c stdlib 库函数

1 memcpy Copy one area of memory to another

void *memcpy(void *dest, const void *src, size_t count)

{

char *tmp = dest;

const char *s = src;

while (count--)

*tmp++ = *s++;

return dest;

}

2 memmove  Copy one area of memory to another

void *memmove(void *dest, const void *src, size_t count)

{

char *tmp;

const char *s;

if (dest <= src) {

tmp = dest;

s = src;

while (count--)

*tmp++ = *s++;

} else {

tmp = dest;

tmp += count;

s = src;

s += count;

while (count--)

*--tmp = *--s;

}

return dest;

}

3 memcmp

int memcmp(const void *cs, const void *ct, size_t count)

{

const unsigned char *su1, *su2;

int res = 0;

for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)

if ((res = *su1 - *su2) != 0)

break;

return res;

}

4 strcmp

int strcmp(const char *cs, const char *ct)

{

signed char __res;

while (1) {

if ((__res = *cs - *ct++) != 0 || !*cs++)

break;

}

return __res;

}