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The latest version of this topic can be found at _set_printf_count_output.

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.

RoutineRequired header

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.