main.cpp

#include <iostream>
#include "String.h"
using namespace std;
int main() {
	String t1("abcd");
	String t2("efg");
	cout <<"t1的大小为： "<< t1.size() << endl;
	cout << "t2的大小为： " << t2.size() << endl;
	cout << "t1+t2 的大小为： " << (t1 + t2).size() << endl;

	system("pause");
}

String.h

#define MAXLEN 128
class String {
public:
	int size()const;
	String(const char* s = "");
	String operator + (const String s);
	char & operator [] (int index);
	char operator [] (int index)const;
private:
	char buf[MAXLEN];
};

int String::size()const {
	int i = 0;
	while (buf[i] != '\0') {
		i++;
	}
	return i;
}

char & String:: operator [] (int index) {
	return buf[index];
}

char String::operator [] (int index)const {
	const char t = buf[index];
	return t;
}

String::String(const char* s) {
	int i = 0;
	while (s[i] != '\0') {
		buf[i] = s[i];
		i++;
	}
	buf[i] = '\0';
}

String String::operator + (const String s) {
	char temp[MAXLEN] = { '\0' };
	int i = 0;
	while (buf[i] != '\0') {
		temp[i] = buf[i];
		i++;
	}
	cout << s.size() << endl;
	for (int j = 0; j < s.size(); j++) {
		temp[i] = s[j];
		i++;
	}
	temp[i] = '\0';
	return String(temp);
}