为什么 std::hex 和 std::oct 标志不起作用？

Question

这是我的代码：

// This program demonstrates the use of flags.

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

int main()
{
  string filename; bool tf; double number;

  cout << "Name a file to create/overwrite: ";
  cin >> filename;

  ofstream outfile (filename.c_str());

  if(outfile.fail())
  {
    cout << "Creating/Overwriting the file has failed.\nExiting...\n";
    return 1;
  }

  cout << "Give me a boolean (0/1): "; cin >> tf;
  cout << "Give me a large number with decimal points: "; cin >> number;

  outfile.setf(ios_base::boolalpha); // Turns on boolalpha flag.
  outfile << "Here's a boolean: " << tf << endl;

  outfile.unsetf(ios_base::boolalpha); // Unsets boolalpha flag.
  outfile << "Here's your number: " << number << endl;

  outfile.setf(ios_base::scientific); // Turns on scientific notation flag.
  outfile << "Here's your number is scientific notation: " << number << endl;

  outfile.setf(ios_base::fixed); // When possible, floating point numbers will not appear in scientific notation.
  outfile << "Here's your number in fixed notation: " << number << endl;

  outfile.setf(ios_base::hex); // Numbers will appear in hexadecimal format.
  outfile << "Here's your number in hexadecimal format: " << number << endl;

  outfile.setf(ios_base::oct, ios_base::uppercase); // Numbers will appear in uppercase, octal format.
  outfile << "Here's your number in octal format: " << number << endl;

  return 0;
}

当我运行这个...

test.txt的内容：

Here's a boolean: false
Here's your number: 3491.67
Here's your number is scientific notation: 3.491670e+03
Here's your number in fixed notation: 3491.67
Here's your number in hexadecimal format: 3491.67
Here's your number in octal format: 3491.67

为什么当我设置“hex”和“oct”标志时，它们不起作用？

在文本文件中，我期望在“十六进制形式：”和“八进制格式：”旁边出现“3591.67”以外的内容。

我是否错误地实现了标志？

Answer 1

不幸的是，八进制和十六进制打印仅适用于整数，而不适用于双精度数。见http://stdcxx.apache.org/doc/stdlibug/28-3.html

如果你想使用 setf，它应该是：

outfile.setf(ios_base::hex,ios_base::basefield);

。或者，在 std:hex 中使用管道，即：

outfile << std::hex;

.

Answer 2

八进制和十六进制格式仅影响整数的显示方式。如果您想查看十六进制浮点数，您可以使用hexfloat (C++11) 或使用cstdio 中的printf 函数和%a 格式化代码。

另见Dump hex float in C++