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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;
}原文鏈接：https://blog.csdn.net/sky4403/article/details/123028385
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