Question

Possible Duplicate:
Can I make GCC warn on passing too-wide types to functions?

Is there a way to make gcc or g++ produce a warning when I pass a signed int to a function that takes an unsigned int?

For instance:

int main(){
        char buf[8];
        int i;
        for(i=0;i<6;i++)
                buf[i] = 'a';
        buf[6]='\0';
        strcat(buf, " ");
        strncat(buf, "happystacksmashingstring",-1 );
        return 0;

}

will cause stack smashing because strncat takes a size_t as its third argument, which is often an unsigned int. Yet, the command:

g++ -Wall -Wextra -Werror -pedantic -W -Weffc++ -Wconversion test.c

which contains every warning flag I know, produces no errors or warnings at compile time, and a smashed stack at runtime.

gcc -Wall -Wextra -Werror -pedantic -W -Wconversion test.c

will produce errors about the implicit conversions in contrast. Why doesn’t the -Wconversion flag work properly with g++?

Answer 1

From the man page of g++:

Warnings about conversions between signed and unsigned integers are disabled by default in C++ unless-Wsign-conversion is explicitly enabled.