strncpy.c

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/***************************************************************************//**
 @file strncpy.c
 
 @brief Defines the strncpy function
*******************************************************************************/
#include <string.h>
 
/*******************************************************************************
 strncpy
*//**
 @brief Copies no more than n characters with null terminator from s2 to s1
 @param *s1 The destination array
 @param *s2 The source string
 @param n Maximum number of characters to copy
 
 The strncpy function copies not more than n characters (characters that
 follow a null character are not copied) from the array pointed to by s2 to
 the array pointed to be s1. If the array pointed to by s2 is a string that
 is shorter than n characters, null characters are appended to the copy in
 the array pointed to by s1, until n characters in all have been written.
 
 @note Copying between overlapping objects is supported, but the source may
 be overwritten.
 
 @return The value of s1
*******************************************************************************/
char *
strncpy(char *s1, const char *s2, size_t n)
{
 size_t len = strlen(s2);
 
 if ( !s1 ||
 !s2 ||
 /* Check for wrapping while copying */
 ((((unsigned long) -1) - ((unsigned long) s1)) < len) ||
 ((((unsigned long) -1) - ((unsigned long) s2)) < len))
 {
 return s1;
 }
 
 if (n <= len)
 {
 /* Copy partial string contents with no NUL */
 memmove(s1, s2, n);
 }
 else
 {
 /* Copy the entire string and NUL out the remaining bytes */
 strcpy(s1, s2);
 memset(s1 + len + 1, '\0', n - len - 1);
 }
 
 return s1;
}