Unique identifiers

[SeventhStar]

Hey.
Is there a way to generate unique identifiers for a program. For example here's how it can be done with Visual C++ in a file.

#define UNIQ(s) s##__COUNTER__

then

int UNIQ(a) = 5; //a0
int UNIQ(a) = 6; //a1

etc...

Unfortunately the counter is restarted per file. Is there a way to make something global for the program.

Thanks in advance for any help.
(Visual C++ specific solutions are ok)

[Doron Moraz]

Is there a way to generate unique identifiers for a program?

You can use global object Mutexes to set a unique identifiers.
To create an identifier for a single process, simply pass a NULL to lpName.
You can create a mutex that refers to the same mutex in MORE than one process, by providing lpName.

HANDLE CreateMutex(LPSECURITY_ATTRIBUTES lpMutexAttributes,
BOOL bInitialOwner,
LPCWSTR lpName);

Consider the following code:

	HANDLE hMutex;
	hMutex=CreateMutex(NULL,true, NULL);
	if (hMutex==NULL)
	{
                 std::cout<<"Failed to create mutex";
                 return 0;
	}

	if (getLastError() == ERROR_ALREADY_EXISTS)
	{
		// ... Do Something ...
	}

EDIT: The code provided will only run for a single process, if you have more than one process that shares the same resource, you should provide the function a unique lpName.

Regards
Doron Moraz

[pm_kirkham]

Why do they need to be unique between files? - putting them into a no-name namespace or marking them static will prevent the linker treating them as the same.

[wildfrog]

Do you need the unique identifier at compile-time or at runtime?

At runtime you can create and use LUIDs (Locally Unique Identifiers) that are guaranteed to be unique across the OS (until you restart the system).

- petter

[Hermit]

int UNIQ(a) = 5; //a0
int UNIQ(a) = 6; //a1

This looks awful to me. How would it be useful?

1) The point of named variables is that you can (and should) give a meaningful name to a piece of data. If you have a group of related variables where it would make sense to give them all the same name, in addition to a unique number, guess what... that's an array. For example:

vector<int> a;
a.push_back(5);
a.push_back(6);

// or

int b[] = { 5, 6 /*,  etc */ };

// or, if you must

unsigned int counter = 0;
int c[SOME_SUFFICIENT_NUMBER];
c[counter++] = 5;
c[counter++] = 6;

2) Say you're debugging your code, and the variable a## looks suspicious. Where is this variable declared? Is it UNIQ(a), UNIQ(a), or UNIQ(a), or ...? Also, how do you refer to these variables in your code anyway?

[wildfrog]

This looks awful to me. How would it be useful?

Ahh. Now I realized what the question was all about. Hermit is correct. It's awful and never any reason for 'randomly' naming variables.

- petter