错误：从类型'std :: vector< bool> :: reference {aka std :: _ Bit_reference}'的右值对类型'bool&'的非常量引用进行了无效的初始化 [英] error: invalid initialization of non-const reference of type ‘bool&’ from an rvalue of type ‘std::vector<bool>::reference {aka std::_Bit_reference}’
问题描述
为什么会出现错误：从类型为 std :: vector :: reference {aka std :: _ Bit_reference}的右值对 bool&类型的非常量引用进行无效的初始化？
Why do I get the error: invalid initialization of non-const reference of type ‘bool&’ from an rvalue of type ‘std::vector::reference {aka std::_Bit_reference}’?
vector<vector<bool>> vis;
bool& visited(int x, int y)
{
return vis[x][y]; //error
}
据我所知，vector中的operator []返回引用，因此它应该是一个左值，但不起作用。我应该怎么做才能使其正常工作？
As far as I know operator[] in vector returns reference, so it should be an lvalue, but it doesn't work. What should I do to make it work?
推荐答案
那是因为 std :: vector< bool> 不是它的样子。
That's because std::vector< bool > is not what it looks like.
std有一个 specialization :: vector 类型为 bool -已对空间进行了优化，并且每个元素都使用了一位。
There's a specialization for std::vector with type bool - it's space optimized and uses a single bit for each element.
如果需要此功能，可以尝试使用 uint8_t 或类似的方法。或者只返回 bool ，而不是 bool& 。
You can try to use uint8_t or something like this, if you need this functionality. Or just return bool, not bool&.
operator [] 返回的引用不是标准引用，而是代理类，这使这里的事情变得复杂。
The reference, returned by operator[] is not a standard reference, but a proxy class, which complicates the things here.
这里有很多类似的问题：
There are a lot of similar questions about this here:
- 运算符| = on std :: vector< bool>
- 为什么vector< bool> :: reference不返回对bool的引用？
- < a href = https://stackoverflow.com/questions/6781985/is-the-use-of-stdvectorbool-objects-in-c-acceptable-or-should-i-use-an-al>正在使用std :: vector< bool>的可以使用C ++中的对象，还是应该使用替代对象？
- operator |= on std::vector<bool>
- Why vector<bool>::reference doesn't return reference to bool?
- Is the use of std::vector<bool> objects in C++ acceptable, or should I use an alternative?
以及其他。了解有关 std :: vector<的更多信息。 bool> 专业化。
And others. Read more about std::vector< bool > specialization.
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