string函数的一些实现

/*************************************************************************
    > File Name: test.cpp
 ************************************************************************/
#include"stdlib.h"
#include"stdio.h"
#include"string.h"

char *mystrcat(char *dest,const char *src)
{
    char* temp = dest;
    while(*dest != '\0')
    {
        dest++;
    }

    while((*dest++ = *src++) != '\0');

    return temp;
}
char *mystrncat(char *dest,const char *src,size_t n)
{
    
    char* temp = dest;
    while(*dest != '\0')
    {
        dest++;
    }

    while(n-->0 && (*dest++ = *src++) != '\0');

    return temp;
}



void* mymemset(void *s, int c, size_t n )
{
    unsigned char uc = c;
    unsigned char *su = (unsigned char*)s;
    while(n-->0)
    {
        *su = uc;
        su++;
    }
}

int mystrlen(const char* str)
{
    return *str?(mystrlen(++str)+1):0;
    /*
    const char* eos = str;
    while(*eos++);
    return (eos-str-1);
    */
}

void* mymemcpy(void*dst, const void* src,size_t size)
{
    
    if(src==NULL || dst==NULL) return NULL;
    void* ret = dst;
    while(size--)
    {
        *(char*)dst = *(char*)src;
        dst = (char*)dst + 1;
        src = (char*)src + 1;
    }
    return ret;
}

void* mymemmove(void*dst, const void* src,size_t size)
{
    if(src==NULL || dst==NULL) return NULL;
    char* psrc;
    char* pdst;
    //存在覆盖，自后向前进行拷贝
    if((src<dst) && (char*)src+size > (char*)dst)
    {
        psrc = (char*)src + size-1;
        pdst = (char*)dst + size-1;
        while(size--)
            *pdst-- = *psrc--;
    }
    else
    {
        psrc = (char*)src;
        pdst = (char*)dst;
        while(size--)
        {
            *pdst++ = *psrc++;
        }
    }
}

int mymemcmp(const void * ptr1, const void * ptr2, size_t num)
{
    if(ptr1==NULL || ptr2==NULL || num<0) return 0;

    char* pch1 = (char*)ptr1;
    char* pch2 = (char*)ptr2;

    while(num-- && *pch1++ == *pch2++);
    return (pch1-pch2)<<8;
}

int mystrcmp ( const char * str1, const char * str2 )
{
    if(str1==NULL || str2 ==NULL) return 0;

    while(*str1 == *str2)
    {
        str1++;
        str2++;
    }

    return (*str1-*str2);
}

int mystrncmp( const char * str1, const char * str2, size_t num )
{

    if(str1==NULL || str2 ==NULL) return 0;

    while(num-- && *str1 == *str2)
    {
        str1++;
        str2++;
    }

    return (*str1-*str2);
}

int main()
{
    char ch1[] = "hello";
    char ch2[] = "herld";
 //   printf("strcat : %s\n", mystrncat(ch1,ch2,2));
    
    printf("%d\n",mystrcmp(ch2,ch1));

    printf("%d\n",mystrncmp(ch2,ch1,4));


    return 0;
}