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copied!<p>The error message tells you what you're trying to pass. With automatic conversions and whatnot, that doesn't mean the function must have exactly that signature.</p> <p><code>int&</code> here just means that the parameter you've provided is an lvalue, and so it <em>could</em> be passed as a non-const reference. A function can match with that parameter as an <code>int&</code>, <code>const int&</code>, <code>int</code>, <code>long</code>, <code>const float&</code>, etc.</p> <blockquote> <p>the point is that if instead of z i write 100 it works.</p> </blockquote> <p>That's interesting. I can't immediately think of a way to write a function that accepts an integer literal, but not an integer variable. The following code compiles, of course:</p> <pre><code>struct SDL_Surface; struct SDL_Rect; struct display { void foo(SDL_Surface* img, int x=0, int y=0, SDL_Rect* clip=0) {} }; int main() { display d; int z = 0; SDL_Surface *p = 0; d.foo(p,z,100); } </code></pre> <p>So there must be something else you haven't mentioned yet, which causes the issue.</p> <p>Edit: visitor and Charles Bailey (in a comment) have the answer. The defaults are missing from your declaration of the function, so as far as the compiler is concerned you are trying to call a 4-parameter function with 3 arguments. The <code>&</code> is not the problem.</p> <p>For future reference: when James McNellis asked you for "the" declaration of your function, he meant the declaration which is visible in the translation unit making the call. In your pastebin code, the <em>definition</em> is not visible in that translation unit, and the compiler cannot reach in to a completely different .cpp file and realise that the function is supposed to have parameter defaults. In C++, default values are set up in the calling code, for reasons to do with how calling conventions work.</p>

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