Difference between revisions of "c/string/byte/strcpy"
From cppreference.com
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:* {{tt|destsz}} is less or equal {{c|strnlen_s(src, destsz)}}; in other words, truncation would occur | :* {{tt|destsz}} is less or equal {{c|strnlen_s(src, destsz)}}; in other words, truncation would occur | ||
:* overlap would occur between the source and the destination strings | :* overlap would occur between the source and the destination strings | ||
| − | @@The behavior is undefined if the size of the character array pointed to by dest <= {{c|strnlen_s(src, destsz)}} < {{ | + | @@The behavior is undefined if the size of the character array pointed to by {{tt|dest}} <= {{c|strnlen_s(src, destsz)}} < {{tt|destsz}}; in other words, an erroneous value of {{tt|destsz}} does not expose the impending buffer overflow. |
:As all bounds-checked functions, {{tt|strcpy_s}} is only guaranteed to be available if {{c|__STDC_LIB_EXT1__}} is defined by the implementation and if the user defines {{c|__STDC_WANT_LIB_EXT1__}} to the integer constant {{c|1}} before including {{tt|string.h}}. | :As all bounds-checked functions, {{tt|strcpy_s}} is only guaranteed to be available if {{c|__STDC_LIB_EXT1__}} is defined by the implementation and if the user defines {{c|__STDC_WANT_LIB_EXT1__}} to the integer constant {{c|1}} before including {{tt|string.h}}. | ||
Revision as of 03:50, 16 September 2015
| 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 constraint handler function:
-
srcordestis a null pointer -
destszis zero or greater than RSIZE_MAX -
destszis less or equal strnlen_s(src, destsz); in other words, truncation would occur - overlap would occur between the source and the destination strings
-
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 all bounds-checked functions,
strcpy_sis 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 includingstring.h.
Contents |
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 |
Return value
1) returns a copy of
dest2) 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).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
-
strlcpytruncates the source string to fit in the destination (which is a security risk) -
strlcpydoes not perform all the runtime checks thatstrcpy_sdoes -
strlcpydoes 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.
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\ndst = %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
References
- 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
See also
| (C11) |
copies a certain amount of characters from one string to another (function) |
| (C11) |
copies one buffer to another (function) |
| (C95)(C11) |
copies one wide string to another (function) |
| C++ documentation for strcpy
| |
