自定义字符串类String,实现运算符重载,内存管理

1、String.h

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#pragma once
#include <iostream>
using namespace std;
 
class String {
	friend ostream &operator < < (ostream &, String &);
private:
	char *m_name = NULL;
	char *setM_name(const char *cstring);
	char *strAppend(const char *, const char *);
public:
	String(const char *cstring = "");
	String(const String &);
	~String();
	bool operator == (String &string);
	String &operator = (String &string);
	String &operator = (const char *cstring);
	String operator + (const char *cstring);
	String operator + (const String &string);
	String &operator += (const char *cstring);
	String &operator += (const String &string);
	char operator[](int index);
	bool operator<(const String &string);
};
 
ostream &operator << (ostream &cout, String &string);

2、String.cpp

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#include "String.h"
 
String::String(const char *name) 
{
	operator=(name);
}
 
String::String(const String &str) 
{
	operator=(str.m_name);
}
 
String::~String()
{
	operator=(NULL);
}
 
bool String::operator == (String &str) 
{
	return m_name == str.m_name;
}
 
String &String::operator = (String &str) 
{
	return operator=(str.m_name);
}
 
String &String::operator = (const char *name) 
{
	m_name = setM_name(name);
	return *this;
}
 
 
String String::operator + (const String &string) 
{
	return operator+(string.m_name);
}
String String::operator + (const char *cstring)
{
	String newString;
	return newString += cstring;
}
 
String &String::operator += (const String &string)
{
	return operator+=(string.m_name);
}
String &String::operator += (const char *cstring) 
{
	char *str = strAppend(m_name, cstring);
	if (str) {
		setM_name(NULL);
		m_name = str;
	}
	return *this;
}
 
char String::operator[](int index) 
{
	if (m_name == NULL || index < 0 || index >= strlen(m_name)) return '\0';
	return m_name[index];
}
 
bool String::operator<(const String &string)
{
	int res = strcmp(m_name, string.m_name);
	return res < 0;
}
char *String::setM_name(const char *cstring) 
{
	if (m_name == cstring) return m_name;
	if (m_name) {
		cout << "delete - " << m_name << endl;
		delete[] m_name;
		m_name = NULL;
	}
	if (cstring) {
		m_name = new char[strlen(cstring) + 1];
		strcpy(m_name, cstring);
		cout << "new - " << m_name << endl;
	}
	return m_name;
}
 
 
char *String::strAppend(const char *str1, const char *str2) 
{
	if (str1 == NULL || str2 == NULL) return NULL;
	char *str = new char[strlen(str1) + strlen(str2) + 1]();
	strcat(str, str1);
	strcat(str, str2);
	cout << "new - " << str << endl;
	return str;
}
 
ostream &operator << (ostream &cout, String &str) 
{
	return cout << str.m_name;
}

3、main.cpp

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#include <iostream>
#include "String.h"
using namespace std;
 
int main() {
	{
		String str1 = "123";
		String str2 = "456";
		String str3 = str1;
		str1 = str1;
		str1 = str2;
	}
	system("pause");
	return 0;
}

4、执行结果:

new – 123
new – 456
new – 123
delete – 123
new – 456
delete – 123
delete – 456
delete – 456
请按任意键继续. . .

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