std::memset

 

C++

Language

Standard library headers

Concepts

Utilities library

Strings library

Containers library

Algorithms library

Iterators library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical Specifications

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

char_traits

 

Null-terminated byte strings

Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C++11)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to numeric formats
atof atoiatolatoll strtolstrtoll	strtoulstrtoull strtofstrtodstrtold strtoimaxstrtouimax (C++11)(C++11)
String manipulation
strcpy
strncpy
strcat
strncat
strxfrm
String examination
strlen strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtok
Memory manipulation
memchr
memcmp
memset
memcpy
memmove
Miscellaneous
strerror

 

Defined in header <cstring>
void* memset( void* dest, int ch, std::size_t count );

Converts the value ch to unsigned char and copies it into each of the first count characters of the object pointed to by dest. If the object is not trivially-copyable (e.g., scalar, array, or a C-compatible struct), the behavior is undefined. If count is greater than the size of the object pointed to by dest, the behavior is undefined.

Parameters

dest	-	pointer to the object to fill
ch	-	fill byte
count	-	number of bytes to fill

Return value

dest

Notes

std::memset may be optimized away (under the as-if rules) if the object modified by this function is not accessed again for the rest of its lifetime. For that reason, this function cannot be used to scrub memory (e.g. to fill an array that stored a password with zeroes).

Example

Run this code

#include <iostream>
#include <cstring>
 
int main()
{
    int a[20];
    std::memset(a, 0, sizeof a);
    for (int ai : a) std::cout << ai;
}

Output:

00000000000000000000

See also

memcpy	copies one buffer to another (function)
wmemset	copies the given wide character to every position in a wide character array (function)
fill	assigns a range of elements a certain value (function template)
fill_n	assigns a value to a number of elements (function template)
is_trivially_copyable (C++11)	checks if a type is trivially copyable (class template)
C documentation for memset