473,288 Members | 2,725 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,288 software developers and data experts.

what runs before main()? debug trouble

Hi!

First of all, I hope my problem is not too loosely tied to the
"standard C++" that is the topic of this group.

I have some code that exhibits a strange behaviour: on
one computer, where I compile with g++-3.2 it compiles and
works fine, on another computer, whether I compile with g++-3.0
or g++-2.95 (unfortunately 3.2 is not available) it crashes
with a segmentation violation on runtime.

I tried to find the offending code by commenting out most
of my program, and found out that the program crashes upon
entering an init() method of one of the objects. The bulk of
the function is never executed, since if I change its first line to
a std::cerr << "I'm here" << std::endl, it never appears on my
console.

Even if I try to execute this init() function as the first line of
main(), my program still crashes. As I can't use a debugger
on the system where it crashes, and it works fine on the
system where I have the debugger, I'm running out of options.

I've now come to the point, where if I start my main() with
a debug dump to cerr and then the offending function, I get
the debug dump at runtime, but not the debug dump of the
offending function. That leads me to the conclusion, that
something that runs before main is causing the trouble
(like overwriting memory, etc.). My question is...

/*** here's my C++ question ***/:

what is "the stuff" that runs before main()? I could recall
that top-level objects' constructors could be called
before main() and I double-checked these.
I also checked my statics and found nothing suspicious.
Is there anything else that runs any code before main
(apart from platform-specific stuff that goes before any
actual C++ code)?

Perhaps some of you can tell, by experience, what should
I look for? I've spent six hours now looking for the exact cause
and I'm getting frustrated. In plain-old-DOS I'd use a debugger
to single-step the code, unfortunately I can't do that now.
The assembler output of the compiler looks too complicated too.

TIA,
- J.

PS. The object whose method crashes my program is a child
object of a global object, like in

class B;

class A {
public:
B foo;
};

class B {
public:
init();
};

A global;

int main() {
global.foo.init(); // crashes
};

Of course this simple program works. That's why I'm lead to
believe there's some init stuff (not presented here, I can't post
the actual code because it's too long) that causes some hidden
trouble.
Jul 19 '05 #1
4 3814
Jacek Dziedzic wrote:

Of course this simple program works. That's why I'm lead to
believe there's some init stuff (not presented here, I can't post
the actual code because it's too long) that causes some hidden
trouble.


#include <cassert>

const int VALID = 98765;
const int DEAD = 0xdeaddead;

class validity {
int alive;
public:
validity() { alive = VALID; }
~validity() { alive = DEAD;}
bool valid(void * p);
};

bool validity::valid(void* p)
{
assert(p != 0);
return alive == VALID;
}

Stick something like the above cheapNcheerful in your
classes and add:

assert(vc.valid(this));

as the first statement of all methods. It will check that
things have been created, not delete, and provide some check
on memory getting trampled.

Jul 19 '05 #2
"lilburne" <li******@godzilla.net> wrote in message
news:bn*************@ID-203936.news.uni-berlin.de...
Jacek Dziedzic wrote:

Of course this simple program works. That's why I'm lead to
believe there's some init stuff (not presented here, I can't post
the actual code because it's too long) that causes some hidden
trouble.


#include <cassert>

const int VALID = 98765;
const int DEAD = 0xdeaddead;

class validity {
int alive;
public:
validity() { alive = VALID; }
~validity() { alive = DEAD;}
bool valid(void * p);
};

bool validity::valid(void* p)
{
assert(p != 0);
return alive == VALID;
}

Stick something like the above cheapNcheerful in your
classes and add:

assert(vc.valid(this));

as the first statement of all methods. It will check that
things have been created, not delete, and provide some check
on memory getting trampled.


Thanks for the advice, but I've now found out that my
problem is probably not C++ related. It looks like a
third party library (SCALI's mpi) is messing up my program.
When I cease to link it in, my program works fine. When
I link it, it core dumps. Must be some objects in the library
that have some code run before my main() that cause trouble,
damn it.

thanks, anyway
- J.
Jul 19 '05 #3
"Jacek Dziedzic" <ja***********@janowo.net> wrote in message
news:27**************@janowo.net...
[...]


Never mind my question. I've somehow figured out that
it's a third party library that causes the trouble. By some
weird magic everything works fine when I link it statically
and does not work when I link it dynamically. It still
puzzles me, but it's now definitely out of scope of this ng,
sorry.

- J.
Jul 19 '05 #4
Jacek Dziedzic wrote:
"Jacek Dziedzic" <ja***********@janowo.net> wrote in message
news:27**************@janowo.net...
[...]

Never mind my question. I've somehow figured out that
it's a third party library that causes the trouble. By some
weird magic everything works fine when I link it statically
and does not work when I link it dynamically. It still
puzzles me, but it's now definitely out of scope of this ng,
sorry.

