Collapse the table of content
Expand the table of content
Important This document may not represent best practices for current development, links to downloads and other resources may no longer be valid. Current recommended version can be found here. ArchiveDisclaimer


Enable or disable support of the %n format in printf, _printf_l, wprintf, _wprintf_l-family functions.

int _set_printf_count_output(
   int enable



A non-zero value to enable %n support, 0 to disable %n support.

The state of %n support before calling this function: non-zero if %n support was enabled, 0 if it was disabled.

Because of security reasons, support for the %n format specifier is disabled by default in printf and all its variants. If %n is encountered in a printf format specification, the default behavior is to invoke the invalid parameter handler as described in Parameter Validation. Calling _set_printf_count_output with a non-zero argument will cause printf-family functions to interpret %n as described in printf Type Field Characters.

Routine Required header Compatibility



ANSI, Windows 95, Windows 98, Windows 98 Second Edition, Windows Millennium Edition, Windows NT 4.0, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003

For additional compatibility information, see Compatibility in the Introduction.

// crt_set_printf_count_output.c
#include <stdio.h>

int main()
   int e;
   int i;
   e = _set_printf_count_output( 1 );
   printf( "%%n support was %sabled.\n",
        e ? "en" : "dis" );
   printf( "%%n support is now %sabled.\n",
        _get_printf_count_output() ? "en" : "dis" );
   printf( "12345%n6789\n", &i ); // %n format should set i to 5
   printf( "i = %d\n", i );

%n support was disabled.
%n support is now enabled.
i = 5

Not applicable. To call the standard C function, use PInvoke. For more information, see Platform Invoke Examples.

© 2015 Microsoft