面试中常考的几个C库函数

//内存移动

void *MemmoveEx (void *dest, const void *src, size_t len)

{

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

char *d = (char *)dest;

const char *s = (char *)src;

if (d < s)

while (len--)

*d++ = *s++;

else

{

char *lasts = (char *)s + (len-1);

char *lastd = (char *)d + (len-1);

while (len--)

*lastd-- = *lasts--;

}

return dest;

}

//内存拷贝

void * MemcpyEx (void *dest, const void *src, size_t len)

{

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

char *d = (char *)dest;

const char *s = (char *)src;

while (len--)

*d++ = *s++;

return dest;

}

//内存填充

void *MemsetEx (void *dest, int val, size_t len)

{

assert(dest!=NULL);

char *ptr = (char *)dest;

while (len-- > 0)

*ptr++ = val;

return dest;

}

//字符串拷贝

char *StrcpyEx (char *d, const char *s)

{

assert( (d != NULL) && (s != NULL) );

char *r = d;

while ((*d++ = *s++)!='\0');

return r;

}