c语言常用字符串函数实现

1.str_cmp函数实现

int str_cmp(const char *src, const char *dst)
{
    int ret = 0;
    while (!(ret = *(unsigned char*)src) - *(unsigned char*)dst && *dst) 
    {
        ++src;
        ++dst;
    }
    
    if (ret < 0) 
    {
        ret = -1;
    }
    else if (ret > 0) 
    {
        ret = 1;
    }
    
    return (ret);
}

2.str_cpy函数实现

char *str_cpy(char *dst, const char *src)
{
    char *address;
    
    assert((NULL != dst) && (NULL != src));
    
    address = dst;
    
    while ((*dst++ = *src++) != '\0') {
        NULL;
    }

    return address;
}

3.str_cat函数实现

char *str_cat(char *dst, const char *src)
{
    char * cp = dst;
    
    while( *cp )
        cp++;

    while(*cp++ = *src++) ;
    
    return( dst );
}

4.str_len函数实现

size_t str_len(const char * str)
{
    const char * eos = str;
    while( *eos++ );
    return (eos - str - 1);
}

5.str_rev函数实现

char * str_rev(char * string)
{
    char *start = string;
    char *left = string;
    char ch;
    
    while (*string++)
        ;
    string -= 2;
    
    while (left < string)
    {
        ch = *left;
        *left++ = *string;
        *string-- = ch;
    }
    
    return (start);
}

6.str_str函数实现