How can I define a macro (or a workaround for this) where the parameter is at the beginning of the line?
#define SINGLETON_IMPLEMENTATION(className) \
##className* ##className::instance_ = NULL;
This give a compiler warning (GCC 3.2.3): " '##' cannot appear at either end of a macro expansion"
You only need ## to append a parameter to another string. Your macro can be recast as
#define SINGLETON_IMPLEMENTATION(className) \
className* className::instance_ = NULL;
##
is the concatenation operator; the compiler is just complaining about that.
You cannot concatenate a token without something before it, ie at the beginning of the macro expansion; just try to remove the ##
at the beginning of the second line.
Also the second ##
seems wrong. If you just want to initialize a singleton pointer, remove both ##
s from your macro.
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