CODEWITHSUNDEEP
cgcc-warning
user214181
user214181

Reputation:

C: warns about implicit long to int conversion

I was wondering whether there is a way to tell the compiler (I'm on gcc version 4.1.2 20080704 (Red Hat 4.1.2-46) or icc 11.1) to throw a warning whenever a long-to-int implicit conversion takes place. For example, compiling the file test.c which contains the code:

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char** argv)
{
    int n = atol(argv[1]);
    printf("int: %d\n", n);
    long int N = atol(argv[1]);
    printf("long: %ld\n", N);

    return 0;
}

with:

gcc -Wall -Wconversion test.c -o test

does not produce any warnings. Running the resulting binary as

./test 12345678901

I get, as expected:

int: -539222987
long: 12345678901

as the number 12345678901 has overflown the int but not the long. I'd like the compiler to tell me whenever something like this might happen. The option -Wconversion unexpectedly (to me) does not do that.

Upvotes: 4

Views: 3289

Answers (3)

Stephen Canon
Stephen Canon

Reputation: 106317

Check if your gcc version has -Wshorten-64-to-32. Be prepared for a deluge of possibly spurious double -> float conversion warnings if you use floating-point in your code.

edit: I think shorten-64-to-32 may be an Apple extension that mainline never picked up, sadly. So you may be out of luck unless you upgrade to gcc-4.3 or higher.

Upvotes: 4

Mark Byers
Mark Byers

Reputation: 839074

Try gcc 4.3.0

http://gcc.gnu.org/wiki/NewWconversion

Upvotes: 3

Christoph
Christoph

Reputation: 169763

The behaviour of -Wconversion changed with GCC4.3 - update your compiler and try again (can't check if it really works myself as I'm on a 32bit system, but as the warning gets correctly emitted for atoll, it should)...

Upvotes: 0

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