Question

So if I run my program with the implementation as .m it works fine. Just changing it to .mm causes this line…

CGContextRef myContext = [[NSGraphicsContext currentContext] graphicsPort];

to throw this error…

error: invalid conversion from 'void*' to 'CGContext*'

Anyone have any ideas why just changing that would make it blow up, or how to fix it?

Answer 1

C++ does not allow implicit type casting from void*. In this case, the implicit converstion from void* (the return type of -[NSGraphicsContext graphicsPort]) a CGContextRef is illegal. You can make the conversion explicit like this:

CGContextRef myContext = static_cast<CGContextRef>([[NSGraphicsContext currentContext] graphicsPort]);

See this SO question for a discussion of the C++ static_cast operator.