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?
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2 Answers
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.
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printf (Wikipedia) seems to say that it's for decimal as I had guessed:
d,i
int as a signed decimal number. '%d' and '%i' are synonymous for output, but are different when used with scanf() for input (using %i will interpret a number as hexadecimal if it's preceded by 0x, and octal if it's preceded by 0.)
