用 C++ 创建一个简单的配置文件和解析器

问题描述

我正在尝试创建一个看起来像这样的简单配置文件

I am trying to create a simple configuration file that looks like this

url = http://mysite.com
file = main.exe
true = 0

当程序运行时，我希望它将配置设置加载到下面列出的程序变量中.

when the program runs, I would like it to load the configuration settings into the programs variables listed below.

string url, file;
bool true_false;

我做了一些研究，这个链接似乎有帮助(nucleon 的帖子)，但我似乎无法让它工作，而且我的理解太复杂了.有没有一种简单的方法可以做到这一点?我可以使用 ifstream 加载文件，但这是我自己所能得到的.谢谢！

I have done some research and this link seemed to help (nucleon's post) but I can't seem to get it to work and it is too complicated to understand on my part. Is there a simple way of doing this? I can load the file using ifstream but that is as far as I can get on my own. Thanks!

推荐答案

一般来说，解析此类典型的配置文件最容易分两个阶段:首先读取行，然后逐行解析.
在 C++ 中，可以使用 std::getline() 从流中读取行.虽然默认情况下它会读到下一个 ' '(它会消耗，但不会返回)，你也可以给它传递一些其他的分隔符，这使它成为阅读的好选择up-to-some-char，比如你的例子中的 = .

In general, it's easiest to parse such typical config files in two stages: first read the lines, and then parse those one by one.
In C++, lines can be read from a stream using std::getline(). While by default it will read up to the next ' ' (which it will consume, but not return), you can pass it some other delimiter, too, which makes it a good candidate for reading up-to-some-char, like = in your example.

为简单起见，以下假设 = not 被空格包围.如果你想在这些位置允许空格，你必须有策略地放置 is >>std::ws 在读取值并从键中删除尾随空格之前.但是，对于配置文件阅读器来说，IMO 在语法上增加的一点灵活性并不值得.

For simplicity, the following presumes that the = are not surrounded by whitespace. If you want to allow whitespaces at these positions, you will have to strategically place is >> std::ws before reading the value and remove trailing whitespaces from the keys. However, IMO the little added flexibility in the syntax is not worth the hassle for a config file reader.

const char config[] = "url=http://example.com
"
                      "file=main.exe
"
                      "true=0";

std::istringstream is_file(config);

std::string line;
while( std::getline(is_file, line) )
{
  std::istringstream is_line(line);
  std::string key;
  if( std::getline(is_line, key, '=') )
  {
    std::string value;
    if( std::getline(is_line, value) ) 
      store_line(key, value);
  }
}

(添加错误处理留给读者作为练习.)

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