Bill’s Dev Blog

I found this interesting article on computerworld.com. Though I think this is a good overview of the diminishing IT skill scene, as Stewart Padveen says in the article, “Obsolescence is a relative — not absolute — term in the world of technology.”

I went several years programming in C/C++ without really knowing about these preprocessor variables. They can be very useful for debugging and logging of custom run time errors/warnings. I have not found a definitive list of them, but here is a list of some useful ones that I know of. (The following variables can vary by compiler, but generally work)

Instead of explaining these variables, here is an example program that demonstrates how you may use some of them:

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#include <iostream>
 
#define PUKE_TRACE(X,Y) puke_trace(__FUNCTION__, __FILE__, __LINE__, __threadid(), X, Y)
void puke_trace(const char* func, const char* file, int line,
				unsigned long thread, const char* msg, std::ostream& os)
{
	os << msg << " : Line " << line << ", file " << file
		<< ", function " << func << ", thread " << thread << ".\n";
}
 
int main(int argc, char* argv[])
{
	PUKE_TRACE("Test 1.",std::cout);
	PUKE_TRACE("Test 2.",std::cerr);
	PUKE_TRACE("Test 3.",std::clog);
	return 0;
}

The above program will output something like this:

__threadid() is not a preprocessor variable obviously, but it can be useful when tracing/debugging/logging multi-threaded applications, usually used in conjunction with preprocessor variables.

References:
http://www.codeguru.com/forum/showthread.php?t=231043
http://www.cppreference.com/preprocessor/preprocessor_vars.html