sprintf(3C)
NAME
printf, fprintf, sprintf, snprintf - print formatted output
SYNOPSIS
#include <stdio.h>
int printf(const char *format, /* args*/ ...);
int fprintf(FILE *stream, const char *format, /* args*/
...);
int sprintf(char *s, const char *format, /* args*/ ...);
int snprintf(char *s, size_t n, const char *format, /*
args*/ ...);
DESCRIPTION
The printf() function places output on the standard output
stream stdout.
The fprintf() function places output on on the named output
stream stream.
The sprintf() function places output, followed by the null
byte (\0), in consecutive bytes starting at s; it is the
user's responsibility to ensure that enough storage is
available.
The snprintf() function is identical to sprintf() with the
addition of the argument n, which specifies the size of the
buffer referred to by s. The buffer is always terminated
with the null byte.
Each of these functions converts, formats, and prints its
arguments under control of the format. The format is a char-
acter string, beginning and ending in its initial shift
state, if any. The format is composed of zero or more
directives: ordinary characters, which are simply copied to
the output stream and conversion specifications, each of
which results in the fetching of zero or more arguments. The
results are undefined if there are insufficient arguments
for the format. If the format is exhausted while arguments
remain, the excess arguments are evaluated but are otherwise
ignored.
Conversions can be applied to the nth argument after the
format in the argument list, rather than to the next unused
argument. In this case, the conversion character % (see
below) is replaced by the sequence %n$, where n is a decimal
integer in the range [1, NL_ARGMAX], giving the position of
the argument in the argument list. This feature provides for
the definition of format strings that select arguments in an
order appropriate to specific languages (see the EXAMPLES
section).
In format strings containing the %n$ form of conversion
specifications, numbered arguments in the argument list can
be referenced from the format string as many times as
required.
In format strings containing the % form of conversion
specifications, each argument in the argument list is used
exactly once.
All forms of the printf() functions allow for the insertion
of a language-dependent radix character in the output
string. The radix character is defined by the program's
locale (category LC_NUMERIC). In the POSIX locale, or in a
locale where the radix character is not defined, the radix
character defaults to a period (.).
Conversion Specifications
Each conversion specification is introduced by the % charac-
ter or by the character sequence %n$, after which the fol-
lowing appear in sequence:
o An optional field, consisting of a decimal digit
string followed by a $, specifying the next argument
to be converted. If this field is not provided, the
args following the last argument converted will be
used.
o Zero or more flags (in any order), which modify the
meaning of the conversion specification.
o An optional minimum field width. If the converted
value has fewer bytes than the field width, it will be
padded with spaces by default on the left; it will be
padded on the right, if the left-adjustment flag (-),
described below, is given to the field width. The
field width takes the form of an asterisk (*),
described below, or a decimal integer.
If the conversion character is s, a standard-
conforming application (see standards(5)) interprets
the field width as the minimum number of bytes to be
printed; an application that is not standard-
conforming interprets the field width as the minimum
number of columns of screen display. For an applica-
tion that is not standard-conforming, %10s means if
the converted value has a screen width of 7 columns, 3
spaces would be padded on the right.
If the format is %ws, then the field width should be inter-
preted as the minimum number of columns of screen display.
o An optional precision that gives the minimum number of
digits to appear for the d, i, o, u, x, and X conver-
sions (the field is padded with leading zeros); the
number of digits to appear after the radix character
for the e, E, and f conversions, the maximum number of
significant digits for the g and G conversions; or the
maximum number of bytes to be printed from a string in
s and S conversions. The precision takes the form of
a period (.) followed either by an asterisk (*),
described below, or an optional decimal digit string,
where a null digit string is treated as 0. If a pre-
cision appears with any other conversion character,
the behavior is undefined.
If the conversion character is s or S, a standard-
conforming application (see standards(5)) interprets
the precision as the maximum number of bytes to be
written; an application that is not standard-
conforming interprets the precision as the maximum
number of columns of screen display. For an applica-
tion that is not standard-conforming, %.5s would print
only the portion of the string that would display in 5
screen columns. Only complete characters are written.
