为什么这个迭代器比较失败？

Question

Please see the following code:

if((pos = find()) != _sym.end())
{
    // do stuff
}

pos is a scoped variable of type std::vector<T>::const_iterator where T is a POD-struct containing a pair of the same type of iterator.

_sym is a private class member variable of type std::vector<T> .

The example code throws a runtime assertion error with the message Expression: vector iterators incompatible under Visual Studio 2013. The error occurs in <vector> at line 240.

On the other hand, if I re-write the code:

pos = find();
if(pos != _sym.end()) // do stuff

then, disco.

I'm fairly sure that comparing an initialized iterator (such as end() ) with an uninitialized iterator causes this assertion; What I don't understand is if/how pos is not considered in an initialized state when the comparison operator is executed.

Answer 1

This might be relevant.

Why am I getting "vector iterators incompatible"?

I don't suppose find() changes _sym.end()?