C++类可以不显示声明构造函数，在创建类对象时编译器自动调用默认的构造函数...

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#include "stdafx.h"

#include <string>
#include <iostream>

using namespace std;

// 没有显示声明构造函数，编译器会调用默认的构造函数
class Test1 {
public:
	int i;
	string str;
};

// 显示声明了构造函数
class Test2 {
public:
	Test2();
	Test2(int i, string s);
	int i;
	string str;
};

Test2::Test2():i(0), str("Test2") {
	cout<<"Test2()"<<endl;
}

Test2::Test2(int i, string s):i(i), str(s) {
	cout<<"Test2(int i, string s)"<<endl;
}

int _tmain(int argc, _TCHAR* argv[])
{
	cout<<"----------------调用默认构造函数，成员变量初始值不确定----------------"<<endl;
	Test1 *t = new Test1;
	cout<<"t->i = "<<t->i<<", t->str = ["<<t->str<<"]"<<endl;
	printf("t->i = %d, t->str = [%s]n", t->i, (const char *)t->str.c_str());

	cout<<endl<<"----------------调用默认构造函数，并为其成员变量设置初始值----------------"<<endl;
	Test1 *t1 = new Test1;
	t1->i = 0;
	t1->str = "Test1";
	cout<<"t1->i = "<<t1->i<<", t1->str = ["<<t1->str<<"]"<<endl;
	printf("t1->i = %d, t1->str = [%s]n", t1->i, (const char *)t1->str.c_str());

	cout<<endl<<"----------------调用自定义的无参构造函数，在构造函数中进行初始化成员变量----------------"<<endl;
	Test2 *t2 = new Test2;
	cout<<"t2->i = "<<t2->i<<", t2->str = ["<<t2->str<<"]"<<endl;
	printf("t2->i = %d, t2->str = [%s]n", t2->i, (const char *)t2->str.c_str());

	cout<<endl<<"----------------调用自定义的有参构造函数，在构造函数中进行初始化成员变量----------------"<<endl;
	Test2 *t3 = new Test2(100, "Today is very hot!");
	cout<<"t3->i = "<<t3->i<<", t3->str = ["<<t3->str<<"]"<<endl;
	printf("t3->i = %d, t3->str = [%s]n", t3->i, (const char *)t3->str.c_str());

	int x;
	cin>>x;

	return 0;
}