C++ typeid关键字

typeid 是 C++ 的关键字之一，用于获取运行时类型信息，typeid操作符的返回结果是名为type_info的标准库类型的对象的引用（在头文件typeinfo中定义）。

上测试代码：

#include <assert.h>
#include <iostream>
#include <string>
#include <typeinfo>
#include <vector>
#include <cstdio>

using namespace std;

int func(int a) {
    return 0;
}

typedef int(*fun_ptr)(int);

class Base {
public:
    Base() {}
};

int test_typeid1() {
    char              char_ = 'a';
    unsigned char     uchar_ = 'b';
    short             short_ = -16;
    unsigned short    ushort_ = 16;
    int               int_ = -1024;
    unsigned int      uint_ = 1024;
    float             float_ = 1.2f;
    double            double_ = 2.34;
    long              long_ = -12222;
    long long         llong_ = 12222;
    int array[10] = { 0 };
    int* array_ptr = array;
    string            string_("xiongwei");
    vector<int>       int_vector;
    fun_ptr  f = func;
    Base              base_;
    Base* pBase = new Base;
    Base& rBase = base_;

    cout << "char_ type: " << typeid(char_).name() << std::endl;
    assert(typeid(char).name() == typeid(char_).name());

    std::cout << "uchar type: " << typeid(uchar_).name() << std::endl; // uchar type: unsigned char
    assert(typeid(unsigned char).name() == typeid(uchar_).name());

    std::cout << "short_ type: " << typeid(short_).name() << std::endl; // short_ type: short
    assert(typeid(short).name() == typeid(short_).name());

    std::cout << "ushort_ type: " << typeid(ushort_).name() << std::endl; // ushort_ type: unsigned short
    assert(typeid(unsigned short).name() == typeid(ushort_).name());

    std::cout << "int_ type: " << typeid(int_).name() << std::endl; // int_ type: int
    assert(typeid(int).name() == typeid(int_).name());

    std::cout << "uint_ type: " << typeid(uint_).name() << std::endl; // uint_ type: unsigned int
    assert(typeid(unsigned int).name() == typeid(uint_).name());

    std::cout << "float_ type: " << typeid(float_).name() << std::endl; // float_ type: float
    assert(typeid(float).name() == typeid(float_).name());

    std::cout << "double_ type: " << typeid(double_).name() << std::endl; // double_ type: double
    assert(typeid(double).name() == typeid(double_).name());

    std::cout << "long_ type: " << typeid(long_).name() << std::endl; // long_ type: long
    assert(typeid(long).name() == typeid(long_).name());

    std::cout << "llong_ type: " << typeid(llong_).name() << std::endl; // llong_ type: __int64
    assert(typeid(long long).name() == typeid(llong_).name());

    std::cout << "array[] type: " << typeid(array).name() << std::endl; // array[] type: int [10]
    assert(typeid(int[10]).name() == typeid(array).name());

    std::cout << "array_header type: " << typeid(array_ptr).name() << std::endl; // array_header type: int * __ptr64
    assert(typeid(int*).name() == typeid(array_ptr).name());

    std::cout << "string_ type: " << typeid(string_).name() << std::endl; // string_ type: class std::basic_string<char,struct std::char_traits<char>, class std::allocator<char>>
    assert(typeid(std::string).name() == typeid(string_).name());

    std::cout << "int_vector type: " << typeid(int_vector).name() << std::endl; // int_vector type: class std::vector<int,class std::allocator<int>>
    assert(typeid(std::vector<int>).name() == typeid(int_vector).name());

    std::cout << "f type: " << typeid(f).name() << std::endl; // f type : int(__cdecl*)(int)
    assert(typeid(int(*)(int)).name() == typeid(f).name());

    std::cout << "Base_ type: " << typeid(base_).name() << std::endl; // Base_ type: class Base
    assert(typeid(class Base).name() == typeid(base_).name());

    std::cout << "pBase_ type: " << typeid(pBase).name() << std::endl; // pBase_ type: class Base * __ptr64
    assert(typeid(class Base*).name() == typeid(pBase).name());

    std::cout << "rBase_ type: " << typeid(rBase).name() << std::endl; // Base__ type: class Base
    assert(typeid(class Base&).name() == typeid(rBase).name());
    return 0;

