问题源于同事的一个问题，VC编译器里如何查看double的最大值? 他在limits.h里没找到。
在limits.h里面，只可以看到整型的最大值，但是看不到浮点数的最大值。浮点数的最大值可以这样得到:
#include <iostream>
#include <limits>
using namespace std;
// compile with: /EHsc
int main(){
cout << numeric_limits<double>::max() << endl;
}
运行平台为VS2008,如果出现max编译冲突，可以加上#undef max。
模板类numeric_limits的声明是:
template <typename T>
numeric_limits<T>
// 变量和成员函数 // // has_denorm // has_denorm_loss // has_infinity // has_quiet_NaN // has_signaling_NaN // is_bounded // is_exact // is_iec559 // is_integer // is_modulo // is_signed // is_specialized // tinyness_before // traps // round_style // digits // digits10 // max_exponent // max_exponent10 // min_exponent // min_exponent10 // radix; // denorm_min() // epsilon() // infinity() // max() // min() // quiet_ NaN() // round_error() // signaling_NaN() //////////////////////////////////////////////////////////////////////
实例代码：
#include <iostream>
#include <limits>
using namespace std;
int main() {
cout << " 1 The minimum value for char is " <<
(int)numeric_limits<char>::min() << endl;
cout << " 2 The minimum value for int is " <<
numeric_limits<int>::min() << endl;
cout << " 3 The maximum value for char is " <<
(int)numeric_limits<char>::max() << endl;
cout << " 4 The maximum value for int is " <<
numeric_limits<int>::max() << endl;
cout << " 5 The number of bits to represent a char is " <<
numeric_limits<char>::digits << endl;
cout << " 6 The number of bits to represent an int is " <<
numeric_limits<int>::digits << endl;
cout <<" 7 The number of digits representable in base 10 for float is "
<< numeric_limits<float>::digits10 << endl;
cout << " 8 Is a char signed? " <<
numeric_limits<char>::is_signed << endl;
cout << " 9 Is an unsigned integer signed? " <<
numeric_limits<unsigned int>::is_signed << endl;
cout << "10 Is an integer an integer? " <<
numeric_limits<int>::is_integer << endl;
cout << "11 Is a float an integer? " <<
numeric_limits<float>::is_integer << endl;
cout << "12 Is an integer exact? " <<
numeric_limits<int>::is_exact << endl;
cout << "13 Is a float exact? " <<
numeric_limits<float>::is_exact << endl;
cout << "14 The radix for float is " <<
numeric_limits<float>::radix << endl;
cout << "15 The epsilon for float is " <<
numeric_limits<float>::epsilon() << endl;
cout << "16 The round error for float is " <<
numeric_limits<float>::round_error() << endl;
cout << "17 The minimum exponent for float is " <<
numeric_limits<float>::min_exponent << endl;
cout << "18 The minimum exponent in base 10 " <<
numeric_limits<float>::min_exponent10 << endl;
cout << "19 The maximum exponent is " <<
numeric_limits<float>::max_exponent << endl;
cout << "20 The maximum exponent in base 10 " <<
numeric_limits<float>::max_exponent10 << endl;
cout << "21 Can float represent positive infinity? " <<
numeric_limits<float>::has_infinity << endl;
cout << "22 Can double represent positive infinity? " <<
numeric_limits<double>::has_infinity << endl;
cout << "23 Can int represent positive infinity? " <<
numeric_limits<int>::has_infinity << endl;
cout << "24 Can float represent a NaN? " <<
numeric_limits<float>::has_quiet_NaN << endl;
cout << "25 Can float represent a signaling NaN? " <<
numeric_limits<float>::has_signaling_NaN << endl;
cout << "26 Does float allow denormalized values? " <<
numeric_limits<float>::has_denorm << endl;
cout << "27 Does float detect denormalization loss? " <<
numeric_limits<float>::has_denorm_loss << endl;
cout << "28 Representation of positive infinity for float " <<
numeric_limits<float>::infinity() << endl;
cout << "29 Representation of quiet NaN for float " <<
numeric_limits<float>::quiet_NaN() << endl;
cout << "30 Minimum denormalized number for float " <<
numeric_limits<float>::denorm_min() << endl;
cout << "31 Minimum positive denormalized value for float " <<
numeric_limits<float>::denorm_min() << endl;
cout << "32 Does float adhere to IEC 559 standard? " <<
numeric_limits<float>::is_iec559 << endl;
cout << "33 Is float bounded? " <<
numeric_limits<float>::is_bounded << endl;
cout << "34 Is float modulo? " <<
numeric_limits<float>::is_modulo << endl;
cout << "35 Is int modulo? " <<
numeric_limits<float>::is_modulo << endl;
cout << "36 Is trapping implemented for float? " <<
numeric_limits<float>::traps << endl;
cout << "37 Is tinyness detected before rounding? " <<
numeric_limits<float>::tinyness_before << endl;
cout << "38 What is the rounding style for float? " <<
(int)numeric_limits<float>::round_style << endl;
cout << "39 What is the rounding style for int? " <<
(int)numeric_limits<int>::round_style << endl;
cout << "40 How does a float represent a signaling NaN? " <<
numeric_limits<float>::signaling_NaN() << endl;
cout << "41 Is int specialized? " <<
numeric_limits<float>::is_specialized << endl;
}
请运行相关的代码查看结果。