Using #defines inside other #defines

[mastermike707]

#include <iostream>
#include <string>
#define NUM_CORES 2
#define COMMAND_STRING ("/bin/awesome -mt NUM_CORES -i "+fin+" -o "+fout).c_str()

using namespace std;

int main() {
	string fin = "fin here";
	string fout = "fout here";
	cout << COMMAND_STRING;
	return 0;
}

This outputs:
/bin/awesome -mt NUM_CORES -i fin here -o fout here
How can I get NUM_CORES to say 2 in the output string?

[Disch]

You probably shouldn't be using macros for this. A better solution would be to make a function:

#include <sstream>

//...

static const int num_cores = 2;

string command_string(const string& fin,const string& fout)
{
  stringstream s;
  s << "/bin/awesome -mt " << num_cores << " -i " << fin << " -o " << fout;
  return s.str();
}

int main()
{
  // ...
  cout << command_string( fin, fout );
}

[Mathhead200]

You can't interpolate a variable twice, yea perl/shell for teaching me this!

1 2 3

$yea = 'Perl'; $var = '$yea'; print "$var is Awesome!\n";

$yea is Awsome!

Okay... So basically the preprocessor macros only interpolate once.

[helios]

Technically, there's no reason why line 3 couldn't print "Perl is awesome!\n". I wrote a language once that did just that.

[Mathhead200]

Well with a simple edit:

1 2 3 4

$yea = 'Perl'; $var = "$yea"; print "$var is Awesome!\n"; #Did you find the difference? (It's not this comment)

Perl is Awesome!

However that defeats the purpose of this example.

helios wrote:

I wrote a language once that did just that.

Not that I'm trying to take away from the accomplishment, but why?

[helios]

Part of the language required me to allow something equivalent to this:
print $foo bar
So I decided to just solve a more general problem and make the part after the print a string and allow this:
bar="$foo $bar"
Avoiding infinite recursion was easy. Just store previous levels in a stack and check that no variable is traversed more than once in the same branch.