What does a line after function declaration but outside function itself

Question

What does it mean if something like the two lines after the main function declaration appears in C code?

int main(argc,argv)
  int argc;
  char *argv[];
{
  // main function body
}

I've never seen anything like this before. The code works just fine, but I'm curious to know what this means. Thanks!

that's obsolete [K&R syntax](http://stackoverflow.com/questions/3092006/function-declaration-kr-vs-ansi) — Diego, Jun 07 '15 at 01:11

score 1 · Answer 1 · answered Jun 07 '15 at 01:14

1

It is just one other way of declaring the datatype of arguments of that particular function.

answered Jun 07 '15 at 01:14

Gajendra Bagali

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No, it's actually not "just one other way of declaring the datatype of arguments". It's a way of defining the arguments the function receives - but only after those arguments have undergone default argument promotion. – Andrew Henle Jun 07 '15 at 01:15
Yes. You are right! So can I say - the default argument promotion is used when we are not sure of the datatype of receiving arguments. – Gajendra Bagali Jun 07 '15 at 01:26
While it is another way of declaring function arguments, it's a way that's not compatible at all with newer/ANSI/ISO C declarations and definitions. I just wanted to point that out clearly so no one would think they could do something like mix new-style function declarations/prototypes with old K&R style function definitions. – Andrew Henle Jun 07 '15 at 01:32

score 1 · Accepted Answer · edited May 23 '17 at 11:52

1

This is the original (read: ancient) style of declaring argument parameters in K&R C. In ANSI C standards, the form you're likely familiar with has been the standard.

See also: What are the major differences between ANSI C and K&R C?

edited May 23 '17 at 11:52

Community

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answered Jun 07 '15 at 01:14

jangler

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score 1 · Answer 3 · answered Jun 07 '15 at 01:20

That's "K&R" C. It's way out of date.

Don't use it, even if your compiler supports it. Arguments passed to a function defined in that manner will have undergone argument promotion so that every argument has the same size (via the same mechanism that varargs are promoted in up-to-date C code).

Such code also does not support function declarations/prototypes. And never try to "improve" such code by creating function prototypes - you'll break the argument promotion that the function is expecting.

What does a line after function declaration but outside function itself

3 Answers3