man pages section 3: Basic Library Functions

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Updated: July 2014
 
 

memccpy(3C)

Name

memory, memccpy, memchr, memcmp, memcpy, memmove, memset, memmem - memory operations

Synopsis

#include <string.h>

void *memccpy(void *restrict s1, const void *restrict s2,
     int c, size_t n);
void *memchr(const void *s, int c, size_t n);
int memcmp(const void *s1, const void *s2, size_t n);
void *memcpy(void *restrict s1, const void *restrict s2, size_t n);
void *memmove(void *s1, const void *s2, size_t n);
void *memset(void *s, int c, size_t n);
void *memmem(const void *haystack, size_t haystacklen, const void *needle,
     size_t needlelen);

ISO C++

#include <string.h>

const void *memchr(const void *s, int c, size_t n);
#include <cstring>

void *std::memchr(void *s, int c, size_t n);

Description

These functions operate as efficiently as possible on memory areas (arrays of bytes bounded by a count, not terminated by a null character). They do not check for the overflow of any receiving memory area.

The memccpy() function copies bytes from memory area s2 into s1, stopping after the first occurrence of c (converted to an unsigned char) has been copied, or after n bytes have been copied, whichever comes first. It returns a pointer to the byte after the copy of c in s1, or a null pointer if c was not found in the first n bytes of s2.

The memchr() function returns a pointer to the first occurrence of c (converted to an unsigned char) in the first n bytes (each interpreted as an unsigned char) of memory area s, or a null pointer if c does not occur.

The memcmp() function compares its arguments, looking at the first n bytes (each interpreted as an unsigned char), and returns an integer less than, equal to, or greater than 0, according as s1 is lexicographically less than, equal to, or greater than s2 when taken to be unsigned characters.

The memcpy() function copies n bytes from memory area s2 to s1. It returns s1. If copying takes place between objects that overlap, the behavior is undefined.

The memmove() function copies n bytes from memory area s2 to memory area s1. Copying between objects that overlap will take place correctly. It returns s1.

The memset() function sets the first n bytes in memory area s to the value of c (converted to an unsigned char). It returns s.

The memmem() function locates the start of the first occurrence of the substring needle of length needlelen in the memory area haystack of length haystacklen. It returns a pointer to the start of the substring, or NULL if the substring is not found.

Usage

Using memcpy() might be faster than using memmove() if the application knows that the objects being copied do not overlap.

Attributes

See attributes(5) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
MT-Safe
Standard

See Also

string(3C), attributes(5), standards(5)

Notes

Overlap between objects being copied can arise even when their (virtual) address ranges appear to be disjoint; for example, as a result of memory-mapping overlapping portions of the same underlying file, or of attaching the same shared memory segment more than once.