你可以重用一个移动的std :: string？ [英] Can you reuse a moved std::string?

问题描述

给定此示例：

 std::vector<std::string> split(const std::string& str) {
    std::vector<std::string> result;
    std::string curr;
    for (auto c : str) {
        if (c == DELIMITER) {
            result.push_back(std::move(curr)); // ATTENTION HERE!
        } else {
            curr.push_back(c);
        }
    }
    result.push_back(std::move(curr));
    return result;
}

我可以重复使用 curr std：string？这个代码片段似乎工作： curr 被移动到
的结果向量中，它变为空。

Can I reuse the curr std:string? This snippet seems working: after curr is moved inside the result vector, it becomes empty. I want to be sure this is not an undefined behavior in the standard and it isn't working only because of luck.

推荐答案

我想确定这不是标准中未定义的行为，除了少数例外（例如智能指针），移动对象保留在有效但未指定的状态。

With a few exceptions (smart pointers, for instance), moved-from objects are left in a valid but unspecified state.

在 std： ：string ，它使用小字符串优化，例如，如果字符串小，没有动态分配，移动是一个副本。在这种情况下，完全有效的实现离开源字符串不变，而不会产生额外的成本清空字符串。

In a std::string that uses the small string optimization, for instance, if the string is small, there is no dynamic allocation, and a move is a copy. In that case it is perfectly valid for the implementation to leave the source string untouched, and not incur the extra cost of emptying the string.

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