Printf

C programming language, the famous printf function prints the optional arguments under the control of the template string template to the stream stdout. It returns the number of characters printed, or a negative value if there occurred an output error.

Perl also has a printf function. Common Lisp has a format function which acts under the same principles as printf, but uses different characters for output conversion. The GLib library contains g_printf, an implementation of printf.

Output Conversions

Here is a table summarizing what all the different conversions do (in the C programming language, other versions might be different):

`%d', `%i' 

Print an integer as a signed decimal number. `%d' and `%i' are synonymous for output, but are different when used with scanf() function for input.

`%o' 

Print an integer as an unsigned octal number.

`%u' 

Print an integer as an unsigned decimal number.

`%x', `%X' 

Print an integer as an unsigned hexadecimal number. `%x' uses lower-case letters and `%X' uses upper-case.

`%f' 

Print a floating-point number in normal (fixed-point) notation.

`%e', `%E' 

Print a floating-point number in exponential notation. `%e' uses lower-case letters and `%E' uses upper-case.

`%g', `%G' 

Print a floating-point number in either normal or exponential notation, whichever is more appropriate for its magnitude. `%g' uses lower-case letters and `%G' uses upper-case.

`%a', `%A' 

Print a floating-point number in a hexadecimal fractional notation which the exponent to base 2 represented in decimal digits. `%a' uses lower-case letters and `%A' uses upper-case.

`%c' 

Print a single character.

`%lc' 

Print a single wide character.

`%C' 

This is an alias for `%lc'. (This is a non-standard Unix-specific extension.)

`%s' 

Print a string.

`%ls' 

Print a wide character string.

`%S' 

This is an alias for `%ls'. (This is a non-standard Unix-specific extension.)

`%p' 

Print the value of a pointer.

`%n' 

Get the number of characters printed so far. Note that this conversion specification never produces any output.

`%m' 

Print the string corresponding to the value of errno variable. (This is a non-standard GNU extension.)

`%%' 

Print a literal `%' character.

If the syntax of a conversion specification is invalid, unpredictable things will happen, so don't do this. If there aren't enough function arguments provided to supply values for all the conversion specifications in the template string, or if the arguments are not of the correct types, the results are unpredictable. If you supply more arguments than conversion specifications, the extra argument values are simply ignored; this is sometimes useful.

See also

• C standard library
• Format string attacks