std::vector reference error C2440

mireiner

Hi there,

I'm using Qt 5.9.7 with Visual Studio 2017 64bit compiler or alternative Visual Studio 2017 with Qt Viusal Studio Tools 2.2.2 programming Windows desktop application.

I got a problem in Qt using vector references.

The code below runs fine as pure Visual Studio 2017 C++ console application.

But the same code gives the C2440 error message if it is compiled in Qt Creator as C++ console application (without QT), as Qt console application or as simple QWidget application. The same happens if the code is compiled in Visual Studio as Qt application.

//
#include <iostream>
#include <vector>

int main()
{
    std::vector<int> vec { 0,1,2,3 };
    for (auto& v = vec.begin(); v != vec.end(); v++)
    {
    }

    return 0;
}

The error message is:
error C2440: "Initialisation": "std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Ty>>>" can't be converted to "std::_Vector_iterator<std::_Vector_val<std::_Simple_types<_Ty>>> &"

And in the code the first "vec" in the loop is marked red.

Without using reference the code runs fine on all platforms.
But I want to use reference because the code is in a performance critical part of my application.

So why does the code run fine as Visual Studio C++ console application and doesn't compile in Qt? What's wrong?

Regards,
mireiner

CKurdu

Hi
Do you have "CONFIG += c++11" in your pro file?

jsulm

@mireiner Remove & after auto. begin() returns an iterator and not a reference to an iterator.

mireiner

Yes I got
CONFIG += console c++11
and tried also
CONFIG += console c++1z
and
QMAKE_CXXFLAGS += -std:c++latest
all with no luck :-(

jsulm

@CKurdu As far as I know this is not needed with Microsoft compiler.

mireiner

@jsulm

Sorry I mainly used ranged based loops and not very often iterators. So let me ask again to make sure:

You mean: Reference can't be used here?
Is there any way to use iterators with reference at all? How does the code look like then?

aha_1980

@mireiner an iterator is a reference (or a pointer, to be more specific)...