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memcpy(3c)
Standard C Library Functions memory(3C)
NAME
memory, memccpy, memchr, memcmp, memcpy, memmove, memset, explicit_mem‐
set, memmem - memory operations
memcpy_s, memmove_s, memset_s - memory operations with additional
safety checks
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 *explicit_memset(void *s, int c, size_t n);
void *memmem(const void *haystack, size_t haystacklen,
const void *needle, size_t needlelen);
#define __STDC_WANT_LIB_EXT1__ 1
#include <string.h>
errno_t memcpy_s(void *restrict s1, rsize_t s1max,
const void *restrict s2, rsize_t n);
errno_t memmove_s(void *s1, rsize_t s1max,
const void *s2, rsize_t n);
errno_t memset_s(void *s, rsize_t smax, int c, rsize_t n);
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 charac‐
ter). They do not check for the overflow of any receiving memory area.
The memccpy() function copies bytes from memory area s2 into s1, stop‐
ping 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 lexicograph‐
ically 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 cor‐
rectly. 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 explicit_memset() function performs the same operation as memset().
It differs from memset() in that it will not be removed by compiler
dead store analysis. The explicit_memset() function is useful for
clearing no longer needed sensitive data to ensure that it does not
remain accessible in process memory.
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. If needlelen is zero, haystack
is returned. If haystacklen is less than needlelen, NULL is returned.
The memcpy_s(), memmove_s(), and memset_s() functions are part of the
C11 bounds checking interfaces specified in the C11 standard, Annex K.
Each provide equivalent functionality to the respective memcpy(), mem‐
move(), and memset() functions, except with differing parameters and
return type in order to provide explicit runtime-constraints as defined
in the C11 standard. See runtime_constraint_handler(3C) and
INCITS/ISO/IEC 9899:2011.
RETURN VALUES
If no runtime-constraint violation is detected, the memcpy_s(), mem‐
move_s(), and memset_s() functions return zero. Otherwise they return a
non-zero value.
ERRORS
The memcpy_s() function will fail if:
EINVAL NULL pointer passed or source and destination overlap.
ERANGE size argument is invalid, that is, s1max or n is greater than
RSIZE_MAX or n is greater than s1max.
The memmove_s() function will fail if:
EINVAL NULL pointer passed.
ERANGE size argument is invalid, that is, s1max or n is greater than
RSIZE_MAX or n is greater than s1max.
The memset_s() function will fail if:
EINVAL NULL pointer passed.
ERANGE size argument is invalid, that is, smax or n is greater than
RSIZE_MAX or n is greater than smax.
USAGE
Using memcpy() might be faster than using memmove() if the application
knows that the objects being copied do not overlap.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSee below _
StandardSee standards(7).
The memcpy(), memccpy(), memchr(), memcmp(), memcpy(), memmove(), mem‐
set(), explicit_memset(), and memmem() functions can be used safely in
multithreaded applications.
The memcpy_s(), memmove_s(), and memset_s() functions cannot be used
safely in a multithreaded application due to the runtime constraint
handler. For more information, see the runtime_constraint_handler(3C)
man page.
SEE ALSO
timingsafe_memcmp(3C), string(3C), attributes(7), standards(7), run‐
time_constraint_handler(3C)
NOTES
Overlap between objects being copied can arise even when their (vir‐
tual) 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.
Oracle Solaris 11.4 3 July 2020 memory(3C)