获取C++中数据的类型的方法

本文最后更新于：2022年3月19日 凌晨

此文来自于👉 C++ / typeinfo — DevDocs ，并整理

判断数据是哪种数据类型#

头文件<typeinfo>

std::type_info::name()#

例子：

#include <iostream>
#include <typeinfo>
 
struct Base { virtual ~Base() = default; };
struct Derived : Base {};
 
int main() {
    Base b1;
    Derived d1;

    const Base *pb = &b1;
    std::cout << typeid(*pb).name() << '\n';
    pb = &d1;
    std::cout << typeid(*pb).name() << '\n';

    int i;
    int * pi;
    std::cout << "int is: " << typeid(int).name() << '\n';
    std::cout << "  i is: " << typeid(i).name() << '\n';
    std::cout << " pi is: " << typeid(pi).name() << '\n';
    std::cout << "*pi is: " << typeid(*pi).name() << '\n';

    return 0;

}

结果：

4Base
7Derived

int is: int
  i is: int
 pi is: int *
*pi is: int

判断数据是否是对应的数据类型#

头文件<type_traits>

主要类型类别 Primary type categories#

  • is_array

    Is array (class template )

    // is_array example
#include <iostream>
#include <array>
#include <string>
#include <type_traits>

int main() {
    std::cout << std::boolalpha;
    std::cout << "is_array:" << std::endl;
    std::cout << "int: " << std::is_array<int>::value << std::endl;
    std::cout << "int[3]: " << std::is_array<int[3]>::value << std::endl;
    std::cout << "array<int,3>: " << std::is_array<std::array<int,3>>::value << std::endl;
    std::cout << "string: " << std::is_array<std::string>::value << std::endl;
    std::cout << "string[3]: " << std::is_array<std::string[3]>::value << std::endl;
    return 0;
}

    结果：

    is_array:
int: false
int[3]: true
array<int,3>: false
string: false
string[3]: true

  • is_class

    Is non-union class (class template )

  • is_enum

    Is enum (class template )

  • is_floating_point

    Is floating point (class template )

  • is_function

    Is function (class template )

  • is_integral

    Is integral (class template )

  • is_lvalue_reference

    Is lvalue reference (class template )

  • is_member_function_pointer

    Is member function pointer (class template )

  • is_member_object_pointer

    Is member object pointer (class template )

  • is_pointer

    Is pointer (class template )

  • is_rvalue_reference

    Is rvalue reference (class template )

  • is_union

    Is union (class template )

  • is_void

    Is void (class template )

复合类型范畴 Composite type categories#

  • is_arithmetic

    Is arithmetic type (class template )

    // is_arithmetic example
#include <iostream>
#include <type_traits>
#include <complex>

int main() {
    std::cout << std::boolalpha;
    std::cout << "is_arithmetic:" << std::endl;
    std::cout << "char: " << std::is_arithmetic<char>::value << std::endl;
    std::cout << "float: " << std::is_arithmetic<float>::value << std::endl;
    std::cout << "float*: " << std::is_arithmetic<float*>::value << std::endl;
    std::cout << "complex<double>: " << std::is_arithmetic<std::complex<double>>::value << std::endl;
    return 0;
}

Output:

is_arithmetic:
char: true
float: true
float*: false
complex<double>: false

类型属性 Type properties#

  • is_abstract

    Is abstract class (class template )

    // is_abstract example
#include <iostream>
#include <type_traits>

struct A { };
struct B {
  	virtual void fn() = 0;  // pure virtual function
};
struct C : B { };
struct D : C { virtual void fn(){} };

int main() {
    std::cout << std::boolalpha;
    std::cout << "is_abstract:" << std::endl;
    std::cout << "A: " << std::is_abstract<A>::value << std::endl;
    std::cout << "B: " << std::is_abstract<B>::value << std::endl;
    std::cout << "C: " << std::is_abstract<C>::value << std::endl;
    std::cout << "D: " << std::is_abstract<D>::value << std::endl;
    return 0;
}

结果：

is_abstract:
A: false
B: true
C: true
D: false

类型特征 Type features#

  • has_virtual_destructor

    Has virtual destructor (class template )

    // has_virtual_destructor example
#include <iostream>
#include <type_traits>

struct A { };
struct B { virtual ~B(){} };
struct C : B { };

int main() {
    std::cout << std::boolalpha;
    std::cout << "has_virtual_destructor:" << std::endl;
    std::cout << "int: " << std::has_virtual_destructor<int>::value << std::endl;
    std::cout << "A: " << std::has_virtual_destructor<A>::value << std::endl;
    std::cout << "B: " << std::has_virtual_destructor<B>::value << std::endl;
    std::cout << "C: " << std::has_virtual_destructor<C>::value << std::endl;
    return 0;
}

Output:

has_virtual_destructor:
int: false
A: false
B: true
C: true

类型关系 Type relationships#

  • is_base_of

    Is base class of (class template )

    // is_base_of example
#include <iostream>
#include <type_traits>

struct A {};
struct B : A {};

int main() {
    std::cout << std::boolalpha;
    std::cout << "is_base_of:" << std::endl;
    std::cout << "int, int: " << std::is_base_of<int,int>::value << std::endl;
    std::cout << "A, A: " << std::is_base_of<A,A>::value << std::endl;
    std::cout << "A, B: " << std::is_base_of<A,B>::value << std::endl;
    std::cout << "A, const B: " << std::is_base_of<A,const B>::value << std::endl;
    std::cout << "A&, B&: " << std::is_base_of<A&,B&>::value << std::endl;
    std::cout << "B, A: " << std::is_base_of<B,A>::value << std::endl;
    return 0;
}

Output:

is_base_of:
int, int: false
A, A: true
A, B: true
A, const B: true
A&, B&: false
B, A: false
C++ Type

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