C Language Formatted Input/Output Conversion Specifiers for printing
Example
| Conversion Specifier | Type of Argument | Description |
|---|---|---|
i, d | int | prints decimal |
u | unsigned int | prints decimal |
o | unsigned int | prints octal |
x | unsigned int | prints hexadecimal, lower-case |
X | unsigned int | prints hexadecimal, upper-case |
f | double | prints float with a default precision of 6, if no precision is given (lower-case used for special numbers nan and inf or infinity) |
F | double | prints float with a default precision of 6, if no precision is given (upper-case used for special numbers NAN and INF or INFINITY) |
e | double | prints float with a default precision of 6, if no precision is given, using scientific notation using mantissa/exponent; lower-case exponent and special numbers |
E | double | prints float with a default precision of 6, if no precision is given, using scientific notation using mantissa/exponent; upper-case exponent and special numbers |
g | double | uses either f or e [see below] |
G | double | uses either F or E [see below] |
a | double | prints hexadecimal, lower-case |
A | double | prints hexadecimal, upper-case |
c | char | prints single character |
s | char* | prints string of characters up to a NUL terminator, or truncated to length given by precision, if specified |
p | void* | prints void-pointer value; a nonvoid-pointer should be explicitly converted ("cast") to void*; pointer to object only, not a function-pointer |
% | n/a | prints the % character |
n | int * | write the number of bytes printed so far into the int pointed at. |
Note that length modifiers can be applied to %n (e.g. %hhn indicates that a following n conversion specifier applies to a pointer to a signed char
argument, according to the ISO/IEC 9899:2011 §7.21.6.1 ¶7).
Note that the floating point conversions apply to types float and double because of default promotion rules — §6.5.2.2 Function calls, ¶7 The ellipsis notation in a function prototype declarator causes
argument type conversion to stop after the last declared parameter. The default argument
promotions are performed on trailing arguments.) Thus, functions such as printf() are only ever passed double values, even if the variable referenced is of type float.
With the g and G formats, the choice between e and f (or E and F) notation is documented in the C standard and in the POSIX specification for printf():
The double argument representing a floating-point number shall be converted in the style
fore(or in the styleForEin the case of aGconversion specifier), depending on the value converted and the precision. LetPequal the precision if non-zero, 6 if the precision is omitted, or 1 if the precision is zero. Then, if a conversion with styleEwould have an exponent ofX:
- If P > X >= -4, the conversion shall be with style
f(orF) and precisionP - (X+1).- Otherwise, the conversion shall be with style
e(orE) and precisionP - 1.
Finally, unless the '#' flag is used, any trailing zeros shall be removed from the fractional portion of the result and the decimal-point character shall be removed if there is no fractional portion remaining.
