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User forums => Using Code::Blocks => Topic started by: r.stiltskin on March 27, 2015, 07:57:14 am

Title: preprocessor macro expansion
Post by: r.stiltskin on March 27, 2015, 07:57:14 am

Sorry if this is too dumb.

I can easily compile this code

Code

#include <iostream>
#define PROG_ID "dummy v" VER

using namespace std;

int main()
{
    cout << PROG_ID << endl;
    return 0;
}

in a makefile, or at the command line by running

Code

g++ -o dummy -DVER=\"0.1\" main.cpp

or

Code

export VAR=0.1
g++ -o dummy -DVER=\"$VAR\" main.cpp

but I can't work out how to do it in CB.

I tried putting
-DVER=\"0.1\"
in the project's build options/compilersettings/#defines

I also tried under Project/ build options/custom variables defining VER=0.1 and changing line 2 of the code to

Code

#define PROG_ID "dummy v" $VER

and various other combinations but nothing seems to work.

Title: Re: preprocessor macro expansion
Post by: oBFusCATed on March 27, 2015, 10:44:25 am

Don't prepend -D when you put something in the defines section.
Also you'll probably need to put more quotes until the string is passed correctly.
There are several levels of escaping that happens.

But if you don't need to pass real strings it is better to pass VER=1.0 and then in the code use a stringify like macro expansion to turn it to a string.
This way you won't depend on the expansions that happen in different build systems.

Title: Re: preprocessor macro expansion
Post by: r.stiltskin on March 27, 2015, 05:25:56 pm

Thanks. I see your point re stringify, but I'm bringing someone else's existing project into CB and trying to minimize the changes.

But your "several levels" comment gave the solution.  It turns out that I didn't need more quotes but needed more backslashes.  So putting
VER=\\"0.1\\"
in #defines did the trick.