重载 C++ 的示例提取运算符>>解析数据

发布于 2024-08-04 06:30:34 字数 1138 浏览 6 评论 0原文

我正在寻找一个很好的示例，说明如何重载流输入运算符（运算符>>）以使用简单的文本格式解析一些数据。我已阅读本教程，但我想做一些更高级的事情。就我而言，我有固定的字符串，我想检查（并忽略）。假设链接中的 2D 点格式更像

Point{0.3 =>
      0.4 }

是解析出数字 0.3 和 0.4 的预期效果。（是的，这是一个非常愚蠢的语法，但它包含了我需要的几个想法）。大多数情况下，我只是想看看如何正确检查固定字符串是否存在，忽略空格等。

更新： 哎呀，我在下面发表的评论没有格式（这是我第一次使用这个网站）。我发现可以用类似

std::cin >> std::ws;

And 之类的方法跳过空格，因为

static bool match_string(std::istream &is, const char *str){
    size_t nstr = strlen(str);
    while(nstr){
        if(is.peek() == *str){
            is.ignore(1);
            ++str;
            --nstr;
        }else{
            is.setstate(is.rdstate() | std::ios_base::failbit);
            return false;
        }
    }
    return true;
}

现在如果能够获取解析错误的位置（行号），那就太好了。

更新2： 仅使用 1 个字符前瞻即可实现行号和注释解析。最终结果可以在 AArray.cpp 中的 parse() 函数中看到。该项目是一个可（反）序列化的 C++ PHP 类数组类。

原文

I am looking for a good example of how to overload the stream input operator (operator>>) to parse some data with simple text formatting. I have read this tutorial but I would like to do something a bit more advanced. In my case I have fixed strings that I would like to check for (and ignore). Supposing the 2D point format from the link were more like

Point{0.3 =>
      0.4 }

where the intended effect is to parse out the numbers 0.3 and 0.4. (Yes, this is an awfully silly syntax, but it incorporates several ideas I need). Mostly I just want to see how to properly check for the presence of fixed strings, ignore whitespace, etc.

Update:
Oops, the comment I made below has no formatting (this is my first time using this site).
I found that whitespace can be skipped with something like

std::cin >> std::ws;

And for eating up strings I have

static bool match_string(std::istream &is, const char *str){
    size_t nstr = strlen(str);
    while(nstr){
        if(is.peek() == *str){
            is.ignore(1);
            ++str;
            --nstr;
        }else{
            is.setstate(is.rdstate() | std::ios_base::failbit);
            return false;
        }
    }
    return true;
}

Now it would be nice to be able to get the position (line number) of a parsing error.

Update 2:
Got line numbers and comment parsing working, using just 1 character look-ahead. The final result can be seen here in AArray.cpp, in the function parse(). The project is a (de)serializable C++ PHP-like array class.

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