在C ++中无法读取科学的d表示法 [英] Scientific `d` notation not read in C++

问题描述

我需要读取一个数字格式的数据文件：

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任何想法吗？

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/标头来管理这种格式，但是我找不到它。

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

由Fortran程序生成的文件报告双精度数字（以科学计数法表示）使用

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

所以您的选择是：

1. 预处理Fortran数据文件（一个简单的 Search and Replace 就足够了）。



2. 使用类似以下内容的东西：

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;
}

也：

• 看看使用 D读取ASCII数字而不是 E用C表示科学计数法（是C，但您知道了）；


• 仔细检查输入文件，因为Fortran可以删除'E'/'D'（请参见< a href = https://stackoverflow.com/questions/24004824/for-three-digit-exponents-fortran-drops-the-e-in-the-output>对于三位数的指数，Fortran将 E放入输出和如何在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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