C字符串处理函数的实现

C字符串处理函数的实现（Linux）
#include <stddef.h>
char * ___strtok = NULL;
char * strcpy(char * dest,const char *src)
{
char *tmp = dest;
while ((*dest++ = *src++) != '\0')
/* nothing */;
return tmp;
}
char * strncpy(char * dest,const char *src,size_t count)
{
char *tmp = dest;
while (count-- && (*dest++ = *src++) != '\0')
/* nothing */;
return tmp;
}
char * strcat(char * dest, const char * src)
{
char *tmp = dest;
while (*dest)
dest++;
while ((*dest++ = *src++) != '\0')
;
return tmp;
}
char * strncat(char *dest, const char *src, size_t count)
{
char *tmp = dest;
if (count) {
while (*dest)
dest++;
while ((*dest++ = *src++)) {
if (--count == 0)
break;
}
}
return tmp;
}
int strcmp(const char * cs,const char * ct)
{
register signed char __res;
while (1) {
if ((__res = *cs - *ct++) != 0 || !*cs++) /*is !*cs++ necessary? incase more cmp*/
break;
}
return __res;
}
int strncmp(const char * cs,const char * ct,size_t count)
{
register signed char __res = 0;
while (count) {
if ((__res = *cs - *ct++) != 0 || !*cs++)
break;
count--;
}
return __res;
}
char * strchr(const char * s,char c)
{
for(; *s != c; ++s)
if (*s == '\0')
return NULL;
return (char *) s;
}
size_t strlen(const char * s)
{
const char *sc;
for (sc = s; *sc != '\0'; ++sc)
/* nothing */;
return sc - s;
}
size_t strnlen(const char * s, size_t count)
{
const char *sc;
for (sc = s; *sc != '\0' && count--; ++sc)
/* nothing */;
return sc - s;
}
size_t strspn(const char *s, const char *accept)
{
const char *p;
const char *a;
size_t count = 0;
for (p = s; *p != '\0'; ++p) {
for (a = accept; *a != '\0'; ++a) {
if (*p == *a)
break;
}
if (*a == '\0')
return count;
++count;
}
return count;
}
char * strpbrk(const char * cs,const char * ct)
{
const char *sc1,*sc2;
for( sc1 = cs; *sc1 != '\0'; ++sc1) {