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获取C++变量类型的简单方法

来源：互联网收集：自由互联发布时间：2023-02-01

目录获取C++变量类型与传统方法的对比获取C++数据类型取值范围包含头文件类型变量定义取类型值范围完整代码获取C++变量类型直接上代码 #include type_traits#include typeinfo#include m

获取C++变量类型

直接上代码

#include <type_traits>
#include <typeinfo>
#include <memory>
#include <string>
#include <cstdlib>
#include <iostream>
#ifndef _MSC_VER
#include <cxxabi.h>
#endif

using namespace std;

template <class T>
string type_name()
{
    typedef typename remove_reference<T>::type TR;
    unique_ptr<char, void (*)(void *)> own(
#ifndef _MSC_VER
        abi::__cxa_demangle(typeid(TR).name(), nullptr, nullptr, nullptr),
#else
        nullptr,
#endif
        free);
    string r = own != nullptr ? own.get() : typeid(TR).name();
    if (is_const<TR>::value)
        r += " const";
    if (is_volatile<TR>::value)
        r += " volatile";
    if (is_lvalue_reference<T>::value)
        r += "&";
    else if (is_rvalue_reference<T>::value)
        r += "&&";
    return r;
}

int main()
{
    int a = 1;
    const int &b = a;
    cout << type_name<decltype(b)>() << endl;
}

定义了一个模板函数type_name()，可以对传入的模板类型T进行类型判断，结合指针、左值/右值引用、常类型，准确得出变量的类型。在调用该函数时使用了decltype关键字，传入待确定的变量，然后输出变量类型。

以上运行的结果为

int const&

如果要输出int指针的类型：

int main()
{
    int a = 1;
    int* b = &a;
    cout << type_name<decltype(b)>() << endl;
}

结果为：

int*

可以看出该函数得出的结果是非常准确而又精简的。

与传统方法的对比

传统输出C++类型的方法是使用typeid(var).name()，其弊端在于输出的结果不完整或者过于冗长。

例如：

1. 传统方法打印int类型

#include <iostream>

int main()
{
  int a = 10;
  std::cout << typeid(a).name() << std::endl;
}

运行结果为：

i

只得到了int的缩写i。

2. 传统方法打印string类型

#include <iostream>
#include <string>

int main()
{
  std::string a = "abc";
  std::cout << typeid(a).name() << std::endl;
}

运行结果为：

NSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE

过于冗长，不便于看出类型名称。

3. 传统方法打印引用类型

#include <iostream>

int main()
{
  int a0 = 23;
  int& a = a0;
  std::cout << typeid(a).name() << std::endl;
}

运行结果为：

i

并没有准确地输出我们想要的结果。

总结：使用了稍微复杂的模板函数，可以准确输出C++的变量类型，而非大多数人提到的type_id(var).name()打印出来的结果有各种不恰当的地方。

获取C++数据类型取值范围

包含头文件

#include <limits>
#include <float.h>

类型变量定义

int a = 2;//32位整数 4字节 4byte  32bit
    unsigned int b = 2u;//无符号32位整数  4字节 4byte  32bit
    signed int b1 = -2147483648;//有符号32位整数  4字节 4byte  32bit
    long c = 2l;//32位整数 4字节 4byte  32bit
    unsigned long d= 2ul;//无符号32位整数 4字节 4byte  32bit
    double e = 2.0;//双精度浮点数
    float f = 2.0f;//单精度浮点数
    long double g=2.0l;//长双精度浮点数
    long long h=2ll;//超长整数 64位整数 8字节 8byte  64bit
    short i = 2;//16位整数 2字节 2byte  16bit
    unsigned short i1 = 2;//无符号16位整数 2字节 2byte  16bit
    char j = '2';//字符类型 1字节 1byte  8bit
    char j1 = '2';//无符号字符类型 1字节 1byte  8bit

取类型值范围

std::cout <<"int a is :"<< a << "  int类型取值范围:" <<INT_MIN <<","<<INT_MAX <<"\n"
              <<"signed int b1 is :"<< b1 << "  int类型取值范围: " <<INT_MIN <<","<<INT_MAX <<"\n"
              <<"unsigned int b is : "<<b << "  unsigned int类型取值范围: " <<0 <<","<<UINT_MAX <<"\n"
              <<"long c is : "<<c<<"  long类型取值范围: " <<LONG_MIN <<","<<LONG_MAX <<"\n"
              <<"unsigned long d is : "<<d<<"  unsigned long类型取值范围: " <<0 <<","<<ULONG_MAX <<"\n"
              <<"double e is : "<<e<< "  double类型取值范围:" <<DBL_MIN <<","<<DBL_MAX <<"\n"
              <<"float f is : "<<f<<"  float类型取值范围:" <<FLT_MIN <<","<<FLT_MAX <<"\n"
              <<"long double g is : "<<g<<"  long double类型取值范围:" <<LDBL_MIN <<","<<LDBL_MAX <<"\n"
              <<"long long h is : "<<h<<"  long long类型取值范围: " <<LLONG_MIN <<","<<LLONG_MAX <<"\n"
              <<"short i is : "<<i<<"  short类型取值范围: " <<SHRT_MIN <<","<<SHRT_MAX <<"\n"
              <<"unsigned short i is : "<<i1<<"  unsigned short类型取值范围: " <<0 <<","<<USHRT_MAX <<"\n"
              <<"char j is : "<<j<<"  char类型取值范围: " <<CHAR_MIN <<","<<CHAR_MAX <<"\n"
              <<"unsigned char j1 is : "<<j1<<" unsigned char类型取值范围: " <<0 <<","<<UCHAR_MAX <<"\n";