For %ws, the precision should be interpreted as the maximum
number of columns of screen display. The precision takes the
form of a period (.) followed by a decimal digit string; a
null digit string is treated as zero. Padding specified by
the precision overrides the padding specified by the field
width.
o An optional h specifies that a following d, i, o, u,
x, or X conversion character applies to a type short
int or type unsigned short int argument (the argument
will be promoted according to the integral promotions,
and its value converted to type short int or unsigned
short int before printing); an optional h specifying
that a following n conversion character applies to a
pointer to a type short int argument; an optional l
(ell) specifying that a following d, i, o, u, x, or
X conversion character applies to a type long int or
unsigned long int argument; an optional l (ell)
specifying that a following n conversion character
applies to a pointer to a type long int argument; an
optional
ll (ell ell) specifying that a following d, i, o,
u, x, or X conversion character applies to a type
long long or unsigned long long argument; an optional
ll (ell ell) specifying that a following n conversion
character applies to a pointer to a long long argu-
ment; or an optional L specifying that a following e,
E, f, g, or G conversion character applies to a type
long double argument. If an h, l, ll, or L appears
with any other conversion character, the behavior is
undefined.
o An optional l (ell) specifying that a following c
conversion character applies to a wint_t argument; an
optional l (ell) specifying that a following s conver-
sion character applies to a pointer to a wchar_t
argument.
o A conversion character (see below) that indicates the
type of conversion to be applied.
A field width, or precision, or both may be indicated by an
asterisk (*) . In this case, an argument of type int sup-
plies the field width or precision. Arguments specifying
field width, or precision, or both must appear in that order
before the argument, if any, to be converted. A negative
field width is taken as a - flag followed by a positive
field width. A negative precision is taken as if the preci-
sion were omitted. In format strings containing the %n$ form
of a conversion specification, a field width or precision
may be indicated by the sequence *m$, where m is a decimal
integer in the range [1, NL_ARGMAX] giving the position in
the argument list (after the format argument) of an integer
argument containing the field width or precision, for exam-
ple:
printf("%1$d:%2$.*3$d:%4$.*3$d\n", hour, min, precision, sec);
The format can contain either numbered argument specifica-
tions (that is, %n$ and *m$), or unnumbered argument specif-
ications (that is, % and *), but normally not both. The only
exception to this is that %% can be mixed with the %n$ form.
The results of mixing numbered and unnumbered argument
specifications in a format string are undefined. When num-
bered argument specifications are used, specifying the Nth
argument requires that all the leading arguments, from the
first to the (N-1)th, are specified in the format string.
Flag Characters
The flag characters and their meanings are:
' The integer portion of the result of a decimal conver-
sion (%i, %d, %u, %f, %g, or %G) will be formatted
with thousands' grouping characters. For other conver-
sions the behavior is undefined. The non-monetary
grouping character is used.
- The result of the conversion will be left-justified
within the field. The conversion will be right-
justified if this flag is not specified.
+ The result of a signed conversion will always begin
with a sign (+ or -). The conversion will begin with a
sign only when a negative value is converted if this
flag is not specified.
space If the first character of a signed conversion is not a
sign or if a signed conversion results in no charac-
ters, a space will be placed before the result. This
means that if the space and + flags both appear, the
space flag will be ignored.
# The value is to be converted to an alternate form. For
c, d, i, s, and u conversions, the flag has no effect.
For an o conversion, it increases the precision (if
necessary) to force the first digit of the result to
be a zero. For x or X conversion, a non-zero result
will have 0x (or 0X) prepended to it. For e, E, f, g,
and G conversions, the result will always contain a
radix character, even if no digits follow the radix
character. Without this flag, the radix character
appears in the result of these conversions only if a
digit follows it. For g and G conversions, trailing
zeros will not be removed from the result as they nor-
mally are.
0 For d, i, o, u, x, X, e, E, f, g, and G conversions,
leading zeros (following any indication of sign or
base) are used to pad to the field width; no space
padding is performed. If the 0 and - flags both
appear, the 0 flag will be ignored. For d, i, o, u, x,
and X conversions, if a precision is specified, the 0
flag will be ignored. If the 0 and ' flags both
appear, the grouping characters are inserted before
zero padding. For other conversions, the behavior is
undefined.
Conversion Characters
Each conversion character results in fetching zero or more
arguments. The results are undefined if there are insuffi-
cient arguments for the format. If the format is exhausted
while arguments remain, the excess arguments are ignored.
The conversion characters and their meanings are:
d,i The int argument is converted to a signed decimal in
the style [-]dddd. The precision specifies the minimum
number of digits to appear; if the value being con-
verted can be represented in fewer digits, it will be
expanded with leading zeros. The default precision is
1. The result of converting 0 with an explicit preci-
sion of 0 is no characters.
o The unsigned int argument is converted to unsigned
octal format in the style dddd. The precision speci-
fies the minimum number of digits to appear; if the
value being converted can be represented in fewer
digits, it will be expanded with leading zeros. The
default precision is 1. The result of converting 0
with an explicit precision of 0 is no characters.
u The unsigned int argument is converted to unsigned
decimal format in the style dddd. The precision speci-
fies the minimum number of digits to appear; if the
value being converted can be represented in fewer
digits, it will be expanded with leading zeros. The
default precision is 1. The result of converting 0
with an explicit precision of 0 is no characters.
x The unsigned int argument is converted to unsigned
hexadecimal format in the style dddd; the letters
abcdef are used. The precision specifies the minimum
number of digits to appear; if the value being con-
verted can be represented in fewer digits, it will be
expanded with leading zeros. The default precision is
1. The result of converting 0 with an explicit preci-
sion of 0 is no characters.
