[R] error() and C++ destructors

[Lennart.Borgman@astrazeneca.com]

And maybe I stressed Erik a bit, because he corrected himself some minutes
later (when I was no longer looking over his shoulder). Again on behalf of
Erik.

- Lennart


-----Original Message-----
From: Källen, Erik 
Sent: 9 mars 2004 13:40
To: Borgman, Lennart
Subject: RE: [R] error() and C++ destructors


Whoops.

This code leaks memory for the exception.
It would be better to throw a pointer:

void my_error(const string &str) {
	throw new error_exception(str);
}

int my_method(int a, char *b) {
	try {
		return real_my_method(a, b);
	}
	catch (error_exception *pe) {
		static char error_msg[SOME_LARGE_NUMBER];
		strncpy(error_msg, pe->msg.c_str(), sizeof(error_msg));
		delete pe;
		error(error_msg);
	}
}

-----Original Message-----
From: Borgman, Lennart 
Sent: 9 mars 2004 13:35
To: 'r-help at stat.math.ethz.ch'
Subject: RE: [R] error() and C++ destructors


I am sending this reply on behalf of Erik (who is not a member of this
list).

- Lennart


-----Original Message-----
From: Källen, Erik 
Sent: 9 mars 2004 11:37
To: Borgman, Lennart
Subject: RE: [R] error() and C++ destructors


I would do something like:

class error_exception {
public:
	error_exception(const string &str) : msg(str) {}
	string msg;
};

void my_error(const string &str) {
	throw error_exception(str);
}

int real_my_method(int a, char *b) {
	/*
	some code...
	*/
	return 0;
}

// this is the public method:
int my_method(int a, char *b) {
	try {
		return real_my_method(a, b);
	}
	catch (error_exception &e) {
		error(e.msg);
	}
}

You could probably even create a macro like:
#define R_METHOD_IMPL(rettype, name, paramlist) \
rettype real_##name paramlist; \
rettype name paramlist { \
	try { \
		return real_##name paramlist; \
	} \
	catch (error_exception &e) { \
		error(e.msg); \
	} \
} \
rettype real_##name paramlist


You would use this macro like:
R_METHOD_IMPL(int, my_method, (int a, char *b)) {
	// source code here
}

I think it would work, but I'm not sure (untested).


/Erik Källén


-----Original Message-----
From: Vadim Ogranovich [mailto:vograno at evafunds.com]
Sent: 2 mars 2004 22:00
To: R Help List
Subject: [R] error() and C++ destructors


Hi,
 
I am writing C++ functions that are to be called via .Call() interface.
I'd been using error() (from R.h) to return to R if there is an error,
but then I realized that this might be not safe as supposedly error()
doesn't throw an exception and therefore some destructors do not get
called and some memory may leak. Here is a simple example
 
extern "C" void foo() {
    string str = "hello";
    error("message");
}
 
The memory allocated for str is leaked.
 
Did anyone think about this and find a way to work around the problem?
 
Thanks,
Vadim

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