c++不用库函数实现strcat（代码教程）

自己写的，就不写注视了，比较简单

#include <iostream>  
  
using namespace std;  
  
/** \brief 
 * 
 * \param 
 * \param 
 * \return 
 * 
 */  
char * mystrcat(char *s1,const char *s2);  
int lengthstr(const char *str);  
  
int main()  
{  
    char str1[20] = "abcdefg";  
    char str2[20] = "ABCDEFG";  
  
    char *a = mystrcat(str1,str2);  
    cout << str1 << endl;  
    cout << a << endl;  
  
    return 0;  
}  
  
char * mystrcat(char *s1,const char *s2)  
{  
    int s1len = lengthstr(s1);  
    int s2len = lengthstr(s2);  
  
    for(int i = s1len;i <= s1len + s2len; i++)  
    {  
        s1[i] = s2[i - s1len];  
    }  
    return s1;  
}  
  
int lengthstr(const char *str)  
{  
    int i = 0;  
    while(*(str + i) != '\0')  
    {  
        i++;  
    }  
    return i;  
}