- J.


Actually, there is a part that is within the scope of this
newsgroup. Many global and static variables are initialized
before the main() function. The constructor code for these
objects will be executed before the main() function.

Try this:
#include <iostream>
#include <cstdlib>

using std::cout;
using std::endl;

class My_Class
{
public:
My_Class()
{ cout << "My_Class constructor." << endl; }
~My_Class()
{ cout << "My_Class destructor." << endl;}
};

My_Class global_variable;

int main(void)
{
cout << "main() has begun." << endl;
cout << "main() has ended." << endl;
return EXIT_SUCCESS;
}

Hopefully, your compiler won't optimize the
"global_variable" away. If it does, make it
volatile:
volatile My_Class global_variable;

--
Thomas Matthews

C++ newsgroup welcome message:
http://www.slack.net/~shiva/welcome.txt
C++ Faq: http://www.parashift.com/c++-faq-lite
C Faq: http://www.eskimo.com/~scs/c-faq/top.html
alt.comp.lang.learn.c-c++ faq:
http://www.raos.demon.uk/acllc-c++/faq.html
Other sites:
http://www.josuttis.com -- C++ STL Library book
http://www.sgi.com/tech/stl -- Standard Template Library

Jul 19 '05 #5

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

2
by: hvaisane | last post by:
Valgrind says ==11604== Invalid read of size 4 ==11604== at 0x8048ABB: main (foo.cc:36) ==11604== Address 0x1B92415C is 4 bytes inside a block of size 8 free'd ==11604== at 0x1B90514F:...
10
by: linq936 | last post by:
Hi, I have many assert() call in my code, now I am considering to replace them with exception. The reason I want to do this change is that with the program going bigger and bigger, it is hard to...
6
by: Niklaus | last post by:
Hi, Can someone point out what is wrong with this code ? How can i make it better optimize it. When run it gives me seg fault in linux. But windows it works fine(runs for a long time). Do we...
28
by: Vishal Naidu | last post by:
i m new to the C world... i ve been told by my instructors not to use goto stmt.. but no one could give me a satisfactory answer as to why it is so.. plz help me out of this dilemma, coz i use...
10
by: Scott | last post by:
I have a simple asp.net app which works fine in debug mode, but crashes on the following line when I run it on the production server: Dim dt As DataTable I have tried the following variations...
3
by: Kceiw | last post by:
Dear all, When I use #include "queue.h", I can't link it. The error message follows: Linking... G:\Projects\Datastructure\Queue\Debug\main.o(.text+0x136): In function `main':...
15
by: robert maas, see http://tinyurl.com/uh3t | last post by:
Here's the source: #include <stdio.h> #include <errno.h> main () { char* str = "9999999999"; long long int llin; char* endptr; /* Set by strtoll */ int nch; errno = 0; llin = strtoll(str,...
8
by: Jothishankar | last post by:
Hi, I am new to c#. I am trying to build an application that does backup of files to an external hard disk. My application behaves strangely. When i run the application under debug mode (F5),...
2
by: Matthew Wilson | last post by:
In this code, I tried to kill my thread object by setting a variable on it to False. Inside the run method of my thread object, it checks a different variable. I've already rewritten this...
2
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 7 Feb 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:30 (7.30PM). In this month's session, the creator of the excellent VBE...
0
by: Aftab Ahmad | last post by:
Hello Experts! I have written a code in MS Access for a cmd called "WhatsApp Message" to open WhatsApp using that very code but the problem is that it gives a popup message everytime I clicked on...
0
by: Aftab Ahmad | last post by:
So, I have written a code for a cmd called "Send WhatsApp Message" to open and send WhatsApp messaage. The code is given below. Dim IE As Object Set IE =...
0
by: ryjfgjl | last post by:
ExcelToDatabase: batch import excel into database automatically...
0
by: marcoviolo | last post by:
Dear all, I would like to implement on my worksheet an vlookup dynamic , that consider a change of pivot excel via win32com, from an external excel (without open it) and save the new file into a...
1
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
0
by: jfyes | last post by:
As a hardware engineer, after seeing that CEIWEI recently released a new tool for Modbus RTU Over TCP/UDP filtering and monitoring, I actively went to its official website to take a look. It turned...
0
by: ArrayDB | last post by:
The error message I've encountered is; ERROR:root:Error generating model response: exception: access violation writing 0x0000000000005140, which seems to be indicative of an access violation...
1
by: PapaRatzi | last post by:
Hello, I am teaching myself MS Access forms design and Visual Basic. I've created a table to capture a list of Top 30 singles and forms to capture new entries. The final step is a form (unbound)...

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.