How to stop GCC complaining about “directive output may be truncated” in snprintf() call?

Question

I\'m using GCC 9.2.0 on both an ancient Linux (RedHat 5.2) and modern macOS 10.14.6 Mojave, and I get the same complaint on both.

#include 
#i         


        

Answer 1

With compilers that check the range of possible values, use % to quickly limit the range.

% some_unsigned_N insures the output is in [0... N-1].

Note that % some_pos_int_N output is in the (-N ...N) range so recommend unsigned math to avoid the '-' sign.

snprintf(ex->mm_yyyy, sizeof(ex->mm_yyyy), "%d-%d", 
    //  tm->tm_mon + 1, tm->tm_year + 1900);
    (tm->tm_mon + 1)%100u, (tm->tm_year + 1900)/10000u);

May also want to use "%u" should some_unsigned_N near INT_MAX.