memcpy 와 strncpy의 차이점은 무언가요??

조금 차이점은 있죠 -_-

strcpy는 널 검사를 하기때문에
좀 느리고

memcpy는 메모리크기를 받아 그거대로 바로 복사하기때문에
더 빠르다는거......

memcpy

void *
memcpy(dst0, src0, length)
	void *dst0;
	const void *src0;
	size_t length;
{
	char *dst = dst0;
	const char *src = src0;
	size_t t;
	unsigned long u;

	_DIAGASSERT(dst0 != 0);
	_DIAGASSERT(src0 != 0);

	if (length == 0 || dst == src)		/* nothing to do */
		goto done;

	/*
	 * Macros: loop-t-times; and loop-t-times, t>0
	 */
#define	TLOOP(s) if (t) TLOOP1(s)
#define	TLOOP1(s) do { s; } while (--t)

	if ((unsigned long)dst < (unsigned long)src) {
		/*
		 * Copy forward.
		 */
		u = (unsigned long)src;	/* only need low bits */
		if ((u | (unsigned long)dst) & wmask) {
			/*
			 * Try to align operands.  This cannot be done
			 * unless the low bits match.
			 */
			if ((u ^ (unsigned long)dst) & wmask || length < wsize)
				t = length;
			else
				t = wsize - (size_t)(u & wmask);
			length -= t;
			TLOOP1(*dst++ = *src++);
		}
		/*
		 * Copy whole words, then mop up any trailing bytes.
		 */
		t = length / wsize;
		TLOOP(*(word *)(void *)dst = *(const word *)(const void *)src; src += wsize; dst += wsize);
		t = length & wmask;
		TLOOP(*dst++ = *src++);
	} else {
		/*
		 * Copy backwards.  Otherwise essentially the same.
		 * Alignment works as before, except that it takes
		 * (t&wmask) bytes to align, not wsize-(t&wmask).
		 */
		src += length;
		dst += length;
		u = (unsigned long)src;
		if ((u | (unsigned long)dst) & wmask) {
			if ((u ^ (unsigned long)dst) & wmask || length <= wsize)
				t = length;
			else
				t = (size_t)(u & wmask);
			length -= t;
			TLOOP1(*--dst = *--src);
		}
		t = length / wsize;
		TLOOP(src -= wsize; dst -= wsize; *(word *)(void *)dst = *(const word *)(const void *)src);
		t = length & wmask;
		TLOOP(*--dst = *--src);
	}
done:
	return (dst0);
}

strncpy

char *
strncpy(dst, src, n)
	char *dst;
	const char *src;
	size_t n;
{

	_DIAGASSERT(dst != NULL);
	_DIAGASSERT(src != NULL);

	if (n != 0) {
		char *d = dst;
		const char *s = src;

		do {
			if ((*d++ = *s++) == 0) {
				/* NUL pad the remaining n-1 bytes */
				while (--n != 0)
					*d++ = 0;
				break;
			}
		} while (--n != 0);
	}
	return (dst);
}

From BSD.

만들기 나름입니다.

7.21.2.4 The strncpy function
    Synopsis
1        #include <string.h>
          char *strncpy(char * restrict s1, const char * restrict s2, size_t n);

    Description
2        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 by s1. If copying takes place between objects
          that overlap, the behavior is undefined. 3 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.

PS. 생각해 보니 카피하고 나서 체크후 지워도 될 꺼 같다는 생각도 드는군요;
음.. 저 괄호속 문장이 src와 dst를 결과적으로 비교할 때 성립해야 한다는 건지,
아니면 카피하는 행위 자체를 하지 말라는 건지 헷갈리네요. 어느 경우에건 한번
이상의 null character 체크는 해야 하겠지만요.