Format Specification Fields: printf and wprintf Functions

A format specification, which consists of optional and required fields, has the following form:

%[flags] [width] [.precision] [{h | l | I64 | L}]type

Each field of the format specification is a single character or a number signifying a particular format option. The simplest format specification contains only the percent sign and a type character (for example, %s). If a percent sign is followed by a character that has no meaning as a format field, the character is copied to stdout. For example, to print a percent-sign character, use %%.

The optional fields, which appear before the type character, control other aspects of the formatting, as follows:

type

Required character that determines whether the associated argument is interpreted as a character, a string, or a number (see Table R.3).

flags

Optional character or characters that control justification of output and printing of signs, blanks, decimal points, and octal and hexadecimal prefixes (see Table R.4). More than one flag can appear in a format specification.

width

Optional number that specifies the minimum number of characters output. (See printf Width Specification.)

precision

Optional number that specifies the maximum number of characters printed for all or part of the output field, or the minimum number of digits printed for integer values (see Table R.5).

h | l | I64 | L

Optional prefixes to type-that specify the size of argument (see Table R.6).