X Behaves the same as the x conversion character except
that letters ABCDEF are used instead of abcdef.
f The double argument is converted to decimal notation
in the style [-]ddd.ddd, where the number of digits
after the radix character (see setlocale(3C)) is equal
to the precision specification. If the precision is
missing it is taken as 6; if the precision is expli-
citly 0 and the # flag is not specified, no radix
character appears. If a radix character appears, at
least 1 digit appears before it. The value is rounded
to the appropriate number of digits.
e,E The double argument is converted to the style
[-]d.ddde_dd, where there is one digit before the
radix character (which is non-zero if the argument is
non-zero) and the number of digits after it is equal
to the precision. When the precision is missing it is
taken as 6; if the precision is 0 and the # flag is
not specified, no radix character appears. The E
conversion character will produce a number with E
instead of e introducing the exponent. The exponent
always contains at least two digits. The value is
rounded to the appropriate number of digits.
g,G The double argument is printed in style f or e (or in
style E in the case of a G conversion character), with
the precision specifying the number of significant
digits. If an explicit precision is 0, it is taken as
1. The style used depends on the value converted:
style e (or E) will be used only if the exponent
resulting from the conversion is less than -4 or
greater than or equal to the precision. Trailing zeros
are removed from the fractional part of the result. A
radix character appears only if it is followed by a
digit.
c The int argument is converted to an unsigned char, and
the resulting byte is printed.
If an l (ell) qualifier is present, the wint_t argu-
ment is converted as if by an ls conversion specifica-
tion with no precision and an argument that points to
a two-element array of type wchar_t, the first element
of which contains the wint_t argument to the ls
conversion specification and the second element con-
tains a null wide-character.
C Same as lc.
wc The int argument is converted to a wide character
(wchar_t), and the resulting wide character is
printed.
s The argument must be a pointer to an array of char.
Bytes from the array are written up to (but not
including) any terminating null byte. If a precision
is specified, a standard-conforming application (see
standards(5)) will write only the number of bytes
specified by precision; an application that is not
standard-conforming will write only the portion of the
string that will display in the number of columns of
screen display specified by precision. If the preci-
sion is not specified, it is taken to be infinite, so
all bytes up to the first null byte are printed. An
argument with a null value will yield undefined
results.
If an l (ell) qualifier is present, the argument must
be a pointer to an array of type wchar_t. Wide-
characters from the array are converted to characters
(each as if by a call to the wcrtomb(3C) function,
with the conversion state described by an mbstate_t
object initialized to zero before the first wide-
character is converted) up to and including a
terminating null wide-character. The resulting char-
acters are written up to (but not including) the ter-
minating null character (byte). If no precision is
specified, the array must contain a null wide-
character. If a precision is specified, no more than
that many characters (bytes) are written (including
shift sequences, if any), and the array must contain a
null wide-character if, to equal the character
sequence length given by the precision, the function
would need to access a wide-character one past the end
of the array. In no case is a partial character writ-
ten.
S Same as ls.
ws The argument must be a pointer to an array of wchar_t.
Bytes from the array are written up to (but not
including) any terminating null character. If the pre-
cision is specified, only that portion of the wide-
character array that will display in the number of
columns of screen display specified by precision will
be written. If the precision is not specified, it is
taken to be infinite, so all wide characters up to the
first null character are printed. An argument with a
null value will yield undefined results.
p The argument must be a pointer to void. The value of
the pointer is converted to a set of sequences of
printable characters, which should be the same as the
set of sequences that are matched by the %p conversion
of the scanf(3C) function.
n The argument must be a pointer to an integer into
which is written the number of bytes written to the
output standard I/O stream so far by this call to one
of the printf() functions. No argument is converted.
% Print a %; no argument is converted. The entire
conversion specification must be %%.
If a conversion specification does not match one of the
above forms, the behavior is undefined.
If a floating-point value is the internal representation for
infinity, the output is [_]Infinity, where Infinity is
either Infinity or Inf, depending on the desired output
string length. Printing of the sign follows the rules
described above.
