C++ 中未读取科学的“d"符号

2022-01-14 00:00:00 fortran data-files scientific-notation c++

我需要读取一个数据文件，其中的数字以如下格式写入:

I need to read a data file in which numbers are written in a format like this:

1.0d-05

C++ 似乎无法识别这种科学记数法！关于如何读取/转换这些类型的数字有什么想法吗?

C++ doesn't seem to recognize this type of scientific notation! Any ideas on how I could read/convert those types of numbers?

我需要数字(即 double/float)而不是字符串.也许已经有一个类/头来管理这种格式，但我找不到它.

I need numbers (i.e. double / float) not strings. Maybe there is already a class / header to manage this format, but I could not find it.

推荐答案

Fortran 程序生成的文件报告 双精度数(科学计数法) 使用字母 D 而不是 E.

Files produced by Fortran programs report double precision numbers (in scientific notation) using the letter D instead of E.

所以你的选择是:

  1. 预处理 Fortran 数据文件(一个简单的搜索和替换就足够了).

  2. 使用类似:

  1. Preprocess the Fortran data file (a simple Search and Replace is enough).

  2. Use something like:

#include <iostream>
#include <sstream>
#include <string>
#include <vector>

int main()
{
  std::istringstream input("+1.234000D-5 -2.345600D+0 +3.456700D-2");

  std::vector<double> result;

  std::string s;
  while (input >> s)
  {
    auto e(s.find_first_of("Dd"));
    if (e != std::string::npos)
      s[e] = 'E';

    result.push_back(std::stod(s));
  }

  for (auto d : result)
    std::cout << std::fixed << d << std::endl;

  return 0;
}

还有:

  • 看看 使用D"读取 ASCII 数字而不是E"使用 C 的科学记数法(它是 C，但你明白了)；
  • 仔细检查输入文件，因为 Fortran 可以删除E"/D"(请参阅?? 对于三位数指数，Fortran 在输出中删除E" 和 如何在 C++ 中读取 FORTRAN 格式的数字).
  • take a look at Reading ASCII numbers using "D" instead of "E" for scientific notation using C (it's C but you get the idea);
  • double check the input file since Fortran can drop the 'E' / 'D' (see For three digit exponents Fortran drops the 'E' in the output and How to read FORTRAN formatted numbers in C++).

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