# typeid().name()

typeid().name()是一个工具函数，可以返回对象或者表达式的类型，该函数位于头文件 `<typeinfo>` 中，所以需要包含。typeid()接受一个对象或者表达式，返回一个名为type_info的标准库类型的对象的应用，type_info中存储了特定类型的有关信息。typeid().name()以c-style字符串形式返回类型名。typeid()其实是一个单目操作符。

```c++
#include<iostream>  
#include <typeinfo>  
using namespace std;  

class Class1{};
class Class2:public Class1{};
void fn0();
int fn1(int n);

int main(void)  
{  
    int a = 10;
    int* b = &a;
    float c;
    double d;

    cout << typeid(a).name() << endl;
    cout << typeid(b).name() << endl;
    cout << typeid(c).name() << endl;
    cout << typeid(d).name() << endl;
    cout << typeid(Class1).name() << endl;
    cout << typeid(Class2).name() << endl;
    cout << typeid(fn0).name() << endl;
    cout << typeid(fn1).name() << endl;
    cout << typeid(typeid(a).name()).name() << endl;
    system("pause");
}  

```

typeid().name()可以返回变量、函数、类的数据类型名，功能相当强大的。`cout << typeid(typeid(a).name()).name() << endl;`可以看到结果为`char const *`，因此typeid().name()返回了存储类型名的字符串。

在编译程序时需要注意，使用MSVC和GCC编译后程序运行的结果有所不同。如果我们使用MSVC编译，那么输出的名称都是完整的名称，结果如下：

```bash
int
int *
float
double
class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >
bool
char
short
char const *
```

如果使用的是GCC编译的结果，那么输出的名称都是缩写的名称，结果如下：

```bash
i
Pi
f
d
NSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE
```


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