_CrtSetDebugFillThreshold

 

For the latest documentation on Visual Studio 2017, see Visual Studio 2017 Documentation.

For the latest documentation on Visual Studio 2017, see _CrtSetDebugFillThreshold on docs.microsoft.com. Retrieves or modifies the threshold controlling buffer-filling behavior in debug functions.

size_t _CrtSetDebugFillThreshold(  
   size_t _NewThreshold  
);  

Parameters

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.

RoutineRequired header
_CrtSetDebugFillThreshold<crtdbg.h>

For more compatibility information, see Compatibility in the Introduction.

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.

Debug Routines

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