_fprintf_p, _fprintf_p_l, _ftprintf_p, _ftprintf_p_l, _fwprintf_p, _fwprintf_p_l

Prints formatted data to a stream.

For _ftprintf_p and _ftprintf_p_l, see Generic-text function mappings.

Syntax

int _fprintf_p(
   FILE *stream,
   const char *format [,
   argument ]...
);
int _fprintf_p_l(
   FILE *stream,
   const char *format,
   _locale_t locale [,
   argument ]...
);
int _fwprintf_p(
   FILE *stream,
   const wchar_t *format [,
   argument ]...
);
int _fwprintf_p_l(
   FILE *stream,
   const wchar_t *format,
   _locale_t locale [,
   argument ]...
);

Parameters

stream
Pointer to the FILE structure.

format
Format-control string.

argument
Optional arguments.

locale
The locale to use.

Return value

_fprintf_p and _fwprintf_p return the number of characters written or return a negative value when an output error occurs.

Remarks

_fprintf_p formats and prints a series of characters and values to the output stream. Each function argument (if any) is converted and output according to the corresponding format specification in format. For _fprintf_p, the format argument has the same syntax that it has in _printf_p. These functions support positional parameters, meaning that the order of the parameters used by the format string can be changed. For more information about positional parameters, see printf_p Positional Parameters.

_fwprintf_p is a wide-character version of _fprintf_p; in _fwprintf_p, format is a wide-character string. These functions behave identically if the stream is opened in ANSI mode. _fprintf_p doesn't currently support output into a UNICODE stream.

The versions of these functions with the _l suffix are identical except that they use the locale parameter passed in instead of the current locale.

Important

Ensure that format is not a user-defined string.

Starting in Windows 10 version 2004 (build 19041), the printf family of functions prints exactly representable floating point numbers according to the IEEE 754 rules for rounding. In previous versions of Windows, exactly representable floating point numbers ending in '5' would always round up. IEEE 754 states that they must round to the closest even digit (also known as "Banker's Rounding"). For example, both printf("%1.0f", 1.5) and printf("%1.0f", 2.5) should round to 2. Previously, 1.5 would round to 2 and 2.5 would round to 3. This change only affects exactly representable numbers. For example, 2.35 (which, when represented in memory, is closer to 2.35000000000000008) continues to round up to 2.4. Rounding done by these functions now also respects the floating point rounding mode set by fesetround. Previously, rounding always chose FE_TONEAREST behavior. This change only affects programs built using Visual Studio 2019 version 16.2 and later. To use the legacy floating point rounding behavior, link with 'legacy_stdio_float_rounding.obj`.

Like the non-secure versions (see fprintf, _fprintf_l, fwprintf, _fwprintf_l), these functions validate their parameters and invoke the invalid parameter handler, as described in Parameter validation, if either stream or format is a null pointer or if there are any unknown or badly formed formatting specifiers. If execution is allowed to continue, the functions return -1 and set errno to EINVAL.

Generic-text function mappings

The function in the tchar.h column maps to the function in the other columns depending on the character set that is defined at compile time.

tchar.h function	_UNICODE and _MBCS not defined	_MBCS defined	_UNICODE defined
_ftprintf_p	_fprintf_p	_fprintf_p	_fwprintf_p
_ftprintf_p_l	_fprintf_p_l	_fprintf_p_l	_fwprintf_p_l

For more information, see Format specification syntax.

Requirements

Function	Required header
_fprintf_p, _fprintf_p_l	<stdio.h>
_fwprintf_p, _fwprintf_p_l	<stdio.h> or <wchar.h>

For more compatibility information, see Compatibility.

Example

// crt_fprintf_p.c
// This program uses _fprintf_p to format various
// data and print it to the file named FPRINTF_P.OUT. It
// then displays FPRINTF_P.OUT on the screen using the system
// function to invoke the operating-system TYPE command.
//

#include <stdio.h>
#include <process.h>

int main( void )
{
    FILE    *stream = NULL;
    int     i = 10;
    double  fp = 1.5;
    char    s[] = "this is a string";
    char    c = '\n';

    // Open the file
    if ( fopen_s( &stream, "fprintf_p.out", "w" ) == 0)
    {
        // Format and print data
        _fprintf_p( stream, "%2$s%1$c", c, s );
        _fprintf_p( stream, "%d\n", i );
        _fprintf_p( stream, "%f\n", fp );

        // Close the file
        fclose( stream );
    }

    // Verify our data
    system( "type fprintf_p.out" );
}

this is a string
10
1.500000

See also

Stream I/O
_cprintf, _cprintf_l, _cwprintf, _cwprintf_l
fscanf, _fscanf_l, fwscanf, _fwscanf_l
sprintf, _sprintf_l, swprintf, _swprintf_l, __swprintf_l
printf_p Positional Parameters
_cprintf_p, _cprintf_p_l, _cwprintf_p, _cwprintf_p_l
_cprintf_s, _cprintf_s_l, _cwprintf_s, _cwprintf_s_l
printf_p Positional Parameters
fscanf_s, _fscanf_s_l, fwscanf_s, _fwscanf_s_l