_CrtSetDebugFillThreshold

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

size_t _CrtSetDebugFillThreshold(
   size_t _NewThreshold
);

Parameters

• newThreshold
  New threshold.

Return Value

The previous threshold.

Remarks

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.

• strcpy_s, wcscpy_s, _mbscpy_s

• strncpy_s, _strncpy_s_l, wcsncpy_s, _wcsncpy_s_l, _mbsncpy_s, _mbsncpy_s_l

• _mbsnbcpy_s, _mbsnbcpy_s_l

• strcat_s, wcscat_s, _mbscat_s

• strncat_s, _strncat_s_l, wcsncat_s, _wcsncat_s_l, _mbsncat_s, _mbsncat_s_l

• _mbsnbcat_s, _mbsnbcat_s_l

• _strset_s, _strset_s_l, _wcsset_s, _wcsset_s_l, _mbsset_s, _mbsset_s_l

• _strnset_s, _strnset_s_l, _wcsnset_s, _wcsnset_s_l, _mbsnset_s, _mbsnset_s_l

• _mbsnbset_s, _mbsnbset_s_l

• _makepath_s, _wmakepath_s

• _splitpath_s, _wsplitpath_s

• _strlwr_s, _strlwr_s_l, _mbslwr_s, _mbslwr_s_l, _wcslwr_s, _wcslwr_s_l

• _strupr_s, _strupr_s_l, _mbsupr_s, _mbsupr_s_l, _wcsupr_s, _wcsupr_s_l

• strerror_s, _strerror_s, _wcserror_s, __wcserror_s

• _itoa_s, _i64toa_s, _ui64toa_s, _itow_s, _i64tow_s, _ui64tow_s

• _ecvt_s

• _fcvt_s

• _gcvt_s

Requirements

For more compatibility information, see Compatibility in the Introduction.

Libraries

Debug versions of C run-time libraries only.

Example

// 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

.NET Framework Equivalent

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

See Also

Concepts

Debug Routines