}

void test_typeid2() {

    struct Base {

    }; // non-polymorphic
    struct Derived : Base {

    };

    struct Base2 {
        virtual void foo() {}
    }; // polymorphic

    struct Derived2 : Base2 {

    };

    int myint = 50;
    std::string mystr = "string";
    double *mydoubleptr = NULL;

    std::cout << "myint has type: " << typeid(myint).name() << '\n' // myint has type: int
        << "mystr has type: " << typeid(mystr).name() << '\n' // mystr has type: class std::basic_string<char, struct std::char_traits<char>, class std::allocator<char>>
        << "mydoubleptr has type: " << typeid(mydoubleptr).name() << '\n'; // mydoubleptr has type: double * __ptr64

                                                                           // std::cout << myint is a glvalue expression of polymorphic type; it is evaluated
    const std::type_info& r1 = typeid(std::cout); // 50

    std::cout << "#std::cout<<myint has type : " << r1.name() << '\n';
    // std::cout<<myint has type: class std::basic_ostream<char, struct std::char_traits<char>>

    const std::type_info& r2 = typeid(std::printf("%d\n", myint));
    std::cout << "printf(\"%d\\n\",myint) has type : " << r2.name() << '\n'; // printf(\"%d\\n\",myint) has type : int

    Derived d1;
    Base& b1 = d1;
    std::cout << "reference to non-polymorphic base: " << typeid(b1).name() << '\n'; // reference to non-polymorphic base: struct 'int __cdecl test_typeid2(void)'::'2'::Base

    Derived2 d2;
    Base2& b2 = d2;
    std::cout << "reference to polymorphic base: " << typeid(b2).name() << '\n'; // reference to polymorphic base: struct 'int __cdecl test_typeid2(void)'::'3'::Derived2

    try {
        // dereferencing a null pointer: okay for a non-polymoprhic expression  
        std::cout << "mydoubleptr points to " << typeid(*mydoubleptr).name() << '\n'; // mydoubleptr points to double  
                                                                                      // dereferencing a null pointer: not okay for a polymorphic lvalue  
        Derived2* bad_ptr = NULL;
        std::cout << "bad_ptr points to...";  // bad_ptr points to...   
        std::cout << typeid(*bad_ptr).name() << '\n';
    }
    catch (const std::bad_typeid& e) {
        std::cout << " caught " << e.what() << '\n'; // caught Attempted a typeid of NULL pointer!  
    }

}

template < typename T >
T max(T arg1, T arg2) {
    std::cout << typeid(T).name() << "s compared." << std::endl;
    return (arg1 > arg2 ? arg1 : arg2);
}

int test_typeid3()
{
    class Base {
    public:
        virtual void vvfunc() {}
    };

    class Derived : public Base {};

    Derived* pd = new Derived;
    Base* pb = pd;
    std::cout << typeid(pb).name() << std::endl;   //prints "class Base *" // class 'int __cdecl test_typeid3(void)'::'2'::Base * __ptr64  
    std::cout << typeid(*pb).name() << std::endl;   //prints "class Derived" // class 'int __cdecl test_typeid3(void)'::'2'::Derived  
    std::cout << typeid(pd).name() << std::endl;   //prints "class Derived *" // class 'int __cdecl test_typeid3(void)'::'2'::Derived * __ptr64  
    std::cout << typeid(*pd).name() << std::endl;   //prints "class Derived" // class 'int __cdecl test_typeid3(void)'::'2'::Derived  
    delete pd;

    float a = 1.2, b = 3.4;
    max(a, b); // floats compared  

    max<int>(1,2);

    return 0;
}

int main() {

    test_typeid1();
    cout << "---------------------------------------" << endl;
    test_typeid2();
    test_typeid3();

    system("pause");
    return 0;
}