Question

code snippet:

// some code
SDL_Surface* t = Display->render_text(text);
int z=100;
Display->blit_image(t,z,100);
// some more code

does not compile because z magically changes to an int&,
file.cpp:48: error: no matching function for call to ‘display::blit_image(SDL_Surface*&, int&, int)

how can this happen?

post scriptum:
the following works if i put them in place of Display->blit_image(t,z,100)

Display->blit_image(t,z,100,0);

but i am sure that th 4th param is optional because the exact same function works elsewhere without it

pps: i created a minimal-case of my code that behaves as describd above
it’s 3 files:

monkeycard.cpp: http://pastebin.com/pqVg2yDi

display.hpp: http://pastebin.com/xPKgWWbW

display.cpp: http://pastebin.com/nEfFX1wj

g++ -c display.cpp monkeycard.cpp fails with:
monkeycard.cpp: In member function ‘void monkeycard::messagebox(std::string)’:
monkeycard.cpp:28: error: no matching function for call to ‘display::blit_image(SDL_Surface*&, int&, int)’
display.hpp:26: note: candidates are: void display::blit_image(SDL_Surface*, int, int, SDL_Rect*)

Answer 1

Having seen the code, the defaults should be given in the header and not in the implementation file.

When you are compiling “monkeycard.cpp”, the compiler has only the information in the headers to work with. The compiler has no idea that blit_image has default arguments, and therefore cannot match the function to call.