c - Difference between strncpy and memcpy?

Question

How can i access s[7] in s?

I didn't observe any difference between strncpy and memcpy. If I want to print the output s, along with s[7] (like qwertyA), what are the changes I have to made in the following code:

#include <stdio.h>
#include <stdlib.h>
int main()
{
    char s[10] = "qwerty", str[10], str1[10];
    s[7] = 'A';
    printf("%s
",s);
    strncpy(str,s,8);
    printf("%s
",str);
    memcpy(str1,s,8);
    printf("%s
",str1);
    return 0;
}
/*
O/P
qwerty
qwerty
qwerty
*/

Answer 1

Others have pointed out your null-termination problems. You need to understand null-termination before you understand the difference between memcpy and strncpy.

The main difference is that memcpy will copy all N characters you ask for, while strncpy will copy up to the first null terminator inclusive, or N characters, whichever is fewer.

In the event that it copies less than N characters, it will pad the rest out with null characters.