SPRINTF(3) NEWLIB SPRINTF(3)NAME
4.60 `sprintf', `fprintf', `printf', `snprintf', `asprintf',
`asnprintf'--format output
SYNOPSIS
#include <stdio.h>
int printf(const char *FORMAT, ...);
int fprintf(FILE *FD, const char *FORMAT, ...);
int sprintf(char *STR, const char *FORMAT, ...);
int snprintf(char *STR, size_t SIZE, const char *FORMAT,
...);
int asprintf(char **STRP, const char *FORMAT, ...);
char *asnprintf(char *STR, size_t *SIZE, const char *FORMAT,
...);
int _printf_r(struct _reent *PTR, const char *FORMAT, ...);
int _fprintf_r(struct _reent *PTR, FILE *FD,
const char *FORMAT, ...);
int _sprintf_r(struct _reent *PTR, char *STR,
const char *FORMAT, ...);
int _snprintf_r(struct _reent *PTR, char *STR, size_t SIZE,
const char *FORMAT, ...);
int _asprintf_r(struct _reent *PTR, char **STRP,
const char *FORMAT, ...);
char *_asnprintf_r(struct _reent *PTR, char *STR,
size_t *SIZE, const char *FORMAT, ...);
DESCRIPTION
`printf' accepts a series of arguments, applies to each a format speci‐
fier from `*FORMAT', and writes the formatted data to `stdout', without
a terminating NUL character. The behavior of `printf' is undefined if
there are not enough arguments for the format. `printf' returns when
it reaches the end of the format string. If there are more arguments
than the format requires, excess arguments are ignored.
`fprintf' is like `printf', except that output is directed to the
stream FD rather than `stdout'.
`sprintf' is like `printf', except that output is directed to the
buffer STR, and a terminating NUL is output. Behavior is undefined if
more output is generated than the buffer can hold.
`snprintf' is like `sprintf', except that output is limited to at
most SIZE bytes, including the terminating `NUL'. As a special case,
if SIZE is 0, STR can be NULL, and `snprintf' merely calculates how
many bytes would be printed.
`asprintf' is like `sprintf', except that the output is stored in a
dynamically allocated buffer, PSTR, which should be freed later with
`free'.
`asnprintf' is like `sprintf', except that the return type is either
the original STR if it was large enough, or a dynamically allocated
string if the output exceeds *SIZE; the length of the result is
returned in *SIZE. When dynamic allocation occurs, the contents of the
original STR may have been modified.
For `sprintf', `snprintf', and `asnprintf', the behavior is unde‐
fined if the output `*STR' overlaps with one of the arguments. Behav‐
ior is also undefined if the argument for `%n' within `*FORMAT' over‐
laps another argument.
FORMAT is a pointer to a character string containing two types of
objects: ordinary characters (other than `%'), which are copied
unchanged to the output, and conversion specifications, each of which
is introduced by `%'. (To include `%' in the output, use `%%' in the
format string.) A conversion specification has the following form:
%[POS][FLAGS][WIDTH][.PREC][SIZE]TYPE
The fields of the conversion specification have the following mean‐
ings:
* POS
Conversions normally consume arguments in the order that they are
presented. However, it is possible to consume arguments out of
order, and reuse an argument for more than one conversion
specification (although the behavior is undefined if the same
argument is requested with different types), by specifying POS,
which is a decimal integer followed by '$'. The integer must be
between 1 and <NL_ARGMAX> from limits.h, and if argument `%n$' is
requested, all earlier arguments must be requested somewhere
within FORMAT. If positional parameters are used, then all
conversion specifications except for `%%' must specify a position.
This positional parameters method is a POSIX extension to the C
standard definition for the functions.
* FLAGS
FLAGS is an optional sequence of characters which control output
justification, numeric signs, decimal points, trailing zeros, and
octal and hex prefixes. The flag characters are minus (`-'), plus
(`+'), space ( ), zero (`0'), sharp (`#'), and quote (`''). They
can appear in any combination, although not all flags can be used
for all conversion specification types.
`''
A POSIX extension to the C standard. However, this
implementation presently treats it as a no-op, which is the
default behavior for the C locale, anyway. (If it did what
it is supposed to, when TYPE were `i', `d', `u', `f', `F',
`g', or `G', the integer portion of the conversion would be
formatted with thousands' grouping wide characters.)
`-'
The result of the conversion is left justified, and the right
is padded with blanks. If you do not use this flag, the
result is right justified, and padded on the left.
`+'
The result of a signed conversion (as determined by TYPE of
`d', `i', `a', `A', `e', `E', `f', `F', `g', or `G') will
always begin with a plus or minus sign. (If you do not use
this flag, positive values do not begin with a plus sign.)
`" " (space)'
If the first character of a signed conversion specification
is not a sign, or if a signed conversion results in no
characters, the result will begin with a space. If the space
( ) flag and the plus (`+') flag both appear, the space flag
is ignored.
