I know this doesn't sound productive, but I'm looking for a way to remember all of the formatting codes for printf
calls. %s
, %p
, %f
are all obvious, but I can't understand where %d
comes from. Is %i
already taken by something else?
It stands for "decimal" (base 10), not "integer." You can use %x
to print in hexadecimal (base 16), and %o
to print in octal (base 8). An integer could be in any of these bases.
In printf()
, you can use %i
as a synonym for %d
, if you prefer to indicate "integer" instead of "decimal," but %d
is generally preferred as it's more specific.
On input, using scanf()
, you can use use both %i
and %d
as well. %i
means parse it as an integer in any base (octal, hexadecimal, or decimal, as indicated by a 0
or 0x
prefix), while %d
means parse it as a decimal integer.
Here's an example of all of them in action:
#include <stdio.h>
int main() {
int out = 10;
int in[4];
printf("%d %i %x %o\n", out, out, out, out);
sscanf("010 010 010 010", "%d %i %x %o", &in[0], &in[1], &in[2], &in[3]);
printf("%d %d %d %d\n", in[0], in[1], in[2], in[3]);
sscanf("0x10 10 010", "%i %i %i", &in[0], &in[1], &in[2]);
printf("%d %d %d\n", in[0], in[1], in[2]);
return 0;
}
So, you should only use %i
if you want the input base to depend on the prefix; if the input base should be fixed, you should use %d
, %x
, or %o
. In particular, the fact that a leading 0
puts you in octal mode can catch you up.