原型：extern int strlen(char *s);
功能：计算字符串s的(unsigned int型）长度
说明：返回s的长度，不包括结束符NULL。
int strlen(const char *str)
{
if(!str)return 0;
const char *p = str;
while(*p++);
return p - str - 1;
}int strlenN(const char *str)
{
unsigned int i = 0;
if(!str)return i;
for (i = 0; *str != ‘\0‘; i++,*str++);
return i;
}
原型：extern char *strcat(char *dest,char *src);
功能：把src所指字符串添加到dest结尾处(覆盖dest结尾处的‘\0‘)并添加‘\0‘。
说明：src和dest所指内存区域不可以重叠且dest必须有足够的空间来容纳src的字符串。
返回指向dest的指针。
char *strcat(char *dest,char *src)
{
char* cp = dest;
while(*cp)
cp++;
while(*cp++ = *src++); //*cp == ‘\0‘;
return(dest);
}int strcmp(const char *str1, const char *str2)
{
register signed char __res;
while(1)
{
if((__res = *str1 - *str2++) != 0 || !*str1++)
break;
}
if (__res == 0)return __res;
__res = __res>0?1:-1;
return __res;
}
char* strcpy(char* dest,const char* src)
{
char *tmp = dest;
while ((*dest++ = *src++) != ‘\0‘);//pde = dest;
return tmp;
}
char *strncpy(char* dest,const char* src,size_t count)
{
char *tmp = dest;
size_t available = count;
while ((*dest++ = *src++) != ‘\0‘ && --available > 0);
return tmp;
}char *strset(char *s, char c)
{
char *p = s;
while (*s)
*s++ = c;
return(p);
}void* memcpy(void* pDest, const void* pSrc, unsigned int nCount)
{
if (pDest == NULL && pSrc == NULL)
return pDest;
unsigned char* pTmpD = (unsigned char*)pDest + nCount;
const unsigned char* pTmpS = (unsigned char*)pSrc + nCount;
while (nCount--)
{
*--pTmpD = *--pTmpS;
}
return pDest;
}void * memset(void* buffer,char c,size_t count)
{
char *xs = (char*) buffer;
while(count--)
*xs++ = c;
return buffer;
} void *memchr(const void *buf, char ch, size_t count)
{
const unsigned char *p = (const unsigned char *) buf;
while (count--)
{
if ((unsigned char)ch == *p++)
{
return (void *)(p-1);
}
}
return NULL;
}void * memmove(void * dest,const void *src,size_t count)
{
char *tmp, *s;
if (dest <= src /* || (char*)dest >= (char*)src+count */ ) //dest < (char*)src+count 唯一条件 会有带值现象
{
tmp = (char *) dest;
s = (char *) src;
while (count--)
*tmp++ = *s++;
} //保证dest 所付的值 src不被用到即可 由于反拷贝并
不影响
else // (char*)dest >= (char*)src+count 的现象 也可省略 这个
{ //使他在反拷贝中实现 保证 函数的调用速度
tmp = (char *) dest + count;
s = (char *) src + count; //保证下标０的位置在首位被用到所以先自减一再赋值
while (count--)
*--tmp = *--s;
}
return dest;
} #pragma pack(push,1) #pragma pack(pop)
#pragma once
原文：http://blog.csdn.net/priest18/article/details/21088349