c语言字符串处理函数

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;

assert((dest!= NULL) && (src!= NULL));

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) {
for( sc2 = ct; *sc2 != '/0'; ++sc2) {
if (*sc1 == *sc2)
return (char *) sc1;
}
}
return NULL;
}

char * strtok(char * s,const char * ct)
{
char *sbegin, *send;

sbegin = s ? s : ___strtok;
if (!sbegin) {
return NULL;
}
sbegin += strspn(sbegin,ct);
if (*sbegin == '/0') {
___strtok = NULL;
return( NULL );
}
send = strpbrk( sbegin, ct);
if (send && *send != '/0')
*send++ = '/0';
___strtok = send;
return (sbegin);
}

void * memset(void * s,char c,size_t count)
{
char *xs = (char *) s;

while (count--)
*xs++ = c;

return s;
}

char * bcopy(const char * src, char * dest, int count)
{
char *tmp = dest;

while (count--)
*tmp++ = *src++;

return dest;
}
void * memcpy(void * dest,const void *src,size_t count)
{
void * ret = dest;

while(count--)

{

*(char*)dest = *(char*)src;

dest = (char *)dest + 1;

src = (char *)src + 1;

}

return ret;

}

void * memmove(void * dest,const void *src,size_t count)
{
char *tmp, *s;

if (dest <= src) {
tmp = (char *) dest;
s = (char *) src;
while (count--)
*tmp++ = *s++;
}
else {
tmp = (char *) dest + count;
s = (char *) src + count;
while (count--)
*--tmp = *--s; /*12345678*/
} /*12345678*/

return dest;
}

int memcmp(const void * cs,const void * ct,size_t count)
{
const unsigned char *su1, *su2;
signed char res = 0;

for( su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)
if ((res = *su1 - *su2) != 0)
break;
return res;
}

/*
* find the first occurrence of byte 'c', or 1 past the area if none
*/
void * memscan(void * addr, unsigned char c, size_t size)
{
unsigned char * p = (unsigned char *) addr;

while (size) {
if (*p == c)
return (void *) p;
p++;
size--;
}
return (void *) p;
}

void main(void)
{
return;
}
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