CONTENTS

LIBRARY

SYNOPSIS

DESCRIPTION

These functions write the output under the control of a format string that specifies how subsequent arguments (or arguments accessed via the variable-length argument facilities of stdarg(3)) are converted for output.

These functions return the number of characters printed (not including the trailing ‘\0’ used to end output to strings).

The swprintf and vswprintf functions will fail if n or more wide characters were requested to be written,

The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the % character. The arguments must correspond properly (after type promotion) with the conversion specifier. After the %, the following appear in sequence:

• An optional field, consisting of a decimal digit string followed by a $, specifying the next argument to access. If this field is not provided, the argument following the last argument accessed will be used. Arguments are numbered starting at 1. If unaccessed arguments in the format string are interspersed with ones that are accessed the results will be indeterminate.
• Zero or more of the following flags:

  '#'	The value should be converted to an "alternate form". For c, d, i, n, p, s, and u conversions, this option has no effect. For o conversions, the precision of the number is increased to force the first character of the output string to a zero (except if a zero value is printed with an explicit precision of zero). For x and X conversions, a non-zero result has the string ‘0x’ (or ‘0X’ for X conversions) prepended to it. For a, A, e, E, f, F, g, and G conversions, the result will always contain a decimal point, even if no digits follow it (normally, a decimal point appears in the results of those conversions only if a digit follows). For g and G conversions, trailing zeros are not removed from the result as they would otherwise be.
  '0(zero)'	Zero padding. For all conversions except n, the converted value is padded on the left with zeros rather than blanks. If a precision is given with a numeric conversion ( d, i, o, u, i, x, and X), the 0 flag is ignored.
  '-'	A negative field width flag; the converted value is to be left adjusted on the field boundary. Except for n conversions, the converted value is padded on the right with blanks, rather than on the left with blanks or zeros. A - overrides a 0 if both are given.
  '" "(space)'	A blank should be left before a positive number produced by a signed conversion ( a, A, d, e, E, f, F, g, G, or i).
  '+'	A sign must always be placed before a number produced by a signed conversion. A + overrides a space if both are used.
  '’'	Decimal conversions ( d, u, or i) or the integral portion of a floating point conversion ( f or F) should be grouped and separated by thousands using the non-monetary separator returned by localeconv(3).

• An optional decimal digit string specifying a minimum field width. If the converted value has fewer characters than the field width, it will be padded with spaces on the left (or right, if the left-adjustment flag has been given) to fill out the field width.
• An optional precision, in the form of a period . followed by an optional digit string. If the digit string is omitted, the precision is taken as zero. This gives the minimum number of digits to appear for d, i, o, u, x, and X conversions, the number of digits to appear after the decimal-point for a, A, e, E, f, and F conversions, the maximum number of significant digits for g and G conversions, or the maximum number of characters to be printed from a string for s conversions.
• An optional length modifier, that specifies the size of the argument. The following length modifiers are valid for the d, i, n, o, u, x, or X conversion:

  Modifier d, i o, u, x, X n hh Vt "signed char" Vt "unsigned char" Vt "signed char *" h Vt short Vt "unsigned short" Vt "short *" l (ell) Vt long Vt "unsigned long" Vt "long *" ll (ell ell) Vt "long long" Vt "unsigned long long" Vt "long long *" j Vt intmax_t Vt uintmax_t Vt "intmax_t *" t Vt ptrdiff_t (see note) Vt "ptrdiff_t *" z (see note) Vt size_t (see note) q (deprecated) Vt quad_t Vt u_quad_t Vt "quad_t *"

  Note: the t modifier, when applied to a o, u, x, or X conversion, indicates that the argument is of an unsigned type equivalent in size to a
  .Vt ptrdiff_t . The z modifier, when applied to a d or i conversion, indicates that the argument is of a signed type equivalent in size to a
  .Vt size_t . Similarly, when applied to an n conversion, it indicates that the argument is a pointer to a signed type equivalent in size to a
  .Vt size_t .

  The following length modifier is valid for the a, A, e, E, f, F, g, or G conversion:

  Modifier a, A, e, E, f, F, g, G L Vt "long double"

  The following length modifier is valid for the c or s conversion:

  Modifier c s l (ell) Vt wint_t Vt "wchar_t *"

• A character that specifies the type of conversion to be applied.

A field width or precision, or both, may be indicated by an asterisk ‘*’ or an asterisk followed by one or more decimal digits and a ‘$’ instead of a digit string. In this case, an
.Vt int argument supplies the field width or precision. A negative field width is treated as a left adjustment flag followed by a positive field width; a negative precision is treated as though it were missing. If a single format directive mixes positional (nn$) and non-positional arguments, the results are undefined.

The conversion specifiers and their meanings are:

The decimal point character is defined in the program’s locale (category LC_NUMERIC).

SEE ALSO

STANDARDS