`0'
If the TYPE character is `d', `i', `o', `u', `x', `X', `a',
`A', `e', `E', `f', `F', `g', or `G': leading zeros are used
to pad the field width (following any indication of sign or
base); no spaces are used for padding. If the zero (`0') and
minus (`-') flags both appear, the zero (`0') flag will be
ignored. For `d', `i', `o', `u', `x', and `X' conversions,
if a precision PREC is specified, the zero (`0') flag is
ignored.
Note that `0' is interpreted as a flag, not as the beginning
of a field width.
`#'
The result is to be converted to an alternative form,
according to the TYPE character:
`o'
Increases precision to force the first digit of the
result to be a zero.
`x'
A non-zero result will have a `0x' prefix.
`X'
A non-zero result will have a `0X' prefix.
`a, A, e, E, f, or F'
The result will always contain a decimal point even if
no digits follow the point. (Normally, a decimal point
appears only if a digit follows it.) Trailing zeros are
removed.
`g or G'
The result will always contain a decimal point even if
no digits follow the point. Trailing zeros are not
removed.
`all others'
Undefined.
* WIDTH
WIDTH is an optional minimum field width. You can either specify
it directly as a decimal integer, or indirectly by using instead
an asterisk (`*'), in which case an `int' argument is used as the
field width. If positional arguments are used, then the width
must also be specified positionally as `*m$', with m as a decimal
integer. Negative field widths are treated as specifying the
minus (`-') flag for left justfication, along with a positive
field width. The resulting format may be wider than the specified
width.
* PREC
PREC is an optional field; if present, it is introduced with ``.''
(a period). You can specify the precision either directly as a
decimal integer or indirectly by using an asterisk (`*'), in which
case an `int' argument is used as the precision. If positional
arguments are used, then the precision must also be specified
positionally as `*m$', with m as a decimal integer. Supplying a
negative precision is equivalent to omitting the precision. If
only a period is specified the precision is zero. The effect
depends on the conversion TYPE.
`d, i, o, u, x, or X'
Minimum number of digits to appear. If no precision is
given, defaults to 1.
`a or A'
Number of digits to appear after the decimal point. If no
precision is given, the precision defaults to the minimum
needed for an exact representation.
`e, E, f or F'
Number of digits to appear after the decimal point. If no
precision is given, the precision defaults to 6.
`g or G'
Maximum number of significant digits. A precision of 0 is
treated the same as a precision of 1. If no precision is
given, the precision defaults to 6.
`s or S'
Maximum number of characters to print from the string. If no
precision is given, the entire string is printed.
`all others'
undefined.
* SIZE
SIZE is an optional modifier that changes the data type that the
corresponding argument has. Behavior is unspecified if a size is
given that does not match the TYPE.
`hh'
With `d', `i', `o', `u', `x', or `X', specifies that the
argument should be converted to a `signed char' or `unsigned
char' before printing.
With `n', specifies that the argument is a pointer to a
`signed char'.
`h'
With `d', `i', `o', `u', `x', or `X', specifies that the
argument should be converted to a `short' or `unsigned short'
before printing.
With `n', specifies that the argument is a pointer to a
`short'.
`l'
With `d', `i', `o', `u', `x', or `X', specifies that the
argument is a `long' or `unsigned long'.
With `c', specifies that the argument has type `wint_t'.
With `s', specifies that the argument is a pointer to
`wchar_t'.
With `n', specifies that the argument is a pointer to a
`long'.
With `a', `A', `e', `E', `f', `F', `g', or `G', has no effect
(because of vararg promotion rules, there is no need to
distinguish between `float' and `double').
`ll'
With `d', `i', `o', `u', `x', or `X', specifies that the
argument is a `long long' or `unsigned long long'.
With `n', specifies that the argument is a pointer to a `long
long'.
`j'
With `d', `i', `o', `u', `x', or `X', specifies that the
argument is an `intmax_t' or `uintmax_t'.
With `n', specifies that the argument is a pointer to an
`intmax_t'.
`z'
With `d', `i', `o', `u', `x', or `X', specifies that the
argument is a `size_t'.
With `n', specifies that the argument is a pointer to a
`size_t'.
`t'
With `d', `i', `o', `u', `x', or `X', specifies that the
argument is a `ptrdiff_t'.
With `n', specifies that the argument is a pointer to a
`ptrdiff_t'.
`L'
With `a', `A', `e', `E', `f', `F', `g', or `G', specifies
that the argument is a `long double'.
* TYPE
TYPE specifies what kind of conversion `printf' performs. Here is
a table of these:
`%'
Prints the percent character (`%').
`c'
Prints ARG as single character. If the `l' size specifier is
in effect, a multibyte character is printed.
`C'
Short for `%lc'. A POSIX extension to the C standard.
`s'
Prints the elements of a pointer to `char' until the
precision or a null character is reached. If the `l' size
specifier is in effect, the pointer is to an array of
`wchar_t', and the string is converted to multibyte
characters before printing.
