Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Highlighted
Beginner
5 Views

ICC: Multiple issues when header not included

With ICC 19.0.1.144 as well as older versions I experience the following behavior which I think are bugs in the compiler:

Take the following very simple code:

#include <stdio.h>

int main (int argc, char* argv[]) {
	printf("%f\n", fabs(0.5));
	return 0;
}

It's missing an include of math.h for fabs(). However, when compiling it with ICC using -Wmissing-prototypes I receive no warning. Instead it silently generates a prototype for fabs() and works as intended:

$ icc -Wmissing-prototypes -o test test.c
$ ./test
0.500000

Using -Wall also does not show it. Is that how it's supposed to be?

Now, here comes the second issue: If I compile the code with -g to include debugging symbols, ICC suddenly thinks of a wrong signature for fabs(), returning an int. Again, I receive no warning about the missing prototype:

$ icc -g -Wmissing-prototypes -o test test.c
$ ./test
0.000000

Note that the behavior of the program changed by adding -g to the compiler call. This does not seem right to me... One gets a bit more insight into this calling icc with -Wall, since printf() isn't happy here:

$ icc -g -Wall -o test test.c
test.c(4): warning #181: argument of type "int" is incompatible with format "%f", expecting argument of type "double"
  	printf("%f\n", fabs(0.5));
  	               ^

(Post edited on 01/12/2019 to fix formatting and missing includes)

0 Kudos
5 Replies
Highlighted
Moderator
5 Views

Are there anything that I've missed as I couldn't compile your test case.

vahoang@orcsle147:/tmp$ icc t.c -V

Intel(R) C Intel(R) 64 Compiler for applications running on Intel(R) 64, Version 19.0.1.144 Build 20181018

t.c(1): catastrophic error: expected a file name
  #include
          ^

compilation aborted for t.c (code 4)
vahoang@orcsle147:/tmp$
vahoang@orcsle147:/tmp$ cat t.c
#include

int main (int argc, char* argv[]) {
printf("%f\n", fabs(0.5));
return 0;
}
vahoang@orcsle147:/tmp$

0 Kudos
Highlighted
Beginner
5 Views

Yes, the forum software has removed all parts of my post containing angle brackets... For some reason I didn't have a proper editor when creating this post. Here's the code again:

#include <stdio.h>

int main (int argc, char* argv[]) {
	printf("%f\n", fabs(0.5));
	return 0;
}

And it's missing an include of math.h.

0 Kudos
Highlighted
Moderator
5 Views

For the first issue, you can add -w to see the warning.

vahoang@orcsle147:/tmp$ icc t.c  -w3
t.c(5): remark #266: function "fabs" declared implicitly
  printf("%f\n", fabs(0.5));
                 ^
I'll get back to you on the second one.

Thanks,

0 Kudos
Highlighted
Moderator
5 Views

Another way to get the warning is to compile with -Wimplicit-function-declaration

I've reported the second issue to our developer. The tracking number is CMPLRIL0-31028

 

0 Kudos
Highlighted
Beginner
5 Views

Oh, indeed I confused -Wmissing-prototypes with -Wimplicit-function-declaration. But shouldn't -Wall include -Wimplicit-function-declaration?

Thanks for filing the problem report regarding the second issue!

0 Kudos