c++不用库函数实现strcat

#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;
}