strcpy, strcpy_s – cppreference.com

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From cppreference.com

Defined in header <string.h>

(1)

char

*

strcpy

(

char

*

dest,

const

char

*

src

)

;

(until C99)

char

*

strcpy

(

char

*

restrict

dest,

const

char

*

restrict

src

)

;

(since C99)

errno_t strcpy_s

(

char

*

restrict

dest, rsize_t destsz,

const

char

*

restrict

src

)

;

(2)

(since C11)

1)

Copies the null-terminated byte string pointed to by src, including the null terminator, to the character array whose first element is pointed to by dest.

The behavior is undefined if the dest array is not large enough. The behavior is undefined if the strings overlap. The behavior is undefined if either dest is not a pointer to a character array or src is not a pointer to a null-terminated byte string.

2)

Same as

(1)

, except that it may clobber the rest of the destination array with unspecified values and that the following errors are detected at runtime and call the currently installed

  • src or dest is a null pointer
  • destsz is zero or greater than

    RSIZE_MAX

  • destsz is less or equal

    strnlen_s

    (

    src, destsz

    )

    ; in other words, truncation would occur

  • overlap would occur between the source and the destination strings

Same as, except that it may clobber the rest of the destination array with unspecified values and that the following errors are detected at runtime and call the currently installed constraint handler function:

The behavior is undefined if the size of the character array pointed to by dest <=

strnlen_s

(

src, destsz

)

< destsz; in other words, an erroneous value of destsz does not expose the impending buffer overflow.

As with all bounds-checked functions, strcpy_s is only guaranteed to be available if

__STDC_LIB_EXT1__

is defined by the implementation and if the user defines

__STDC_WANT_LIB_EXT1__

to the integer constant

1

before including <string.h>.

The behavior is undefined if the size of the character array pointed to by<=; in other words, an erroneous value ofdoes not expose the impending buffer overflow.

edit]

Parameters

dest

–

pointer to the character array to write to

src

–

pointer to the null-terminated byte string to copy from

destsz

–

maximum number of characters to write, typically the size of the destination buffer

edit]

Return value

1)

returns a copy of dest

2)

returns zero on success, returns non-zero on error. Also, on error, writes zero to

dest

[

0

]

(unless dest is a null pointer or destsz is zero or greater than

RSIZE_MAX

).

edit]

Notes

strcpy_s is allowed to clobber the destination array from the last character written up to destsz in order to improve efficiency: it may copy in multibyte blocks and then check for null bytes.

The function strcpy_s is similar to the BSD function strlcpy, except that

  • strlcpy truncates the source string to fit in the destination (which is a security risk)
  • strlcpy does not perform all the runtime checks that strcpy_s does
  • strlcpy does not make failures obvious by setting the destination to a null string or calling a handler if the call fails.

Although strcpy_s prohibits truncation due to potential security risks, it’s possible to truncate a string using bounds-checked strncpy_s instead.

edit]

Example

Run this code

#define __STDC_WANT_LIB_EXT1__ 1


#include <string.h>


#include <stdio.h>


#include <stdlib.h>

 

int
 main
(
void
)


{

    
char
 
*
src 
=
 
"Take the test."
;


//  src[0] = 'M' ; // this would be undefined behavior

    
char
 dst
[
strlen
(
src
)
 
+
 
1
]
;
 
// +1 to accomodate for the null terminator

    strcpy
(
dst, src
)
;

    dst
[
0
]
 
=
 
'M'
;
 
// OK

    
printf
(
"src = %s
\n
dst = %s
\n
", src, dst
)
;

 

#ifdef __STDC_LIB_EXT1__

    set_constraint_handler_s
(
ignore_handler_s
)
;

    
int
 r 
=
 strcpy_s
(
dst, 
sizeof
 dst, src
)
;

    
printf
(
"dst = 
\"
%s
\"
, r = %d
\n
", dst, r
)
;

    r 
=
 strcpy_s
(
dst, 
sizeof
 dst, 
"Take even more tests."
)
;

    
printf
(
"dst = 
\"
%s
\"
, r = %d
\n
", dst, r
)
;


#endif


}

Possible output: 

src = Take the test.
dst = Make the test.
dst = "Take the test.", r = 0
dst = "", r = 22

edit]

References

  • C17 standard (ISO/IEC 9899:2018):
  • 7.24.2.3 The strcpy function (p: 264-265)
  • K.3.7.1.3 The strcpy_s function (p: 447)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.24.2.3 The strcpy function (p: 363)
  • K.3.7.1.3 The strcpy_s function (p: 615-616)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.21.2.3 The strcpy function (p: 326)
  • C89/C90 standard (ISO/IEC 9899:1990):
  • 4.11.2.3 The strcpy function

edit]

See also

strncpy

strncpy_s

(C11)

copies a certain amount of characters from one string to another

(function)

memcpy

memcpy_s

(C11)

copies one buffer to another

(function)

wcscpy

wcscpy_s

(C95)

(C11)

copies one wide string to another

(function)

strdup

(dynamic memory TR)

allocate a copy of a string

(function)

C++ documentation

strcpy

for

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