memcpy, memcpy_s

 

C

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headers

Type support

Dynamic memory management

Error handling

Program utilities

Variadic function support

Date and time utilities

Strings library

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Numerics

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Thread support (C11)

Atomic operations (C11)

Technical Specifications

 

Strings library

Byte strings

Multibyte strings

Wide strings

 

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to numeric formats
atof atoiatolatoll strtolstrtoll	strtoulstrtoull strtofstrtodstrtold strtoimaxstrtoumax (C99)(C99)
String manipulation
strcpystrcpy_s (C11)
strncpystrncpy_s (C11)
strcatstrcat_s (C11)
strncatstrncat_s (C11)
strxfrm
String examination
strlenstrnlen_s (C11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (C11)
Memory manipulation
memchr
memcmp
memsetmemset_s (C11)
memcpymemcpy_s (C11)
memmovememmove_s (C11)
Miscellaneous
strerrorstrerror_sstrerrorlen_s (C11)(C11)

 

Defined in header <string.h>
	(1)
void* memcpy( void *dest, const void *src, size_t count );			(until C99)
void* memcpy( void *restrict dest, const void *restrict src, size_t count );			(since C99)
errno_t memcpy_s( void *restrict dest, rsize_t destsz,                   const void *restrict src, rsize_t count );		(2)	(since C11)

1) Copies count characters from the object pointed to by src to the object pointed to by dest. Both objects are interpreted as arrays of unsigned char.

The behavior is undefined if access occurs beyond the end of the dest array. If the objects overlap (which is a violation of the restrict contract) (since C99), the behavior is undefined. The behavior is undefined if either dest or src is a null pointer.

2) Same as (1), except that the following errors are detected at runtime and cause the entire destination range [dest, dest+destsz) to be zeroed out (if both dest and destsz are valid), as well as call the currently installed constraint handler function:

• dest or src is a null pointer
• destsz or count is greater than RSIZE_MAX
• count is greater than destsz (buffer overflow would occur)
• the source and the destination objects overlap

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

As all bounds-checked functions, memcpy_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.

Parameters

dest	-	pointer to the object to copy to
destsz	-	max number of bytes to modify in the destination (typically the size of the destination object)
src	-	pointer to the object to copy from
count	-	number of bytes to copy

Return value

1) Returns a copy of dest

2) Returns zero on success and non-zero value on error. Also on error, if dest is not a null pointer and destsz is valid, writes destsz zero bytes in to the destination array.

Notes

memcpy may be used to set the effective type of an object obtained by an allocation function.

memcpy is the fastest library routine for memory-to-memory copy. It is usually more efficient than strcpy, which must scan the data it copies or memmove, which must take precautions to handle overlapping inputs.

Several C compilers transform suitable memory-copying loops to memcpy calls.

Where strict aliasing prohibits examining the same memory as values of two different types, memcpy may be used to convert the values.