输出效果：

int a is :2 int类型取值范围:-2147483648,2147483647
signed int b1 is :-2147483648 int类型取值范围: -2147483648,2147483647
unsigned int b is : 2 unsigned int类型取值范围: 0,4294967295
long c is : 2 long类型取值范围: -9223372036854775808,9223372036854775807
unsigned long d is : 2 unsigned long类型取值范围: 0,18446744073709551615
double e is : 2 double类型取值范围:2.22507e-308,1.79769e+308
float f is : 2 float类型取值范围:1.17549e-38,3.40282e+38
long double g is : 2 long double类型取值范围:3.3621e-4932,1.18973e+4932
long long h is : 2 long long类型取值范围: -9223372036854775808,9223372036854775807
short i is : 2 short类型取值范围: -32768,32767
unsigned short i is : 2 unsigned short类型取值范围: 0,65535
char j is : 2 char类型取值范围: -128,127
unsigned char j1 is : 2 unsigned char类型取值范围: 0,255

完整代码

#include <iostream>
#include <chrono>
#include <thread>
#include <limits>
#include <float.h>
 
int main() {
    int a = 2;//32位整数 4字节 4byte  32bit
    unsigned int b = 2u;//无符号32位整数  4字节 4byte  32bit
    signed int b1 = -2147483648;//有符号32位整数  4字节 4byte  32bit
    long c = 2l;//32位整数 4字节 4byte  32bit
    unsigned long d= 2ul;//无符号32位整数 4字节 4byte  32bit
    double e = 2.0;//双精度浮点数
    float f = 2.0f;//单精度浮点数
    long double g=2.0l;//长双精度浮点数
    long long h=2ll;//超长整数 64位整数 8字节 8byte  64bit
    short i = 2;//16位整数 2字节 2byte  16bit
    unsigned short i1 = 2;//无符号16位整数 2字节 2byte  16bit
    char j = '2';//字符类型 1字节 1byte  8bit
    char j1 = '2';//无符号字符类型 1字节 1byte  8bit
    //进度表示写法
    int bin2 =0b11111111;//二进制 0和1 前缀:0b  stdc++ 14
    int bin8 = 077;//八进制  0~7  前缀:0
    int bin16= 0xff;//十六进制 0~F 前缀:0x
    int aa = INT_MAX * 2 + 1;
    unsigned  int bb = UINT_MAX;
    if (aa == bb)
    {
        std::cout<<UINT_MAX<<std::endl;
    }
    std::cout <<"int a is :"<< a << "  int类型取值范围:" <<INT_MIN <<","<<INT_MAX <<"\n"
              <<"signed int b1 is :"<< b1 << "  int类型取值范围: " <<INT_MIN <<","<<INT_MAX <<"\n"
              <<"unsigned int b is : "<<b << "  unsigned int类型取值范围: " <<0 <<","<<UINT_MAX <<"\n"
              <<"long c is : "<<c<<"  long类型取值范围: " <<LONG_MIN <<","<<LONG_MAX <<"\n"
              <<"unsigned long d is : "<<d<<"  unsigned long类型取值范围: " <<0 <<","<<ULONG_MAX <<"\n"
              <<"double e is : "<<e<< "  double类型取值范围:" <<DBL_MIN <<","<<DBL_MAX <<"\n"
              <<"float f is : "<<f<<"  float类型取值范围:" <<FLT_MIN <<","<<FLT_MAX <<"\n"
              <<"long double g is : "<<g<<"  long double类型取值范围:" <<LDBL_MIN <<","<<LDBL_MAX <<"\n"
              <<"long long h is : "<<h<<"  long long类型取值范围: " <<LLONG_MIN <<","<<LLONG_MAX <<"\n"
              <<"short i is : "<<i<<"  short类型取值范围: " <<SHRT_MIN <<","<<SHRT_MAX <<"\n"
              <<"unsigned short i is : "<<i1<<"  unsigned short类型取值范围: " <<0 <<","<<USHRT_MAX <<"\n"
              <<"char j is : "<<j<<"  char类型取值范围: " <<CHAR_MIN <<","<<CHAR_MAX <<"\n"
              <<"unsigned char j1 is : "<<j1<<" unsigned char类型取值范围: " <<0 <<","<<UCHAR_MAX <<"\n";
 
    std::cout<<"二进制0b11111111值是:"<<bin2<<std::endl;
    std::cout<<"八进制077值是:"<<bin8<<std::endl;
    std::cout<<"十六进制0xff值是:"<<bin16<<std::endl;
 
 
    std::cout << "等待5秒后退出程序" <<std::endl;
    std::this_thread::sleep_for(std::chrono::seconds(5));
 
    return 0;
}

以上为个人经验，希望能给大家一个参考，也希望大家多多支持自由互联。

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获取C++变量类型的简单方法

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