学步园

<limits>包含所有标准数据类型的上下限信息

 numeric_limit<类型名>::min(),  max() , digits 

min()整型和浮点数类型最小值含义不同，整型会得到真正的最小值，即带符号的负数

对于浮点数类型返回可以存储的最小正数 

 digits返回二进制数字位数，带符号的整数类型，返回除符号位之外的二进制数字的位数

对于浮点数类型返回尾数钟二进制数字的位数 

 digits10返回十进制数字位数，带符号的整数类型，返回除符号位之外的十进制数字的位数

对于浮点数类型返回尾数中十进制数字的位数 

// Program 3.3 Finding maximum and minimum values for data types
#include <limits>
#include <iostream>
using std::cout;
using std::endl;
using std::numeric_limits;

int main() {
  cout << endl
       << "The range for type short is from "
       << numeric_limits<short>::min()
       << " to "
       << numeric_limits<short>::max();
  cout << endl << numeric_limits<short>::digits;
    cout << endl << numeric_limits<short>::digits10;
  cout << endl
       << "The range for type int is from "
       << numeric_limits<int>::min()
       << " to "
       << numeric_limits<int>::max();
  cout << endl << numeric_limits<int>::digits;
    cout << endl << numeric_limits<int>::digits10;
  cout << endl
       << "The range for type long is from "
       << numeric_limits<long>::min()
       << " to "
       << numeric_limits<long>::max();
  cout << endl << numeric_limits<long>::digits;
  cout << endl << numeric_limits<long>::digits10;
  cout << endl
       << "The range for type float is from "
       << numeric_limits<float>::min()
       << " to "
       << numeric_limits<float>::max();
  cout << endl << numeric_limits<float>::digits;
  cout << endl << numeric_limits<float>::digits10;
  cout << endl
       << "The range for type double is from "
       << numeric_limits<double>::min()
       << " to "
       << numeric_limits<double>::max();
  cout << endl << numeric_limits<double>::digits;
   cout << endl << numeric_limits<double>::digits10;
  cout << endl
       << "The range for type long double is from "
       << numeric_limits<long double>::min()
       << " to "
       << numeric_limits<long double>::max();
  cout << endl << numeric_limits<long double>::digits;
  cout << endl << numeric_limits<long double>::digits10;
  cout << endl;
  return 0;
}

 以下代码使用了unsigned char且采用do...while形式

for(unsigned char ch=0;ch<=std::numeric_limits<unsigned char>::max();ch++) //不能使用这种形式，因为ch等于最大值时，加1后下一个值为0，是个死循环 
// Program 5.9 Using the continue statement
#include <iostream>
#include <iomanip>
#include <cctype>
#include <limits>
using std::cout;
using std::endl;
using std::setw;

int main() {
  // Output the column headings
  cout << endl
       << setw(13) << "Character  "
       << setw(13) << "Hexadecimal "
       << setw(13) << "Decimal   "
       << endl;

  cout << std::uppercase;                      // Uppercase hex digits

  unsigned char ch = 0;                        // Character code

  // Output characters and corresponding codes
  do {
    if(!std::isprint(ch))                      // If it does not print
      continue;                                // skip this iteration

    cout << setw(7)  << ch
         << std::hex                           // Hexadecimal mode
         << setw(13) << static_cast<int>(ch)
         << std::dec                           // Decimal mode
         << setw(13) << static_cast<int>(ch)
         << endl;
  } while(ch++ < std::numeric_limits<unsigned char>::max());
    return 0;
}