my_string-part1

my_strlen

int my_strlen(char * str)
{
    int len = 0;
    char * temp = str;
    while((*temp) != '\0')
    {
        temp++;
        len++;
    }    
    
    return len;
}

my_strcmp

int my_strcmp(char * str1,char * str2)
{
    char * s1 = str1;
    char * s2 = str2;
    
    while(*s1 != '\0')
    {
        if(((*s1) > (*s2)) || (*s2 == '\0'))
        {
            return 1;
        }
        if((*s1) < (*s2))
        {
            return -1;
        }
    }
    
    if(*s2 != '\0')
    {
        return -1;
    }
    else
    {
        return 0;
    }
}

my_strcat

void my_strcat(char * str,char * dest)
{
    char * s = str;
    char * d = dest;
    
    while((*s) != '\0')
    {
        s++;
    }
    
    while((*d) != '\0')
    {
        *s = *d;
        s++;
        d++;
    }
    
}

以上代码并未做入口参数检查及地址有效性检查，改进版本将在之后发布。