If a floating-point value is the internal representation for
"not-a-number," the output is [_]NaN. Printing of the sign
follows the rules described above.
In no case does a non-existent or small field width cause
truncation of a field; if the result of a conversion is
wider than the field width, the field is simply expanded to
contain the conversion result. Characters generated by
printf() and fprintf() are printed as if the putc(3C) func-
tion had been called.
The st_ctime and st_mtime fields of the file will be marked
for update between the call to a successful execution of
printf() or fprintf() and the next successful completion of
a call to fflush(3C) or fclose(3C) on the same stream or a
call to exit(3C) or abort(3C).
RETURN VALUES
The printf(), fprintf(), and sprintf() functions return the
number of bytes transmitted (excluding the terminating null
byte in the case of sprintf()).
The snprintf() function returns the number of characters
formatted, that is, the number of characters that would have
been written to the buffer if it were large enough. If the
value of n is 0 on a call to snprintf(), an unspecified
value less than 1 is returned.
Each function returns a negative value if an output error
was encountered.
ERRORS
For the conditions under which printf() and fprintf() will
fail and may fail, refer to fputc(3C) or fputwc(3C).
In addition, all forms of printf() may fail if:
EILSEQ
A wide-character code that does not correspond to a
valid character has been detected.
EINVAL
There are insufficient arguments.
In addition, printf() and fprintf() may fail if:
ENOMEM
Insufficient storage space is available.
USAGE
If the application calling the printf() functions has any
objects of type wint_t or wchar_t, it must also include the
header <wchar.h> to have these objects defined.
The sprintf() and snprintf() functions are MT-Safe in mul-
tithreaded applications. The printf() and fprintf()
functions can be used safely in multithreaded applications,
as long as setlocale(3C) is not being called to change the
locale.
Escape Character Sequences
It is common to use the following escape sequences built
into the C language when entering format strings for the
printf() functions, but these sequences are processed by the
C compiler, not by the printf() function.
\a Alert. Ring the bell.
\b Backspace. Move the printing position to one
character before the current position, unless the
current position is the start of a line.
\f Form feed. Move the printing position to the ini-
tial printing position of the next logical page.
\n Newline. Move the printing position to the start
of the next line.
\r Carriage return. Move the printing position to
the start of the current line.
\t Horizontal tab. Move the printing position to the
next implementation-defined horizontal tab posi-
tion on the current line.
\v Vertical tab. Move the printing position to the
start of the next implementation-defined vertical
tab position.
In addition, the C language supports character sequences of
the form
\octal-number
and
\hex-number
which translates into the character represented by the octal
or hexadecimal number. For example, if ASCII representations
are being used, the letter 'a' may be written as '\141' and
'Z' as '\132'. This syntax is most frequently used to
represent the null character as '\0'. This is exactly
equivalent to the numeric constant zero (0). Note that the
octal number does not include the zero prefix as it would
for a normal octal constant. To specify a hexadecimal
number, omit the zero so that the prefix is an 'x'
(uppercase 'X' is not allowed in this context). Support for
hexadecimal sequences is an ANSI extension. See stan-
dards(5).
EXAMPLES
Example 1: To print the language-independent date and time
format, the following statement could be used:
printf (format, weekday, month, day, hour, min);
For American usage, format could be a pointer to the string:
"%s, %s %d, %d:%.2d\n"
producing the message:
Sunday, July 3, 10:02
whereas for German usage, format could be a pointer to the
string:
"%1$s, %3$d. %2$s, %4$d:%5$.2d\n"
producing the message:
Sonntag, 3. Juli, 10:02
Example 2: To print a date and time in the form Sunday, July
3, 10:02, where weekday and month are pointers to null-
terminated strings:
printf("%s, %s %i, %d:%.2d", weekday, month, day, hour, min);
Example 3: To print pi to 5 decimal places:
printf("pi = %.5f", 4 * atan(1.0));
Default
Example 4: The following example applies only to applica-
tions which are not standard-conforming (see standards(5)).
To print a list of names in columns which are 20 characters
wide:
printf("%20s%20s%20s", lastname, firstname, middlename);
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| CSI | Enabled |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
| MT-Level | MT-Safe with exceptions |
|_____________________________|_____________________________|
SEE ALSO
exit(2), lseek(2), write(2), abort(3C), ecvt(3C), exit(3C),
fclose(3C), fflush(3C), fputwc(3C), putc(3C), scanf(3C),
setlocale(3C), stdio(3C), wcstombs(3C), wctomb(3C), attri-
butes(5), environ(5), standards(5)
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