Question

Following is some obviously-defective code for which I think the compiler should emit a diagnostic. But neither gcc nor g++ does, even with all the warnings options I could think of: -pedantic -Wall -Wextra

#include <stdio.h>  short f(short x) {     return x; }  int main() {     long x = 0x10000007;   /* bigger than short */     printf('%d\n', f(x));  /* hoping for a warning here */     return 0; } 

Is there a way to make gcc and g++ warn about this? On a side note, do you have another compiler which warns about this by default or in a fairly common extra-warnings configuration?

Note: I’m using GCC (both C and C++ compilers) version 4.2.4.

Edit: I just found that gcc -Wconversion does the trick, but the same option to g++ doesn’t, and I’m really using C++ here, so I need a solution for g++ (and am now wondering why -Wconversion doesn’t seem to be it).

Edit: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34389 suggests that this may be fixed in g++ 4.4…maybe? It’s not clear to me yet if it’s the same issue and/or if the fix is really coming in that version. Maybe someone with 4.3 or 4.4 can try my test case.

Answer 1

Use -Wconversion — the problem is an implicit cast (conversion) from long x to short when the function f(short x) is called [not printf], and -Wconversion will say something like ‘cast from long to short may alter value’.

..

Edit: just saw your note. -Wconversion results in a warning for me, using g++ 4.3.2 on Linux… (4.3.2-1 on Debian)