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vprintf, vfprintf, vsprintf, vsnprintf

From cppreference.com
< c‎ | io

Defined in header <stdio.h>
(1)
int vprintf( const char          *format, va_list vlist );
(until C99)
int vprintf( const char *restrict format, va_list vlist );
(since C99)
(2)
int vfprintf( FILE          *stream, const char          *format,
              va_list vlist );
(until C99)
int vfprintf( FILE *restrict stream, const char *restrict format,
              va_list vlist );
(since C99)
(3)
int vsprintf( char          *buffer, const char          *format,
              va_list vlist );
(until C99)
int vsprintf( char *restrict buffer, const char *restrict format,
              va_list vlist );
(since C99)
int vsnprintf( char *restrict buffer, int buf_size,
               const char *restrict format, va_list vlist );
(4) (since C99)

Loads the data from the locations, defined by vlist, converts them to character string equivalents and writes the results to a variety of sinks.

1) Writes the results to stdout.
2) Writes the results to a file stream stream.
3) Writes the results to a character string buffer.
4) Writes the results to a character string buffer. At most buf_size characters are written. The resulting character string will be terminated with a null character, unless buf_size is zero.

Contents

[edit] Parameters

stream - output file stream to write to
buffer - pointer to a character string to write to
buf_size - maximum number of characters to write
format - pointer to a null-terminated character string specifying how to interpret the data.

The format string consists of ordinary characters (except %), which are copied unchanged into the output stream, and conversion specifications. Each conversion specification has the following format:

  • introductory % character
  • (optional) one or more flags that modify the behavior of the conversion:
  • -: the result of the conversion is left-justified within the field (by default it is right-justified)
  • +: the sign of signed conversions is always prepended to the result of the conversion (by default the result is preceded by minus only when it is negative)
  • space: if the result of a signed conversion does not start with a sign character, or is empty, space is prepended to the result. It is ignored if + flag is present.
  • # : alternative form of the conversion is performed. See the table below for exact effects.
  • 0 : for integer and floating point number conversions, leading zeros are used to pad the field instead of space characters. For floating point numbers it is ignored if the precision is explicitly specified. For other conversions using this flag results in undefined behavior. It is ignored if - flag is present.
  • (optional) integer value or * that specifies minimum field width. The result is padded with space characters (by default), if required, on the left when right-justified, or on the right if left-justified. In the case when * is used, the width is specified by an additional argument of type int. If the value of the argument is negative, it results with the - flag specified and positive field width.
  • (optional) . followed by integer number or * that specifies precision of the conversion. In the case when * is used, the precision is specified by an additional argument of type int. If the value of this argument is negative, it is ignored. See the table below for exact effects of precision.
  • (optional) length modifier that specifies the size of the argument
  • conversion format specifier

The following format specifiers are available:

Conversion
specifier
Explanation Argument type
length modifier hh h (none) l ll j z t L
% writes literal %. The full conversion specification must be %%. N/A N/A N/A N/A N/A N/A N/A N/A N/A
c writes a single character N/A N/A char wchar_t N/A N/A N/A N/A N/A
s
writes a character string.

Precision specifies the maximum number of bytes to be written.

N/A N/A char* wchar_t* N/A N/A N/A N/A N/A
d
i
converts a signed decimal integer in the style [-]dddd.

Precision specifies the minimum number of digits to appear. The default precision is 1.
If both the converted value and the precision are 0 the conversion results in no characters.

signed char
signed short
signed int
signed long
signed long long
N/A
o
converts a signed octal integer in the style [-]oooo.

Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are 0 the conversion results in no characters. In the alternative implementation precision is increased if necessary, to write one leading zero. In that case if both the converted value and the precision are 0, single 0 is written.

N/A
x
X
converts a signed hexadecimal integer in the style [-]hhhh.

For the x conversion letters abcdef are used.
For the X conversion letters ABCDEF are used.
Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are 0 the conversion results in no characters. In the alternative implementation 0x or 0X is prefixed to results if the converted value is nonzero.

unsigned char
unsigned short
unsigned int
unsigned long
unsigned long long
N/A
u
converts an unsigned decimal integer in the style dddd.

