獲取C++變量類型的簡(jiǎn)單方法

更新時(shí)間：2022年09月28日 09:55:11 作者：漫游宇宙sky

這篇文章主要介紹了獲取C++變量類型的簡(jiǎn)單方法，具有很好的參考價(jià)值，希望對(duì)大家有所幫助。如有錯(cuò)誤或未考慮完全的地方，望不吝賜教

獲取C++變量類型

直接上代碼

#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;
}

定義了一個(gè)模板函數(shù)type_name()，可以對(duì)傳入的模板類型T進(jìn)行類型判斷，結(jié)合指針、左值/右值引用、常類型，準(zhǔn)確得出變量的類型。在調(diào)用該函數(shù)時(shí)使用了decltype關(guān)鍵字，傳入待確定的變量，然后輸出變量類型。

以上運(yùn)行的結(jié)果為

int const&

如果要輸出int指針的類型：

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

結(jié)果為：

int*

可以看出該函數(shù)得出的結(jié)果是非常準(zhǔn)確而又精簡(jiǎn)的。

與傳統(tǒng)方法的對(duì)比

傳統(tǒng)輸出C++類型的方法是使用typeid(var).name()，其弊端在于輸出的結(jié)果不完整或者過(guò)于冗長(zhǎng)。

例如：

1. 傳統(tǒng)方法打印int類型

#include <iostream>

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

運(yùn)行結(jié)果為：

i

只得到了int的縮寫i。

2. 傳統(tǒng)方法打印string類型

#include <iostream>
#include <string>

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

運(yùn)行結(jié)果為：

NSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE

過(guò)于冗長(zhǎng)，不便于看出類型名稱。

3. 傳統(tǒng)方法打印引用類型

#include <iostream>

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

運(yùn)行結(jié)果為：

i

并沒(méi)有準(zhǔn)確地輸出我們想要的結(jié)果。

總結(jié)：使用了稍微復(fù)雜的模板函數(shù)，可以準(zhǔn)確輸出C++的變量類型，而非大多數(shù)人提到的type_id(var).name()打印出來(lái)的結(jié)果有各種不恰當(dāng)?shù)牡胤健?/p>

獲取C++數(shù)據(jù)類型取值范圍

包含頭文件

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

類型變量定義

int a = 2;//32位整數(shù) 4字節(jié) 4byte  32bit
    unsigned int b = 2u;//無(wú)符號(hào)32位整數(shù)  4字節(jié) 4byte  32bit
    signed int b1 = -2147483648;//有符號(hào)32位整數(shù)  4字節(jié) 4byte  32bit
    long c = 2l;//32位整數(shù) 4字節(jié) 4byte  32bit
    unsigned long d= 2ul;//無(wú)符號(hào)32位整數(shù) 4字節(jié) 4byte  32bit
    double e = 2.0;//雙精度浮點(diǎn)數(shù)
    float f = 2.0f;//單精度浮點(diǎn)數(shù)
    long double g=2.0l;//長(zhǎng)雙精度浮點(diǎn)數(shù)
    long long h=2ll;//超長(zhǎng)整數(shù) 64位整數(shù) 8字節(jié) 8byte  64bit
    short i = 2;//16位整數(shù) 2字節(jié) 2byte  16bit
    unsigned short i1 = 2;//無(wú)符號(hào)16位整數(shù) 2字節(jié) 2byte  16bit
    char j = '2';//字符類型 1字節(jié) 1byte  8bit
    char j1 = '2';//無(wú)符號(hào)字符類型 1字節(jié) 1byte  8bit

取類型值范圍

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

輸出效果：

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

完整代碼

#include <iostream>
#include <chrono>
#include <thread>
#include <limits>
#include <float.h>
 
int main() {
    int a = 2;//32位整數(shù) 4字節(jié) 4byte  32bit
    unsigned int b = 2u;//無(wú)符號(hào)32位整數(shù)  4字節(jié) 4byte  32bit
    signed int b1 = -2147483648;//有符號(hào)32位整數(shù)  4字節(jié) 4byte  32bit
    long c = 2l;//32位整數(shù) 4字節(jié) 4byte  32bit
    unsigned long d= 2ul;//無(wú)符號(hào)32位整數(shù) 4字節(jié) 4byte  32bit
    double e = 2.0;//雙精度浮點(diǎn)數(shù)
    float f = 2.0f;//單精度浮點(diǎn)數(shù)
    long double g=2.0l;//長(zhǎng)雙精度浮點(diǎn)數(shù)
    long long h=2ll;//超長(zhǎng)整數(shù) 64位整數(shù) 8字節(jié) 8byte  64bit
    short i = 2;//16位整數(shù) 2字節(jié) 2byte  16bit
    unsigned short i1 = 2;//無(wú)符號(hào)16位整數(shù) 2字節(jié) 2byte  16bit
    char j = '2';//字符類型 1字節(jié) 1byte  8bit
    char j1 = '2';//無(wú)符號(hào)字符類型 1字節(jié) 1byte  8bit
    //進(jìn)度表示寫法
    int bin2 =0b11111111;//二進(jìn)制 0和1 前綴:0b  stdc++ 14
    int bin8 = 077;//八進(jìn)制  0~7  前綴:0
    int bin16= 0xff;//十六進(jìn)制 0~F 前綴: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類型取值范圍:" <<INT_MIN <<","<<INT_MAX <<"\n"
              <<"signed int b1 is :"<< b1 << "  int類型取值范圍: " <<INT_MIN <<","<<INT_MAX <<"\n"
              <<"unsigned int b is : "<<b << "  unsigned int類型取值范圍: " <<0 <<","<<UINT_MAX <<"\n"
              <<"long c is : "<<c<<"  long類型取值范圍: " <<LONG_MIN <<","<<LONG_MAX <<"\n"
              <<"unsigned long d is : "<<d<<"  unsigned long類型取值范圍: " <<0 <<","<<ULONG_MAX <<"\n"
              <<"double e is : "<<e<< "  double類型取值范圍:" <<DBL_MIN <<","<<DBL_MAX <<"\n"
              <<"float f is : "<<f<<"  float類型取值范圍:" <<FLT_MIN <<","<<FLT_MAX <<"\n"
              <<"long double g is : "<<g<<"  long double類型取值范圍:" <<LDBL_MIN <<","<<LDBL_MAX <<"\n"
              <<"long long h is : "<<h<<"  long long類型取值范圍: " <<LLONG_MIN <<","<<LLONG_MAX <<"\n"
              <<"short i is : "<<i<<"  short類型取值范圍: " <<SHRT_MIN <<","<<SHRT_MAX <<"\n"
              <<"unsigned short i is : "<<i1<<"  unsigned short類型取值范圍: " <<0 <<","<<USHRT_MAX <<"\n"
              <<"char j is : "<<j<<"  char類型取值范圍: " <<CHAR_MIN <<","<<CHAR_MAX <<"\n"
              <<"unsigned char j1 is : "<<j1<<" unsigned char類型取值范圍: " <<0 <<","<<UCHAR_MAX <<"\n";
 
    std::cout<<"二進(jìn)制0b11111111值是:"<<bin2<<std::endl;
    std::cout<<"八進(jìn)制077值是:"<<bin8<<std::endl;
    std::cout<<"十六進(jìn)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;
}

以上為個(gè)人經(jīng)驗(yàn)，希望能給大家一個(gè)參考，也希望大家多多支持腳本之家。

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