_dupenv_s_dbg, _wdupenv_s_dbg

發行項
01/04/2008

Get a value from the current environment. Versions of _dupenv_s, _wdupenv_s that allocate memory with _malloc_dbg to provide additional debugging information.

errno_t _dupenv_s_dbg(
   char **buffer,
   size_t *numberOfElements,
   const char *varname,
   int blockType,
   const char *filename,
   int linenumber
);
errno_t _wdupenv_s_dbg(
   wchar_t **buffer,
   size_t * numberOfElements,
   const wchar_t *varname,
   int blockType,
   const char *filename,
   int linenumber
);

Parameters

buffer
Buffer to store the variable's value.
numberOfElements
Size of buffer.
varname
Environment variable name.
blockType
Requested type of the memory block: _CLIENT_BLOCK or _NORMAL_BLOCK.
filename
Pointer to the name of the source file or NULL.
linenumber
Line number in source file or NULL.

Return Value

Zero on success, an error code on failure.

These functions validate their parameters; if buffer or varname is NULL, the invalid parameter handler is invoked as described in Parameter Validation. If execution is allowed to continue, the functions set errno to EINVAL and return EINVAL.

If these functions cannot allocate enough memory, they set buffer to NULL and numberOfElements to 0, and return ENOMEM.

Remarks

The _dupenv_s_dbg and _wdupenv_s_dbg functions are identical to _dupenv_s and _wdupenv_s except that, when _DEBUG is defined, these functions use the debug version of malloc, _malloc_dbg, to allocate memory for the value of the environment variable. For information on the debugging features of _malloc_dbg, see _malloc_dbg.

You do not need to call these functions explicitly in most cases. Instead, you can define the flag _CRTDBG_MAP_ALLOC. When _CRTDBG_MAP_ALLOC is defined, calls to _dupenv_s and _wdupenv_s are remapped to _dupenv_s_dbg and _wdupenv_s_dbg, respectively, with the blockType set to _NORMAL_BLOCK. Thus, you do not need to call these functions explicitly unless you want to mark the heap blocks as _CLIENT_BLOCK. For more information on block types, see Types of Blocks on the Debug Heap.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
_tdupenv_s_dbg	_dupenv_s_dbg	_dupenv_s_dbg	_wdupenv_s_dbg

Requirements

Routine	Required header
_dupenv_s_dbg	<crtdbg.h>
_wdupenv_s_dbg	<crtdbg.h>

For additional compatibility information, see Compatibility in the Introduction.

Example

// crt_dupenv_s_dbg.c
#include  <stdlib.h>
#include <crtdbg.h>

int main( void )
{
   char *pValue;
   size_t len;
   errno_t err = _dupenv_s_dbg( &pValue, &len, "pathext",
      _NORMAL_BLOCK, __FILE__, __LINE__ );
   if ( err ) return -1;
   printf( "pathext = %s\n", pValue );
   free( pValue );
   err = _dupenv_s_dbg( &pValue, &len, "nonexistentvariable",
      _NORMAL_BLOCK, __FILE__, __LINE__ );
   if ( err ) return -1;
   printf( "nonexistentvariable = %s\n", pValue );
   free( pValue ); // It's OK to call free with NULL
}

Sample Output

pathext = .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.pl
nonexistentvariable = (null)

.NET Framework Equivalent

System::Environment::GetEnvironmentVariable

共用方式為