是否可以构造字符串中部分的可修改视图? [英] Is it possible to construct a modifiable view of portion in a string?

问题描述

我有一个匹配表，其中包含数组的一部分(在回调中)的开始和结束索引-我将该数组包装到字符串向量中-现在最近我确实需要修改字符串的原始部分./p>

I have a match table with start and end indices of portions, in array (in a callback) - I wrap that array into vector of strings - now recently I did have the need to modify the original portions of the string.

struct regexcontext {

    std::vector<std::optional<std::string>> matches;

    std::string subject;
};

int buildmatchvector(size_t(*offset_vector)[2], int max, regexcontext* pcontext) {
    pcontext->matches.clear();
    ranges::transform(ranges::span{ offset_vector, max }, std::back_inserter(pcontext->matches), [&](const auto& refarr) {
        return refarr[0] == -1 ? std::optional<std::string> {} : std::optional<std::string>{ pcontext->subject.substr(refarr[0], refarr[1] - refarr[0]) };
        });
    return 0;
}

是否可以通过修改匹配向量来更改上述定义，我也将修改主题字符串.

Is it possible to change the above definition in a way that by modifying the match vector I will modify the subject string as well.

我听说过字符串视图，但也听说不能用可变大小的字符串修改它.

I've heard of string view but I've also heard it can't be modified with a variable sized string.

请注意，我使用的是 ranges-v3 ，这是目前唯一实现标准范围的库，另外还使用了非标准的 ranges :: span msvc(由于某些原因 std :: span 在该处不起作用).

Note I'm using ranges-v3 which is the only library that implements standard ranges at the moment plus the nonstandard ranges::span which allows me to compile on msvc (since std::span doesn't work there for some reason).

推荐答案

只要您只需要将字符更改为其他字符，而无需添加或删除字符，则可以使用 span .支持添加或删除将更加复杂，我认为标准库中没有任何简单的解决方案.示例:

As long as you only need to change characters to others, but not add or remove characters, then you could use a vector of span. Supporting addition or removal would be much more complicated and I don't think there's any simple solution in the standard library. Example:

return refarr[0] == -1
    ? span<char> {}
    : span<char> {
        &pcontext->subject[refarr[0]],
        refarr[1] - refarr[0]
    };

请注意，对指向的字符串进行的任何无效操作都会使这些范围无效，因此将字符串设为私有是个好主意.

Note that any invalidating operation on the pointed string would invalidate these spans, so it would be a good idea to make the string private.

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