4

I have this problem

83:24: error: non-const lvalue reference to type 'QImage' cannot bind to a temporary of type 'QImage' cameraimplementation.h:23:34: note: passing argument to parameter 'nextImage' here

caused by this code

updateImageData(toQImage());

with 

void updateImageData(QImage& nextImage); QImage toQImage();

How can I solve this other than including a temporary variable.

QImage image = toQImage(); updateImageData(image);
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4
  • 4
    why would you want to write updateImageData(toQImage()); ? It updates an image that will be gone on the next line Commented Aug 31, 2018 at 12:55
  • 2
    What are you trying to achieve? Construct a temporary image, update it, and then discard it? C++ doesn't let you, because such a thing has a substantial chance of being a mistake. Commented Aug 31, 2018 at 12:55
  • in a world where you have millions of possibilities to shoot yourself in the foot it can be confusing when you find one way that is not allowed :P Commented Aug 31, 2018 at 12:56
  • The image in the class is updated by the passed one, not the image passed to the function. Mabye saveImageData would be better? Commented Aug 31, 2018 at 20:15

1 Answer 1

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4

You can't.

The C++ standard does not allow the binding of an anonymous temporary to a reference, although some compilers allow it as an extension. (Binding to a const reference is allowed.)

Aside from the workaround you already have, if you can change the function to take const QImage& then that would be better.

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1 Comment

It works. updateImageData creates a copy of the QImage. It is thus valid to pass it as const.

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