C library function -memset()

C Standard Library - <string.h>

Description

C Library Functionsvoid *memset(void *str, int c, size_t n)Used to set a block of memory to a specified value.

The memset() function copies the specified value c to the first n bytes of the memory area pointed to by str, which can be used to clear a memory block or set it to a specific value.

In some cases, when it is necessary to quickly initialize a large block of memory to zero or a specific value, memset() can provide an efficient implementation.

When clearing a memory area or assigning a value to a memory area, memset() is a commonly used utility function.

Declaration

void *memset(void *ptr, int value, size_t num);

The following is the declaration of the memset() function.

void *memset(void *str, int c, size_t n)

Parameter

  • str-- A pointer to the memory area to be filled.
  • c-- The value to be set, usually an unsigned character.
  • n-- The number of bytes to be set to that value.

Return Value

This function returns a pointer to the memory area str.

Notes

  • memset()not on pointersptrNo boundary checks are performed on the pointed-to memory area; therefore, when using it, ensureptrthat the pointed-to memory area is large enough to avoid out-of-bounds access.
  • memset()the second parametervalueusually aintA value of type, but actually only the low 8 bits of the value are used. This means in the range0to255values outside this range may produce undefined behavior.
  • numThe parameter indicates the number of bytes to be set, usually viasizeof()or obtained by other means.

Example

The following example demonstrates the usage of the memset() function.

Example

#include <stdio.h> #include <string.h> int main () { char str[50]; strcpy(str,"This is string.h library function"); puts(str); memset(str,'$',7); puts(str); return(0); }

Let us compile and run the above program, which will produce the following result:

This is string.h library function
$$$$$$$ string.h library function

Example

#include <stdio.h>
#include <string.h> // Include the string.h header file to use memset

int main() {
    char buffer[10];

    // Set the first 5 bytes of the buffer array to the character 'A', and add a string terminator
    memset(buffer, 'A', 5);
    buffer[5] = '\0'; // Make sure to add the string terminator
    printf("Buffer after memset: %s\n", buffer);

    // Clear the buffer array to zero, using '\0' instead of 0.
    memset(buffer, '\0', sizeof(buffer)); // Use '\0' for consistency and readability
    printf("Buffer after memset: %s\n", buffer);

    return 0;
}

Let us compile and run the above program, which will produce the following result:

Buffer after memset: AAAAA
Buffer after memset:

C Standard Library - <string.h>

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