Precision specifies the minimum number of digits to appear. The default precision is 1. If both the converted value and the precision are 0 the conversion results in no characters.

N/A
f
F
converts floating-point number to the decimal notation in the style [-]ddd.ddd.

Precision specifies the minimum number of digits to appear after the decimal point character. The default precision is 6. In the alternative implementation decimal point character is written even if no digits follow it. For infinity and not-a-number conversion style see notes.

N/A N/A
double
double
N/A N/A N/A N/A
long double
e
E
converts floating-point number to the decimal exponent notation.

For the e conversion style [-]d.ddde±dd is used.
For the E conversion style [-]d.dddE±dd is used.
The exponent contains at least two digits, more digits are used only if necessary. If the value is 0, the exponent is also 0. Precision specifies the minimum number of digits to appear after the decimal point character. The default precision is 6. In the alternative implementation decimal point character is written even if no digits follow it. For infinity and not-a-number conversion style see notes.

N/A N/A N/A N/A N/A N/A
a
A
converts floating-point number to the hexadecimal exponent notation.

For the a conversion style [-]0xh.hhhp±d is used.
For the A conversion style [-]0Xh.hhhP±d is used.
The first hexadecimal digit is 0 if the argument is not a normalized floating point value. If the value is 0, the exponent is also 0. Precision specifies the minimum number of digits to appear after the decimal point character. The default precision is sufficient for exact representation of the value. In the alternative implementation decimal point character is written even if no digits follow it. For infinity and not-a-number conversion style see notes.

N/A N/A N/A N/A N/A N/A
g
G
converts floating-point number to decimal or decimal exponent notation depending on the value and the precision.

For the g conversion style conversion with style e or f will be performed.
For the G conversion style conversion with style E or F will be performed.
Let P equal the precision if nonzero, 6 if the precision is not specified, or 1 if the precision is 0. Then, if a conversion with style E would have an exponent of X:

  • if P > X ≥ −4, the conversion is with style f or F and precision P − 1 − X.
  • otherwise, the conversion is with style e or E and precision P − 1.

Unless alternative representation is requested the trailing zeros are removed, also the decimal point character is removed if no fractional part is left. For infinity and not-a-number conversion style see notes.

N/A N/A N/A N/A N/A N/A
n
returns the number of characters written so far by this call to the function.

The result is written to the value pointed to by the argument. The complete specification must be %n.

N/A N/A int* N/A N/A N/A N/A N/A N/A
p writes an implementation defined character sequence defining a pointer. N/A N/A void* N/A N/A N/A N/A N/A N/A
Notes:

The floating point conversion functions convert infinity to inf or infinity. Which one is used is implementation defined.
Not-a-number is converted to nan or nan(char_sequence). Which one is used is implementation defined.
The conversions F, E, G, A output INF, INFINITY, NAN instead.
The correct conversion specifiers for the fixed-width character types (std::int8_t, etc) are defined in the header <cinttypes>


vlist - variable argument list containing the data to print

[edit] Return value

1-3) The number of characters written if successful or negative value if an error occurred.
4) The number of characters written if successful or negative value if an error occurred. If the resulting string gets truncated due to buf_size limit, function returns the total number of characters (not including the terminating null-byte) which would have been written, if the limit was not imposed.

[edit] Example

Write from variables day, month, year to a null-terminated character string.

#include <stdio.h>
#include <stdarg.h>
 
void putdate (char *str, const char *format, ...)
{
  va_list args;
  va_start(args,format);
  vsprintf(str,format,args);
  va_end(args);
}
 
int main(void)
{
  int day=20, year=2012;
  char *month="June";
  char str[10];
  putdate(str,"%d %s %d", day,month,year);
  printf("summer solstice:  %s\n", str);
 
  return 0;
}

Possible output:

summer solstice:  20 June 2012

[edit] See also

prints formatted output to stdout, a file stream or a buffer
(function) [edit]
(C99)(C99)(C99)
reads formatted input from stdin, a file stream or a buffer
using variable argument list
(function) [edit]
C++ documentation for vprintf, vfprintf, vsprintf, vsnprintf