如何快速识别并获取C语言变量类型的最佳方法？

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目录- 获取C++变量类型及传统方法的对比- 获取C++数据类型取值范围- 包含头文件- 类型变量定义- 类型值范围- 完整代码示例- 获取C++变量类型- 直接访问上级代码

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 <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。