1. numeric_limits是什么？

一般来说，数值型别的极值是一个与平台相关的特性。C++标准程序库通过template numeric_limits提供这些极值，取代传统C语言，所采用的预处理常数。新的极值概念有两个优点，第一是提供更好的型别安全性，第二是程序员可借此写出一些template以核定这些极值。

2. 小例展示numeric_limits的基本用法：

#include 
    
       #include 
     
        using namespace std;    int main() {      cout << boolalpha;        cout << "max(short): " << numeric_limits
      
       ::max() << endl;      cout << "min(short): " << numeric_limits
       
        ::min() << endl;        cout << "max(int): " << numeric_limits
        
         ::max() << endl;      cout << "min(int): " << numeric_limits
         
          ::min() << endl; cout << "max(long): " << numeric_limits
          
           ::max() << endl; cout << "min(long): " << numeric_limits
           
            ::min() << endl; cout << endl; cout << "max(float): " << numeric_limits
            
             ::max() << endl; cout << "min(float): " << numeric_limits
             
              ::min() << endl; cout << "max(double): " << numeric_limits
              
               ::max() << endl; cout << "min(double): " << numeric_limits
               
                ::min() << endl; cout << "max(long double): " << numeric_limits
                
                 ::max() << endl; cout << "min(long double): " << numeric_limits
                 
                  ::min() << endl; cout << endl; cout << "is_signed(char): " << numeric_limits
                  
                   ::is_signed << endl; cout << "is_specialized(string): " << numeric_limits
                   
                    ::is_specialized << endl; }
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     
    

我机器上的运行结果：

max(short): 32767  

min(short): -32768  

max(int): 2147483647  

min(int): -2147483648  

max(long): 2147483647  

min(long): -2147483648  

max(float): 3.40282e+038  

min(float): 1.17549e-038  

max(double): 1.79769e+308  

min(double): 2.22507e-308  

max(long double): 1.79769e+308  

min(long double): 2.22507e-308  

is_signed(char): true  

is_specialized(string): false  

请按任意键继续. . .