g++: class size or file size limitations: NONTRIVIAL BUG

[Neil Zanella]

Hello,

I have a file with about 1400 lines of C++ code most of which
consists of a single class. An oversimplified version of the
file is the following...

--- BEGIN ORIGINAL FILE ---

#include <iostream>

class Foo {
public:
Foo(int x): _x(x) { init(); }
private:
void init();
int _x;
};

void Foo::init() {
std::cout << "Hello, World!" << std::endl;
}

int main(void) {
Foo foo(1024);
}

--- END ORIGINAL FILE ---

I then make the following change to the file, and would expect the
output to be the same, but alas, what I see is that the code compiles
with no errors, even runs, but when it runs I get unexpected run time
errors that seem to depend on the amount of methods I add to the class
(i.e. if I add one more the whole things starts to malfunction). So
here is what I think should be equivalent, but g++ produces an
executable file that does NOT do the same thing:

--- BEGIN MODIFIED EXAMPLE ---

#include <iostream>

class Foo {
public:
Foo(int x): _x(x) { init(); }
private:
void initialize();
void init();
int _x;
};

void Foo::initialize() {
init();
}

void Foo::init() {
std::cout << "Hello, World!" << std::endl;
}

int main(void) {
Foo foo(1024);
}

--- END MODIFIED EXAMPLE ---

Now this is a trivial modification. On this small code snippet,
everything works fine, but on my 1400 line class it's not the case,
and I am using GNU g++ 3.2.2 on a Debian Linux box.

So, can anyone please provide a hint as to what the problem may be???

This must be the most obscure bug I've ever come across.

Thanks,

Neil

 

[David B. Held]

[...]
Now this is a trivial modification. On this small code snippet,
everything works fine, but on my 1400 line class it's not the
case, and I am using GNU g++ 3.2.2 on a Debian Linux box.

So, can anyone please provide a hint as to what the problem
may be???

Incorrect assumptions about the failure mode? ;>

This must be the most obscure bug I've ever come across.

Perhaps the bug is not in the compiler, but in the source. ;>
Without seeing your code, it is impossible to determine
which. If you really think it is a compiler bug, you should
post your code to the gcc bug list or GNATS.

Dave

 

[Frank Schmitt]

Hello,

I have a file with about 1400 lines of C++ code most of which
consists of a single class. An oversimplified version of the
file is the following...

Now this is a trivial modification. On this small code snippet,
everything works fine, but on my 1400 line class it's not the case,
and I am using GNU g++ 3.2.2 on a Debian Linux box.

So, can anyone please provide a hint as to what the problem may be???

I bet you are overwriting memory you aren't supposed to - e.g.
stepping over the bounds of an array or sth like that.
Without the real source code, it's impossible to tell - you are
in for a really exciting debugging session
You might want to check out efence or valgrind - useful tools to
find / prevent this kind of programming error.

HTH & kind regards
frank

 

[tom_usenet]

Now this is a trivial modification. On this small code snippet,
everything works fine, but on my 1400 line class it's not the case,

1400 lines is a bit long for a class. They shouldn't normally be
longer than a few hundred lines. You should probably split the
responsibilities of your class between several smaller ones.

and I am using GNU g++ 3.2.2 on a Debian Linux box.

So, can anyone please provide a hint as to what the problem may be???

This must be the most obscure bug I've ever come across.

The problem will likely be an obscure bug - an uninitialized variable,
out of bounds array access, double deletion of a pointer or other
undefined behaviour. The only way to find it is careful use of a
debugger. The bug might be in code from a completely different class,
or it might be how you are using another class.

There is a vague possibility that it might be a compiler bug, but this
is orders of magnitude less likely than it being a "simple" bug in
your code.

Tom

 

[Gianni Mariani]

Neil Zanella wrote:
....
-

Now this is a trivial modification. On this small code snippet,
everything works fine, but on my 1400 line class it's not the case,
and I am using GNU g++ 3.2.2 on a Debian Linux box.

So, can anyone please provide a hint as to what the problem may be???

This must be the most obscure bug I've ever come across.

try running your code under valgrind (preferred) or efence and see what
it says.