I'm using g++ compiler, and I want certain lines of my c++ code to be commented out or not commented, depending on my config.
I realise that I could do:
#ifdef DEBUG
cout << "foo" << endl;
#endif
But I would rather it all be on a single line:
#define DEBUG //
DEBUG cout << "foo" << endl;
...with DEBUG being a macro for //. But writing #define DEBUG // yields nothing. Can anyone tell me what to do?
But I would rather it all be on a single line:
#define DEBUG //
People have given good examples of how to accomplish what you want, but no one has commented on why your approach didn't work.
Your approach will never work. It can't work. There is no mechanism for defining a macro that becomes a start of comment sequence for the simple reason that comments don't exist by the time preprocessor symbols are defined. They have already been stripped out.
Here's one way of doing it:
#ifdef DEBUG
#define DEBUG_LOG(x) std::cout << x << std::endl;
#else
#define DEBUG_LOG(x)
#endif
DEBUG_LOG("foo")
DEBUG_LOG( "variable=" << variable ); in this method, so using all you can use in coutOne trick from a Dr. Dobbs article:
#if _DEBUG
// dbgInC defined as "printf" or other custom debug function
#define dbgInC printf
// dbgInCpp defined as "cout" or other custom debug class
#define dbgInCpp cout
#else
// dbgInC defined as null [1]
#define dbgInC
// dbgInCpp defined as "if(0) cerr" or "if(1); else cerr"
#define dbgInCpp if(0) cerr
#endif
This has the advantage of allowing multi-line statements:
dbgInCpp << "Debug in C++: "
<< a // a is an integer
<< b /* b is char array */
<< c // c is a float
<< endl;
It is not idiomatic in C. Prefer use the usual form, e.g.:
#ifdef DEBUG
count << "foo" << endl;
#endif
Or (as assert) :
#ifndef NDEBUG
count << "foo" << endl;
#endif
For sake of readability. You can also encapsulate this code in a macro:
#ifdef DEBUG
#define PRINT_DEBUG(s) cout << s << endl
#else
#define PRINT_DEBUG(s) (void)0
#endif
You might have
#ifndef NDEBUG
#define DBGOUT(Out) cout << __FILE__ << ":" << __LINE__ << ":" \
<< Out << endl
#else
#define DBGOUT(Out) do {} while(0)
#endif
and use in your code things like
DBGOUT("x is " << x);
I use the NDEBUG symol, because <assert.h> and <cassert> use it.