`S'
Short for `%ls'. A POSIX extension to the C standard.
`d or i'
Prints a signed decimal integer; takes an `int'. Leading
zeros are inserted as necessary to reach the precision. A
value of 0 with a precision of 0 produces an empty string.
`D'
Newlib extension, short for `%ld'.
`o'
Prints an unsigned octal integer; takes an `unsigned'.
Leading zeros are inserted as necessary to reach the
precision. A value of 0 with a precision of 0 produces an
empty string.
`O'
Newlib extension, short for `%lo'.
`u'
Prints an unsigned decimal integer; takes an `unsigned'.
Leading zeros are inserted as necessary to reach the
precision. A value of 0 with a precision of 0 produces an
empty string.
`U'
Newlib extension, short for `%lu'.
`x'
Prints an unsigned hexadecimal integer (using `abcdef' as
digits beyond `9'); takes an `unsigned'. Leading zeros are
inserted as necessary to reach the precision. A value of 0
with a precision of 0 produces an empty string.
`X'
Like `x', but uses `ABCDEF' as digits beyond `9'.
`f'
Prints a signed value of the form `[-]9999.9999', with the
precision determining how many digits follow the decimal
point; takes a `double' (remember that `float' promotes to
`double' as a vararg). The low order digit is rounded to
even. If the precision results in at most DECIMAL_DIG
digits, the result is rounded correctly; if more than
DECIMAL_DIG digits are printed, the result is only guaranteed
to round back to the original value.
If the value is infinite, the result is `inf', and no zero
padding is performed. If the value is not a number, the
result is `nan', and no zero padding is performed.
`F'
Like `f', but uses `INF' and `NAN' for non-finite numbers.
`e'
Prints a signed value of the form `[-]9.9999e[+|-]999'; takes
a `double'. The digit before the decimal point is non-zero
if the value is non-zero. The precision determines how many
digits appear between `.' and `e', and the exponent always
contains at least two digits. The value zero has an exponent
of zero. If the value is not finite, it is printed like `f'.
`E'
Like `e', but using `E' to introduce the exponent, and like
`F' for non-finite values.
`g'
Prints a signed value in either `f' or `e' form, based on the
given value and precision--an exponent less than -4 or
greater than the precision selects the `e' form. Trailing
zeros and the decimal point are printed only if necessary;
takes a `double'.
`G'
Like `g', except use `F' or `E' form.
`a'
Prints a signed value of the form `[-]0x1.ffffp[+|-]9'; takes
a `double'. The letters `abcdef' are used for digits beyond
`9'. The precision determines how many digits appear after
the decimal point. The exponent contains at least one digit,
and is a decimal value representing the power of 2; a value
of 0 has an exponent of 0. Non-finite values are printed
like `f'.
`A'
Like `a', except uses `X', `P', and `ABCDEF' instead of lower
case.
`n'
Takes a pointer to `int', and stores a count of the number of
bytes written so far. No output is created.
`p'
Takes a pointer to `void', and prints it in an
implementation-defined format. This implementation is
similar to `%#tx'), except that `0x' appears even for the
NULL pointer.
`_printf_r', `_fprintf_r', `_asprintf_r', `_sprintf_r',
`_snprintf_r', `_asnprintf_r' are simply reentrant versions of the
functions above.
RETURNS
On success, `sprintf' and `asprintf' return the number of bytes in the
output string, except the concluding `NUL' is not counted. `snprintf'
returns the number of bytes that would be in the output string, except
the concluding `NUL' is not counted. `printf' and `fprintf' return the
number of characters transmitted. `asnprintf' returns the original STR
if there was enough room, otherwise it returns an allocated string.
If an error occurs, the result of `printf', `fprintf', `snprintf',
and `asprintf' is a negative value, and the result of `asnprintf' is
NULL. No error returns occur for `sprintf'. For `printf' and
`fprintf', `errno' may be set according to `fputc'. For `asprintf' and
`asnprintf', `errno' may be set to ENOMEM if allocation fails, and for
`snprintf', `errno' may be set to EOVERFLOW if SIZE or the output
length exceeds INT_MAX.
*Bugs*
The ""' (quote) flag does not work when locale's thousands_sep is not
empty.
PORTABILITY
ANSI C requires `printf', `fprintf', `sprintf', and `snprintf'.
`asprintf' and `asnprintf' are newlib extensions.
The ANSI C standard specifies that implementations must support at
least formatted output of up to 509 characters. This implementation
has no inherent limit.
Depending on how newlib was configured, not all format specifiers
are supported.
Supporting OS subroutines required: `close', `fstat', `isatty',
`lseek', `read', `sbrk', `write'.
SEE ALSOsprintf is part of the library. The full documentation for is main‐
tained as a Texinfo manual. If info and are properly installed at your
site, the command
info
will give you access to the complete manual.
NEWLIB April 2010 SPRINTF(3)
