[英]C++ How to iterate through a std::vector of objects and show content on console
For循环应该遍历std :: vector并填充内容。
First for循环给出了一条错误消息:
没有找到二元运算符<<不可转换
vector<MyClass>classVector;
for (vector<MyClass>::iterator i = classVector.begin();
i != classVector.end();
++i)
{
cout << *i << endl;
}
MyClass.h:
class MyClass{
private:
string newTodayTaskString;
public:
MyClass(string t) : newTodayTaskString (t){}
~MyClass(){}
};
这个for循环遍历字符串向量并且完美地工作。 为什么?
vector<string>stringVector;
for (vector<string>::iterator i = stringVector.begin();
i != stringVector.end();
++i)
{
cout<<*i<<endl;
}
这个问题与迭代无关,只是因为你可以写
std::string s = "Hello";
std::cout << s;
但不是
MyClass o("Hello");
std::cout << o;
请参阅如何正确重载ostream的<<运算符? 关于如何重载operator <<
使其工作!
如果您希望能够直接调用std::cout::operator <<
则需要为您的类重载流操作std::cout::operator <<
。
您可以将其定义为:
std::ostream& operator << (std::ostream& stream, const MyClass& obj)
{
stream << obj.newTodayTaskString;
}
并将此运算符声明为朋友,以便它可以访问类的私有成员或为您的类提供打印功能并使用它。
我想你想要打印一个类的成员,而不是类本身。
例如:
cout << (*i).Name << endl;
你应该重载输出操作符。
#include <iostream>
#include <string>
#include <vector>
#include <iterator>
class MyClass{
private:
std::string newTodayTaskString;
public:
explicit MyClass(const std::string t) : newTodayTaskString (t){}
std::ostream& print(std::ostream& os) const { return os << newTodayTaskString; }
~MyClass(){}
};
std::ostream& operator << (std::ostream& os, const MyClass& obj)
{
return obj.print(os);
}
int main()
{
std::vector<MyClass> vec = {MyClass("add"), MyClass("clear")};
std::copy(vec.begin(), vec.end(), std::ostream_iterator<MyClass>(std::cout, "\n"));
}
你正在迭代“MyClass”的向量,这可能是用户定义的类型。所以你必须告诉编译器你感兴趣的“MyClass”类的数据。下面是一个示例代码 - 仅用于理解目的
// Temp_Practice.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include<iostream>
#include<memory>
#include<ostream>
#include <vector>>
using namespace std;
// This example is just for understanding/Demo purpose.
// it will not run on any compiler
class MyClass {
public:
std::string _name;
std::string _address;
int _age;
// Constructor
public:
MyClass() {}
MyClass(std::string name, std::string address, int age) :_name(name), _address(address), _age(age) {}
//Destructor
//..
// other stuff
friend ostream& operator << (ostream& os, std::string _input);
};
ostream& operator << (ostream& os, std::string _input)
{
os << _input.c_str();
return os;
}
int main()
{
std::vector<MyClass> vecMyClass;
MyClass temp("AA", "BB", 1);
vecMyClass.push_back(temp);
MyClass temp1("CC", "DD", 2);
vecMyClass.push_back(temp1);
MyClass temp2("EE", "FF", 3);
vecMyClass.push_back(temp2);
MyClass temp3("GG", "HH", 4);
vecMyClass.push_back(temp3);
MyClass temp4("II", "JJ", 5);
vecMyClass.push_back(temp4);
MyClass temp5("KK", "LL", 6);
vecMyClass.push_back(temp5);
std::vector<MyClass>::iterator itr;
for ( itr = vecMyClass.begin(); itr != vecMyClass.end(); ++itr)
{
// Compiler throws error; it does not know what programer wants to print. So its
// programer responsiblity to let compiler know what to be printed
//std::cout << itr << std::endl; // Error!!!!
// Correct Code
std::cout << itr->_name << itr->_address << itr->_age << std::endl;
}
return 0;
}
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