When converting an int like so:
char a[256];
sprintf(a, \"%d\", 132);
what\'s the best way to determine how large a should be? I a
Some here are arguing that this approach is overkill, and for converting ints to strings I might be more inclined to agree. But when a reasonable bound for string size cannot be found, I have seen this approach used and have used it myself.
int size = snprintf(NULL, 0, "%d", 132);
char * a = malloc(size + 1);
sprintf(a, "%d", 132);
I'll break down what's going on here.
snprintf
tell it that I want to write 0 characters of the result to NULL
. When we do this, snprintf
won't actually write any characters anywhere, it will simply return the number of characters that would have been written. This is what we wanted.char
pointer. Make sure and add 1 to the required size (for the trailing \0
terminating character).char
pointer, we can safely use sprintf
to write the integer to the char
pointer.Of course you can make it more concise if you want.
char * a = malloc(snprintf(NULL, 0, "%d", 132) + 1);
sprintf(a, "%d", 132);
Unless this is a "quick and dirty" program, you always want to make sure to free the memory you called with malloc
. This is where the dynamic approach gets complicated with C. However, IMHO, if you don't want to be allocating huge char
pointers when most of the time you will only be using a very small portion of them, then I don't think this is bad approach.