strncpy,strcpy,memcpy的区别

strcpy和memcpy都是标准C库函数，它们有下面的特点：
strcpy提供了字符串的复制。即strcpy只用于字符串复制，并且它不仅复制字符串内容之外，还会复制字符串的结束符。

已知strcpy函数的原型是：char* strcpy(char* dest, const char* src);
memcpy提供了一般内存的复制。即memcpy对于需要复制的内容没有限制，因此用途更广。
void *memcpy( void *dest, const void *src, size_t count );

char *strcpy(char * dest, const char * src) // 实现src到dest的复制

{

　　if ((src == NULL) || (dest == NULL)) //判断参数src和dest的有效性

　　{

 

　　　　　　return NULL;

　　}

　　char *strdest = dest;        //保存目标字符串的首地址

　　while ((*strDest++ = *strSrc++)!='\0');//把src字符串的内容复制到dest下

　　return strdest;

}

void *memcpy(void *memTo,const void *memFrom,size_t size)

{

　　if((memTo == NULL) || (memFrom == NULL)) //memTo和memFrom必须有效

         return NULL;

　　char *tempFrom = (char *)memFrom;            //保存memFrom首地址

　　char *tempTo = (char *)memTo;                 //保存memTo首地址     

　　while(size -- > 0)                //循环size次，复制memFrom的值到memTo中

       　　*tempTo++ = *tempFrom++ ; 

　　return memTo;

}

strcpy和memcpy主要有以下3方面的区别。
1、复制的内容不同。strcpy只能复制字符串，而memcpy可以复制任意内容，例如字符数组、整型、结构体、类等。
2、复制的方法不同。strcpy不需要指定长度，它遇到被复制字符的串结束符"\0"才结束，所以容易溢出。memcpy则是根据其第3个参数决定复制的长度。
3、用途不同。通常在复制字符串时用strcpy，而需要复制其他类型数据时则一般用memcpy

memcpy

Summary

#include <string.h>void *memcpy (  void *dest,   /* destination buffer */  void *src,    /* source buffer */  int len);     /* bytes to copy */

Description

The memcpy function copies len bytes from src to dest. If these memory buffers overlap, the memcpy function cannot guarantee that bytes insrc are copied to dest before being overwritten. If these buffers do overlap, use the memmove function.

Return Value

The memcpy function returns dest.

See Also

memccpy, memchr, memcmp,memmove, memset

Example

#include <string.h>#include <stdio.h> /* for printf */void tst_memcpy (void) {  char src1 [100] = "Copy this string to dst1";  char dst1 [100];  char *p;  p = memcpy (dst1, src1, sizeof (dst1));  printf ("dst = \"%s\"\n", p);}

strcpy

Summary

#include <string.h>char *strcpy (  char *dst,    /* destination string */  char *src);   /* source string */

Description

The strcpy function copies characters from src to dst up to and including the terminating null character.

Return Value

The strcpy function returns dst.

See Also

strcat, strlen, strncat,strncpy

Example

#include <string.h>#include <stdio.h> /* for printf */void tst_strcpy (void) {  char buf [21];  char s [] = "Test String";  strcpy (buf, s);  strcat (buf, " #2");  printf ("new string is %s\n", buf);}

strncpy

Summary

#include <string.h>char *strncpy (  char *dst,   /* destination string */  char *src,   /* source string */  int len);    /* max characters to copy */

Description

The strncpy function copies at most len characters from src todst. Characters are copied until a null character ('\0') is copied or untillen characters have been copied. If the length ofsrc is less than len the remaining bytes in dst are padded with null characters ('\0').

Return Value

The strncpy function returns dst.

See Also

strcat, strcpy, strlen,strncat

Example

#include <string.h>#include <stdio.h> /* for printf */void tst_strncpy (char *s) {  char buf [21];  strncpy (buf, s, sizeof (buf));  buf [sizeof (buf) -1] = '\0';}