Initialize characters of a string to a given character. More secure versions of these functions exist; see _strnset_s, _strnset_s_l, _wcsnset_s, _wcsnset_s_l, _mbsnset_s, _mbsnset_s_l.
char *_strnset(
   char *str,
   int c,
   size_t count 
);
char *_strnset_l(
   char *str,
   int c,
   size_t count,
   locale_t locale
);
wchar_t *_wcsnset(
   wchar_t *str,
   wchar_t c,
   size_t count 
);
wchar_t *_wcsnset_l(
   wchar_t *str,
   wchar_t c,
   size_t count,
   _locale_t locale
);
unsigned char *_mbsnset(
   unsigned char *str,
   unsigned int c,
   size_t count 
);
unsigned char *_mbsnset_l(
   unsigned char *str,
   unsigned int c,
   size_t count,
   _locale_t locale
);
Parameters
- str 
 String to be altered.
- c 
 Character setting.
- count 
 Number of characters to be set.
- locale 
 Locale to use.
Return Value
Returns a pointer to the altered string.
Remarks
The _strnset function sets, at most, the first count characters of str to c (converted to char). If count is greater than the length of str, the length of str is used instead of count.
_wcsnset and _mbsnset are wide-character and multibyte-character versions of _strnset. The string arguments and return value of _wcsnset are wide-character strings; those of _mbsnset are multibyte-character strings. These three functions behave identically otherwise.
_mbsnset validates its parameters; if str is a null pointer, the invalid parameter handler is invoked, as described in Parameter Validation . If execution is allowed to continue, _mbsnset returns NULL and sets errno to EINVAL. _strnset and _wcsnset do not validate their parameters.
The output value is affected by the setting of the LC_CTYPE category setting of the locale; see setlocale for more information. The versions of these functions without the _l suffix use the current locale for this locale-dependent behavior; the versions with the _l suffix are identical except that they use the locale parameter passed in instead. For more information, see Locale.
Generic-Text Routine Mappings
| TCHAR.H routine | _UNICODE & _MBCS not defined | _MBCS defined | _UNICODE defined | 
|---|---|---|---|
| _tcsnset | _strnset | _mbsnbset | _wcsnset | 
| _tcsnset_l | _strnset_l | _mbsnbset_l | _wcsnset_l | 
Requirements
| Routine | Required header | 
|---|---|
| _strnset | <string.h> | 
| _strnset_l | <tchar.h> | 
| _wcsnset | <string.h> or <wchar.h> | 
| _wcsnset_l | <tchar.h> | 
| _mbsnset, _mbsnset_l | <mbstring.h> | 
For additional compatibility information, see Compatibility in the Introduction.
Example
// crt_strnset.c
// compile with: /W3
#include <string.h>
#include <stdio.h>
int main( void )
{
   char string[15] = "This is a test";
   /* Set not more than 4 characters of string to be *'s */
   printf( "Before: %s\n", string );
   _strnset( string, '*', 4 ); // C4996
   // Note: _strnset is deprecated; consider using _strnset_s
   printf( "After:  %s\n", string );
}
Before: This is a test
After:  **** is a test