自己实现的string的库函数

为了更好地理解string的各个库函数，现将几个常用的库函数用自己的方式实现如下：

#include<iostream>
using namespace std;
#include<cassert>

//求字符串的长度 (注：''的长度不计算在内)
int my_strlen(char* str)
{
    if (str == NULL)
    {
        return 0;
    }
    int len = 0;
    while (*str++ != '')//  ''不计算在内
    {
        len++;
    }
    return len;
}



//string比较函数
int my_strcmp(const char* str1, const char* str2)
{
    assert(str1 != NULL && str2 != NULL);
    
    if (*str1 == '' && *str2 == '')
        return 0;
    
    int result = 0;//记录比较结果：相等记录0；str1大于str2，记录1；str1小于str2，记录-1；
    
    while (*str1 != '')
    {
        if ((result = *str1 - *str2) != 0)  //  *str1!=*str2
        {
            break;
        }
        str1++;
        str2++;
    }
    if (result > 0)
        result = 1;
    else if (result < 0)
        result = -1;
    return result;
}

//查找str2是否为str1的字串，并返回str2在str1中第一次出现的位置
const char* my_strstr(const char* str1, const char* str2)
{
    assert(str1 != NULL);
    assert(str2 != NULL);
    const char* ps1 = str1;
    const char* ps2 = str2;
    while (*ps1 != '')
    {
        const char* ret = NULL;
        if (*ps1 == *ps2)
        {
            ret = ps1;
            while (*ps1++ == *ps2++)
            {
                if (*ps2 == '')
                {
                    return ret;
                }
            }
        }
        else
            ps1++;
    }
    return NULL;
}

//字符串拷贝函数
char* my_strcpy(char* dst, const char* src)
{
    assert(dst != NULL);
    assert(src != NULL);
    char* pDst = dst;         //保护参数
    const char* pSrc = src;   //保护参数
    while (*pDst != '')
    {
        *pDst++ = *pSrc++;
    }
    return dst;
}

//string 连接函数
char* my_strcat(char* dst, const char* src)
{
    assert(src != NULL && dst != NULL);

    char* pDst = dst;
    const char* pSrc = src;
    while (*pDst != '')
    {
        pDst++;
    }
    while (*pSrc != '')
    {
        *pDst++ = *pSrc++;
    }
    *pDst = '';

    return dst;
}


int main()
{
    char c1[10] = "abcd";
    char c2[10] = "98712345";
    char c3[5] = "1234";

    char c4[5] = "abcd";
    char c5[5] = "abbb";
    char c6[5] = "abcd";

    cout << "my_strlen(src):" << my_strlen(c1) << endl;

    cout << "my_strcmp(c4, c5):" << my_strcmp(c4, c5) << endl;
    cout << "my_strcmp(c4, c6):" << my_strcmp(c4, c6) << endl;
    cout << "my_strcmp(c5, c6):" << my_strcmp(c5, c6) << endl;

    const char* ret = my_strstr(c2, c3);
    cout << "my_strstr(c2, c3)=>  ret:" << ret << endl;

    my_strcpy(c2, c3);
    cout << "my_strcpy(c2, c3)=>  c3:" << c3 << endl;
    cout << "my_strcpy(c2, c3)=>  c2:" << c2 << endl;

    my_strcat(c1, c3);
    cout << "my_strcat(c1, c3)=>  c1:" << c1 << endl;
}