strncpy.c

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#include <string.h>
 
char* strncpy(char* _RESTRICT s1, const char* _RESTRICT s2, size_t n)
{
    char* rc = s1;
 
    while (n && (*s1++ = *s2++))
    {
        /* Cannot do "n--" in the conditional as size_t is unsigned and we have
           to check it again for >0 in the next loop below, so we must not risk
           underflow.
        */
        --n;
    }
 
    /* Checking against 1 as we missed the last --n in the loop above. */
    while (n-- > 1)
    {
        *s1++ = '\0';
    }
 
    return rc;
}