用memmove函数代替strncpy函数

上一篇 / 下一篇 2012-08-29 11:02:12 / 个人分类：C++

}U[b9I5a|z0　　有过C语言编程的朋友应该都有过指针越界的困扰。不管越界的地方是全局地址、还是局部地址，查起来都是非常麻烦，原因大多时候都来自于自己对 char数组类型的误用。很多同学可能都不是很清楚，在str系类的函数中，函数会在结尾的时候添加NULL指针。比如说strncpy函数，在 linux kernel上是这样写的

F u"\^7Q5n0 51Testing软件测试网r Aa,KA\.D2h

/**
$Pxfw3S:f |xhi%o0 * strncpy - Copy a length-limited, %NUL-terminated string
_!] j0I%b$Ce0 * @dest: Where to copy the string to51Testing软件测试网#ih7yN!~~es
* @src: Where to copy the string from
hXsLv5kR,UQ#M6w0 * @count: The maximum number of bytes to copy
,]+[^qn`^0 *51Testing软件测试网@1B6C;A Q.x-U
* The result is not %NUL-terminated if the source exceeds
* @count bytes.
*/
QKkH}h @l3_c'k0char * strncpy(char * dest,const char *src,size_t count)51Testing软件测试网zQW|3h
{
D WJ4x*W#v/e?0 char *tmp = dest;

,X#Z5j5H8FsAfU0 while (count) {
  if ((*tmp = *src) != 0) src++;
r3AQ@ x0s2bmQM/W0  tmp++;
1vqT'|EC*jN+g0  count--;
}
7W-c*xJ CC0 return dest;
0@(O pzS|8M0}

RJK!c%S0　　而memmove函数是这样描写的

R1~(MGf3c'd'N0 51Testing软件测试网 ^qQKJGR

Khs5QdB[0/**
TZ^1`lq-u0 * memmove - Copy one area of memory to another51Testing软件测试网J,MI2E!i3J{)E
* @dest: Where to copy to
Y%`~6c(u:Y2h)J&w0 * @src: Where to copy from
* @count: The size of the area.
*51Testing软件测试网_Y#gng/Fa
* Unlike memcpy(), memmove() copes with overlapping areas.51Testing软件测试网I&C:aD.Ax
*/
/J!V#h(vr]p0void * memmove(void * dest,const void *src,size_t count)
K.?$v D&kL e0{
'?E T2?{E$`(X7r0 char *tmp, *s;

.\O%D2Rj,G"E7~ U0 if (dest <= src) {
  tmp = (char *) dest;
NNR7M5Wi8sZ0  s = (char *) src;
c*n"YL1b$l0  while (count--)
rfP9HlX#T0   *tmp++ = *s++;
  }
WZ3ZWL u0[YU8C0 else {
  tmp = (char *) dest + count;
a#~)U#E-@T\0  s = (char *) src + count;51Testing软件测试网 u~T;H?nQ3r
  while (count--)51Testing软件测试网v JMr:cvH(s
   *--tmp = *--s;51Testing软件测试网%K3CJwr gY8]
  }51Testing软件测试网~i hR{