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_CrtSetDebugFillThreshold

Retrieves or modifies the threshold controlling buffer-filling behavior in debug functions.

size_t _CrtSetDebugFillThreshold(
   size_t _NewThreshold
);

newThreshold

New threshold.

The previous threshold.

The debug versions of some security-enhanced CRT functions fill the buffer passed to them with a special character (0xFD). This helps to find cases where the incorrect size was passed to the function. Unfortunately, it also reduces performance. To improve performance, use _CrtSetDebugFillThreshold to disable buffer-filling for buffers larger than the threshold. A threshold of 0 will disable it for all buffers.

The default threshold is SIZE_T_MAX.

Here is a list of the affected functions.

Routine

Required header

_CrtSetDebugFillThreshold

<crtdbg.h>

For more compatibility information, see Compatibility in the Introduction.

Libraries

Debug versions of C run-time libraries only.

// crt_crtsetdebugfillthreshold.cpp
// compile with: /MTd
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <crtdbg.h>

void Clear( char buff[], size_t size )
{
   for( int i=0; i<size; ++i )
      buff[i] = 0;
}

void Print( char buff[], size_t size )
{
   for( int i=0; i<size; ++i )
      printf( "%02x  %c\n", (unsigned char)buff[i], buff[i] );
}

int main( void )
{
   char buff[10];

   printf( "With buffer-filling on:\n" );
   strcpy_s( buff, _countof(buff), "howdy" );
   Print( buff, _countof(buff) );

   _CrtSetDebugFillThreshold( 0 );

   printf( "With buffer-filling off:\n" );
   Clear( buff, _countof(buff) );
   strcpy_s( buff, _countof(buff), "howdy" );
   Print( buff, _countof(buff) );
}
With buffer-filling on:
68  h
6f  o
77  w
64  d
79  y
00
fd  ²
fd  ²
fd  ²
fd  ²
With buffer-filling off:
68  h
6f  o
77  w
64  d
79  y
00
00
00
00
00

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

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