strncpy

 

C

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Strings library

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Null-terminated byte strings

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Defined in header <string.h>
char *strncpy( char          *dest, const char          *src, size_t count );		(until C99)
char *strncpy( char *restrict dest, const char *restrict src, size_t count );		(since C99)

Copies at most count characters of the byte string pointed to by src (including the terminating null character) to character array pointed to by dest.

If count is reached before the entire string src was copied, the resulting character array is not null-terminated.

If, after copying the terminating null character from src, count is not reached, additional null characters are written to dest until the total of count characters have been written.

If the strings overlap, the behavior is undefined.

Parameters

dest	-	pointer to the character array to copy to
src	-	pointer to the byte string to copy from
count	-	maximum number of characters to copy

Return value

dest

Example

Run this code

#include <stdio.h>
#include <string.h>
 
int main(void)
{
    char str[] = "Hello, world!";
    char copy[40] = { 0 };
 
    /* no buffer overflow */
    strncpy(copy, str, sizeof(copy)-1);
    printf("%s\n", copy);
 
    /* copy partial amount of data */
    strncpy(copy, str, 5);
 
    /* add manually nullbyte.
     * comment it to see difference */
    copy[5] = '\0';
    printf("%s\n", copy);
 
    return 0;
}

Output:

Hello, world!
Hello

See also

strcpy	copies one string to another (function)
memcpy	copies one buffer to another (function)
C++ documentation for strncpy