C/C++ 判断一个变量的类型(typeid)

Posted 2021-10-04 cpp_learner

当有某一个变量，你不知道他是什么类型，且你有需要知道他是什么类型时，就可以使用typeid关键字进行判断！

操作如下：

1. 判断int类型

   int in = 10;
   if (typeid(in) == typeid(int)) {
   	cout << "This '" << in << "' is a int!" << endl;
   }
   

2. 判断类

   // 类
   Student stu("小明");
   if (typeid(stu) == typeid(Student)) {
   	cout << "This '" << stu.name << "' is a Student!" << endl;
   }
   

当然你也还可以 判断其它类型这里就不列举了！

来说说具体改怎么使用：

double dou = 3.14;
if (typeid(dou) == typeid(int)) {
	cout << "This '" << dou << "' is a int!" << endl;
	
} else if (typeid(dou) == typeid(string)) {
	cout << "This '" << dou << "' is a string!" << endl;
	
} else if (typeid(dou) == typeid(double)) {
	cout << "This '" << dou << "' is a double!" << endl;

} else {
	cout << "This '" << dou << "' is not!" << endl;
}

用法如上，使用多个if else做逻辑处理，就可以得到想要的变量是什么类型了！

---

全部测试代码：

#include <iostream>
#include <string>

using namespace std;

class Student {

public:
	Student(string _name = "无名字") {
		this->name = _name;
	}
	~Student() { }

public:
	string name;
};


typedef struct Struct {
	int count = 10;
};


int main(void) {
	
	// 整形
	int in = 10;
	if (typeid(in) == typeid(int)) {
		cout << "This '" << in << "' is a int!" << endl;
	}
	
	// 字符串
	string str = "abc";
	if (typeid(str) == typeid(string)) {
		cout << "This '" << str << "' is a string!" << endl;
	}

	// 字符
	char c = 'c';
	if (typeid(c) == typeid(char)) {
		cout << "This '" << str << "' is a char!" << endl;
	}

	// 类
	Student stu("小明");
	if (typeid(stu) == typeid(Student)) {
		cout << "This '" << stu.name << "' is a Student!" << endl;
	}

	// 结构体
	typedef struct Struct structs;
	if (typeid(structs) == typeid(Struct)) {
		cout << "This 'structs' is a Struct!" << endl;
	}



	double dou = 3.14;
	if (typeid(dou) == typeid(int)) {
		cout << "This '" << dou << "' is a int!" << endl;
	
	} else if (typeid(dou) == typeid(string)) {
		cout << "This '" << dou << "' is a string!" << endl;
	
	} else if (typeid(dou) == typeid(double)) {
		cout << "This '" << dou << "' is a double!" << endl;

	} else {
		cout << "This '" << dou << "' is not!" << endl;
	}

	return 0;
}

运行截图：

---

总结：

用法还是很简单的，不过，我这里只是简单将typeid关键字的其中一个用法列举出来，其实他还有很多其它高级用法， 有兴趣的可以自行去了解了解！