获取C++变量类型的简单方法
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编程网。
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