c语言prog.c: in function 'main':,c - Warning: ignoring return value of 'scanf', declared with attribut...

After reading all answers and comments on this page I don't see these yet another options to avoid the warning:

When compiling with gcc you can add to your command line:

gcc -Wall -Wextra -Wno-unused-result proc.c -o prog.x

Another option is to use -O0 as "optimization level zero" ignores the warning.

Using cast to (void) is simply useless when compiling with gcc

If debugging your code, you can always use assert() as in the example bellow:

u = scanf("%d", &t);

assert(u == 1);

But now, if you turn off assert via #define NDEBUG you will get a -Wunused-but-set-variable. You can then turn off this second warning by one of two ways:

Adding -Wno-unused-but-set-variable to your gcc command line, or

Declaring the variable with attribute: int u __attribute__((unused));

As pointed out in other answer, the second option unfortunately is not very portable, although it seems the best option.

At last, the defined MACRO bellow can help you if you are sure you want to ignore the return of a given function, but you are not comfortable turning off the warnings for all unused returns of functions:

#define igr(x) {__typeof__(x) __attribute__((unused)) d=(x);}

double __attribute__ ((warn_unused_result)) fa(void) {return 2.2;}

igr(fa());