std::make_pair

Hello,

I'm using std::make_pair, to fill a std::pair. I only get some error and I can't find out why.

Code:

---

std::pair <LONG,LONG> ControlSize;
ControlSize = std::make_pair(rc.right - rc.left,rc.bottom - rc.top);

---

error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const std::pair<_Ty1,_Ty2>' (or there is no acceptable conversion)

Grz

this compiles

Code:

---

#include <utility>
#include <Windows.h>

int main()
{
    RECT rc = {0};
    std::pair <LONG,LONG> ControlSize;
    ControlSize = std::make_pair(rc.right - rc.left,rc.bottom - rc.top);
    return 0;
}

---

this does not

Code:

---

#include <utility>
#include <Windows.h>

int main()
{
    RECT rc = {0};
    const std::pair <LONG,LONG> ControlSize;
    ControlSize = std::make_pair(rc.right - rc.left,rc.bottom - rc.top);
    return 0;
}

---

Quote:

---

error C2678: binary '=' : no operator found which takes a left-hand operand of type 'const std::pair<_Ty1,_Ty2>' (or there is no acceptable conversion)

---

Notice the const. Once the ControlSize has been initialized, there is no changing it without breaking const, but you can initialize it with make_pair like

Code:

---

#include <utility>
#include <Windows.h>

int main()
{
    RECT rc = {0};
    const std::pair <LONG,LONG> ControlSize = std::make_pair(rc.right - rc.left,rc.bottom - rc.top);
    return 0;
}

---

I never use const infront of it. I use it as the first example and it doesn NOT work. That's what is so weird, or there is a reason I don't know yet.

Quote:

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Originally Posted by NLscotty

I never use const infront of it. I use it as the first example and it doesn NOT work. That's what is so weird, or there is a reason I don't know yet.

---

If you get a compiler error, you should post a minimal, but complete code example. Your example is incomplete -- it's just two lines copied from some function.

You should also post the compiler your using, maker and version.

Here is a complete example that compiles successfully:

Code:

---

#include <map>

int main()
{
    std::pair <long, long> ControlSize;
    ControlSize = std::make_pair(0, 0);
}

---

This was compiled using the online Comeau C++ compiler. There are no errors in this code.

Regards,

Paul McKenzie

Oki, ill post some more code

Code:

---

class WinTraits
{
public:
        WinTraits();
//,,,,,,,,,,,,,,,
//,,,,,,,,,,,,,,,

private:

std::pair <LONG,LONG> ControlSize;
//...............
//................
};

WinTraits::WinTraits()
        :        //.................
                ControlSize(0,0)
{
//..........
}

std::pair<LONG,LONG> WinTraits::GetSize() const
{
        if(!hwnd)
                return ControlSize;
       
        RECT rc = {0};
        ::GetWindowRect(hwnd, &rc);
        ControlSize =  std::make_pair<LONG,LONG>(rc.right - rc.left,rc.bottom - rc.top);
        return ControlSize
}

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That's all the code with 'ControlSize'. Hope this helps.

Code:

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std::pair<LONG,LONG> WinTraits::GetSize() const

---

you have choosen not to modify any class member by placing that const in red, but you have just modified one.

Quote:

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Originally Posted by SkyNetTo

Code:

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std::pair<LONG,LONG> WinTraits::GetSize() const

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you have choosen not to modify any class member by placing that const in red, but you have just modified one.

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Omg, so stupid. Thanks a lot :)