std :: basic_string类型的非const引用的init无效 <char> :: const_iterator＆来自std :: basic_string类型的rvalue <char> ::为const_iterator

Question

I'm get the above error when I compile the following MWE on GCC

#include <string>

void frobnigate( const std::string& str )
{
    std::string::const_iterator& iter = str.begin();
}

int main()
{
    frobnigate( "all things!!!" );
}

Am I doing something wrong or is this a GCC issue?

Answer 1

Am I doing something wrong or is this a GCC issue?

Yes you are doing something wrong.

std::string::begin() returns a value type ( rvalue , since its a temporary). But you are trying to initialize a non-const reference from an rvalue which is illegal in C++.

You definitely want:

std::string::const_iterator iter = str.begin();

Better still:

auto iter = str.begin();

---

Iterators are cheap to copy and should be used by value, so a reference or const-reference to an iterator is frowned upon.

Answer 2

You should do this:

std::string::const_iterator iter = str.begin();

That is, remove the reference, because begin() returns a value, not a reference, and you need to manage the lifetime of that iterator (which will be a simple, small, cheap value such as a pointer).