printf
"printf" is a function in the C-standard library that outputs text to standard output. Standard output is typically the terminal or debug console, depending on the system the program is running on. The f stands for formatted, allowing the function to output not just fixed strings, but also text with variable data in it.
Contents
Hello world
The simplest of all C-programs is known as "Hello world" program. It outputs "Hello world", using printf.
#include <stdio.h>
int main(void) {
printf("Hello world!\n");
return 0;
}
Using parameters
Parameters need to be specified in the format string. A parameter definition starts with a % character. A simple example with one numerical parameter looks as below:
printf("Total sum is: %d\n", Sum);
Parameter specification
Type specification
Type field
The Type field can be any of:
Character Description %
Prints a literal %
character (this type doesn't accept any flags, width, precision, length fields).d
,i
int
as a signed decimal number.%d
and%i
are synonymous for output, but are different when used withscanf()
for input (where using%i
will interpret a number as hexadecimal if it's preceded by0x
, and octal if it's preceded by0
.)u
Print decimal unsigned int
.f
,F
double
in normal (fixed-point) notation.f
andF
only differs in how the strings for an infinite number or NaN are printed (inf
,infinity
andnan
forf
;INF
,INFINITY
andNAN
forF
).e
,E
double
value in standard form ([-
]d.ddde
[+
/-
]ddd). AnE
conversion uses the letterE
(rather thane
) to introduce the exponent. The exponent always contains at least two digits; if the value is zero, the exponent is00
. In Windows, the exponent contains three digits by default, e.g.1.5e002
, but this can be altered by Microsoft-specific_set_output_format
function.g
,G
double
in either normal or exponential notation, whichever is more appropriate for its magnitude.g
uses lower-case letters,G
uses upper-case letters. This type differs slightly from fixed-point notation in that insignificant zeroes to the right of the decimal point are not included. Also, the decimal point is not included on whole numbers.x
,X
unsigned int
as a hexadecimal number.x
uses lower-case letters andX
uses upper-case.o
unsigned int
in octal.s
null-terminated string. c
char
(character).p
void *
(pointer to void) in an implementation-defined format.a
,A
double
in hexadecimal notation, starting with0x
or0X
.a
uses lower-case letters,A
uses upper-case letters.[1][2] (C++11 iostreams have ahexfloat
that works the same).n
Print nothing, but writes the number of characters successfully written so far into an integer pointer parameter.
Java: indicates a platform neutral newline/carriage return.[3]
Note: This can be utilized in Uncontrolled format string exploits.
- ↑ Template:cite web
- ↑
"printf"
(
%a
added in C99) - ↑ Template:cite web