Invalid Xcode transform when using objective-c ++
So if I run my program with the implementation as .m it works fine. Just changing it to .mm this line ...
CGContextRef myContext = [[NSGraphicsContext currentContext] graphicsPort];
to throw this error ...
error: invalid conversion from 'void*' to 'CGContext*'
Anyone have any ideas why just change this so it explodes or how to fix it?
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C ++ does not allow implicit type casting from void*
. In this case, implicit conversion from void*
(return type -[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 ++ operator static_cast
.
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C allows you to convert void * to an arbitrary type, C ++ doesn't. Once your file is .mm, it is compiled as C ++:
cristi:tmp diciu$ cat test.c
int main()
{
char * t = "test";
void * m = t;
char * g;
g=m;
}
cristi:tmp diciu$ g++ test.c
test.c: In function ‘int main()’:
test.c:7: error: invalid conversion from ‘void*’ to ‘char*’
cristi:tmp diciu$ gcc test.c
To fix, cast to the correct type, that is, explicitly pass "void *" to "CGContext *".
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