don't people learn to draw boxes and arrows anymore?
Even BASIC had them via peek and poke.
Don't people learn to draw boxes and arrows anymore?
[deleted]
Wow, the amount of compactness and craftsmanship in these lines of code is amazing.
I think there's nothing magical about it at all. It's rather that "modern software architecture" (examples for what I mean linked in another comment here about C# and Java) is a disaster.
It might not even be that. I presume that kind of code used to be written with pen and paper, a compilation cycle almost prohibitively expensive.
When you sit down and just design a piece of code for hours as to not waste your compilation cycle, I would guess that you naturally end up being fairly crafty after some time.
When you sit down and just design a piece of code for hours as to not waste your compilation cycle, I would guess that you naturally end up being fairly crafty after some time.
Nope, you just end up thinking that compactly as you type.
When I learned C it was a given to code efficiently. Pointer manipulation and efficient structure packing was expected, and therefore taught. You'd rule out of an interview anyone who didn't easily grok it.
It's probably no surprise that the fastest GUI editor I've used to date ran on a 7.1MHz machine. Such is "progress"!
When I learned C it was a given to code efficiently. Pointer manipulation and efficient structure packing was expected, and therefore taught. You'd rule out of an interview anyone who didn't easily grok it.
It's probably no surprise that the fastest GUI editor I've used to date ran on a 7.1MHz machine. Such is "progress"!
Just because I'm curious, CygnusEd?
Yes indeed. :)
Most impressive, I think, is that it managed to be so fast and include smooth scrolling.
Most impressive, I think, is that it managed to be so fast and include smooth scrolling.
Brief was pretty fast too. I only used it briefly (heh), but read in some computer magazines at the time, that it used a lot of code optimizations, one of which was that it used assembly language code, and another being (IIRC) that it used BIOS calls to dynamically change the speed of movement of the cursor when it detected that you pressed an arrow key for a longer time (probably by changing the key repeat rate or reducing the repeat time), so that when you did that, movement through the file would be faster. The idea being that a user pressing the arrow key for a longer time probably meant to move through a longer section of the file (than usual) to reach some other distant place in it, so Brief figures this out and assists them with that, by scrolling faster with that BIOS technique.
Anecdote: On a trip to the US (Boston), I once met Norm Miles, who, my US colleague said, was the creator of Brief.
The Brief editor is actually still available, here, and for free now:
http://www.briefeditor.com/
https://en.wikipedia.org/wiki/Brief_(text_editor)
Anecdote: On a trip to the US (Boston), I once met Norm Miles, who, my US colleague said, was the creator of Brief.
The Brief editor is actually still available, here, and for free now:
http://www.briefeditor.com/
https://en.wikipedia.org/wiki/Brief_(text_editor)
Amazing from today's perspective, but not surprising. With just a few KB of memory, minimalistic rather than modern expressive style was just natural.
I get cynic when "modern style" approaches with their megabytes and gigabytes of junk code that does nothing (or nothing anyone could clearly define) is called "expressive".
Many of the modern conveniences might be expressive in the small (function level). But it quickly gets highly unexpressive as you move to a more global level. That is because this "expressiveness" is often achieved by arbitrary and non-orthogonal approaches, which increases dependencies and hinders modularity. In the end, it's only more convenient to paint yourself into a corner. Seen that in many codebases.
Many of the modern conveniences might be expressive in the small (function level). But it quickly gets highly unexpressive as you move to a more global level. That is because this "expressiveness" is often achieved by arbitrary and non-orthogonal approaches, which increases dependencies and hinders modularity. In the end, it's only more convenient to paint yourself into a corner. Seen that in many codebases.
The original getopt was a really tight library.
I do think this is even more concise than they would have written in maintained code. In particular, I believe the missing {}'s for the 'while' and 'for' loops whouldn't have been left away, but I might be mistaken. Compare, for example, with this gem:
https://www.cs.princeton.edu/courses/archive/spr09/cos333/be... (submitted as https://news.ycombinator.com/item?id=5672875 some time ago)
There Kernighan talks about a piece of code written by Rob Pike for inclusion in a different book; the code was written to be as small as possible while still including some useful functionality. In particular, Pike made well-considered choices about which functionality to include and which to exclude, but there are also some of those expressions that will not be completely transparent to the beginner C programmer. But the goal was writing short code, and clarity came secondary, but also emerged partly as a result of the first.