The sprintf family of functions ( sprintf , snprintf , vsnprintf , …) have this little-known feature to what size your buffer should be. In cases where you don’t have a fixed upper bound, this is really useful.
For example:
int size = snprintf ( /*str=*/ NULL , /*size=*/ 0 , "%d: %s" , some_int , some_c_str ); if ( size < 0 ) abort (); int size_with_nul = size + 1 ; char * buf = malloc ( size_with_nul ); if ( buf == NULL ) abort (); int result = snprintf ( /*str=*/ buf , /*size=*/ size_with_nul , "%d: %s" , some_int , some_c_str ); if ( result < 0 ) abort ();
I have size_with_nul because snprintf man pages say
The functions snprintf() and vsnprintf() write at most size bytes (including the terminating null byte (‘\0’)) to str .
If you like, check out this tiny header-only library I wrote a couple of years ago and promptly forgot about.
Go forth and please stop manually computing buffer sizes.