strcpy_s, wcscpy_s, _mbscpy_s

Article
06/05/2017

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The latest version of this topic can be found at strcpy_s, wcscpy_s, _mbscpy_s.

Copies a string. These versions of strcpy, wcscpy, _mbscpy have security enhancements, as described in Security Features in the CRT.

Important

_mbscpy_s cannot be used in applications that execute in the Windows Runtime. For more information, see CRT functions not supported with /ZW.

Syntax

errno_t strcpy_s(  
   char *strDestination,  
   size_t numberOfElements,  
   const char *strSource   
);  
errno_t wcscpy_s(  
   wchar_t *strDestination,  
   size_t numberOfElements,  
   const wchar_t *strSource   
);  
errno_t _mbscpy_s(  
   unsigned char *strDestination,  
   size_t numberOfElements,  
   const unsigned char *strSource   
);  
template <size_t size>  
errno_t strcpy_s(  
   char (&strDestination)[size],  
   const char *strSource   
); // C++ only  
template <size_t size>  
errno_t wcscpy_s(  
   wchar_t (&strDestination)[size],  
   const wchar_t *strSource   
); // C++ only  
template <size_t size>  
errno_t _mbscpy_s(  
   unsigned char (&strDestination)[size],  
   const unsigned char *strSource   
); // C++ only

Parameters

strDestination
Location of the destination string buffer.

numberOfElements
Size of the destination string buffer in char units for narrow and multi-byte functions, and wchar_t units for wide functions.

strSource
Null-terminated source string buffer.

Return Value

Zero if successful; otherwise, an error.

Error Conditions

`strDestination`	`numberOfElements`	`strSource`	Return value	Contents of `strDestination`
`NULL`	any	any	`EINVAL`	not modified
any	any	`NULL`	`EINVAL`	`strDestination`[0] set to 0
any	0, or too small	any	`ERANGE`	`strDestination`[0] set to 0

Remarks

The strcpy_s function copies the contents in the address of strSource, including the terminating null character, to the location that's specified by strDestination. The destination string must be large enough to hold the source string and its terminating null character. The behavior of strcpy_s is undefined if the source and destination strings overlap.

wcscpy_s is the wide-character version of strcpy_s, and _mbscpy_s is the multibyte-character version. The arguments and return value of wcscpy_s are wide-character strings; those of _mbscpy_s are multibyte-character strings. These three functions behave identically otherwise.

If strDestination or strSource is a null pointer, or if the destination string is too small, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, these functions return EINVAL and set errno to EINVAL when strDestination or strSource is a null pointer, and they return ERANGE and set errno to ERANGE when the destination string is too small.

Upon successful execution, the destination string is always null-terminated.

In C++, use of these functions is simplified by template overloads that can infer buffer length automatically so that you don't have to specify a size argument, and they can automatically replace older, less-secure functions with their newer, more secure counterparts. For more information, see Secure Template Overloads.

The debug versions of these functions first fill the buffer with 0xFE. To disable this behavior, use _CrtSetDebugFillThreshold.

Generic-Text Routine Mappings

TCHAR.H routine	_UNICODE & _MBCS not defined	_MBCS defined	_UNICODE defined
`_tcscpy_s`	`strcpy_s`	`_mbscpy_s`	`wcscpy_s`

Requirements

Routine	Required header
`strcpy_s`	<string.h>
`wcscpy_s`	<string.h> or <wchar.h>
`_mbscpy_s`	<mbstring.h>

For additional compatibility information, see Compatibility.

Example

// crt_strcpy_s.cpp  
// This program uses strcpy_s and strcat_s  
// to build a phrase.  
//  
  
#include <string.h>  
#include <stdlib.h>  
#include <stdio.h>  
#include <errno.h>  
  
int main( void )  
{  
   char string[80];  
   // using template versions of strcpy_s and strcat_s:  
   strcpy_s( string, "Hello world from " );  
   strcat_s( string, "strcpy_s " );  
   strcat_s( string, "and " );  
   // of course we can supply the size explicitly if we want to:  
   strcat_s( string, _countof(string), "strcat_s!" );  
  
   printf( "String = %s\n", string );  
}

String = Hello world from strcpy_s and strcat_s!

.NET Framework Equivalent

System::String::Copy