vector error, how to debug

[imutate]

I have an integer variable and I am testing it as follows

#define NULL_VAL -1
...
if (x[i].id != NULL_VAL)
{
std::cout << x[i].id << std::endl;
...
}

The output is
32767aborted

The index i=0 and this is being assigned to, so somewhere it is getting
overwritten.
x is defined as a vector over a template

Vec<sx;

struct s{
int id;
...
}

Is there a way I can trace back and see where this value is coming from
?

[Victor Bazarov]

im*****@hotmail .co.uk wrote:

I have an integer variable and I am testing it as follows

#define NULL_VAL -1
..
if (x[i].id != NULL_VAL)
{
std::cout << x[i].id << std::endl;
..
}

The output is
32767aborted

The index i=0 and this is being assigned to, so somewhere it is
getting overwritten.
x is defined as a vector over a template

Vec<sx;

This vector contains no elements. To add elements, use 'push_back'.

Read FAQ 5.8, while you're at it.

>
struct s{
int id;
..
}

Is there a way I can trace back and see where this value is coming
from ?

The error is on line 42 of your program.

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[Daniel T.]

In article <11************ **********@h48g 2000cwc.googleg roups.com>,
im*****@hotmail .co.uk wrote:

I have an integer variable and I am testing it as follows

#define NULL_VAL -1
..
if (x[i].id != NULL_VAL)
{
std::cout << x[i].id << std::endl;
..
}

Replace your code above with:

assert( i >= 0 && i < x.size() );
if ( x.at(i).id != NULL_VAL ) {
std::cout << x[i].id << std::endl;
}

What does it do then?

--
There are two things that simply cannot be doubted, logic and perception.
Doubt those, and you no longer*have anyone to discuss your doubts with,
nor any ability to discuss them.

[Kai-Uwe Bux]

im*****@hotmail .co.uk wrote:

I have an integer variable and I am testing it as follows

#define NULL_VAL -1
..
if (x[i].id != NULL_VAL)
{
std::cout << x[i].id << std::endl;
..
}

The output is
32767aborted

The index i=0 and this is being assigned to, so somewhere it is getting
overwritten.
x is defined as a vector over a template

Vec<sx;

struct s{
int id;
..
}

Is there a way I can trace back and see where this value is coming from?

The C++ language has no built feature for this. You can use a debugger: you
can then step through the program an watch the variable i. However,
debuggers are platform specific and specifics about particular debuggers
are therefore off-topic in this group. You may find better help in a forum
dedicated to your compiler or OS.
Best

Kai-Uwe Bux

[imutate]

Sorry, i is 0 and earlier in my code I set this to id to 0, I know this
because I'm printing it out there, so the only logical explanation is
that it is getting corrupted somewhere else. OK, if the dubugger is
off topic, I'll look elsewhere, thanks anyway.

[Daniel T.]

In article <11************ *********@m7g20 00cwm.googlegro ups.com>,
im*****@hotmail .co.uk wrote:

Sorry, i is 0 and earlier in my code I set this to id to 0, I know this
because I'm printing it out there, so the only logical explanation is
that it is getting corrupted somewhere else. OK, if the dubugger is
off topic, I'll look elsewhere, thanks anyway.

What does x.size() return?

--
There are two things that simply cannot be doubted, logic and perception.
Doubt those, and you no longer*have anyone to discuss your doubts with,
nor any ability to discuss them.

[imutate]

I am getting confused I should have pasted the actuall code. The
problem is the large vvalue is causing the abort none of the sizes goes
that high, I am looking to run a debugger to find where the index is
corrupted to this high value.

[Salt_Peter]

im*****@hotmail .co.uk wrote:

I have an integer variable and I am testing it as follows

#define NULL_VAL -1
..
if (x[i].id != NULL_VAL)
{
std::cout << x[i].id << std::endl;
..
}

The output is
32767aborted

The index i=0 and this is being assigned to, so somewhere it is getting
overwritten.

obviously, its being overwritten because its an index (or counter if
you prefer). That what indexes do.

x is defined as a vector over a template

no, x is a templated vector of type s elements.

>
Vec<sx;

struct s{
int id;
..
}

Is there a way I can trace back and see where this value is coming from
?

Why not show the code that is generating the (probably expected) output
you see?
32767 looks like the max numeric_limits for a short or 16 bit integer
on whatever platform/compiler you are running. Here is a test for you:

#include <iostream>
#include <ostream>
#include <limits>

int main()
{
int nlimit = std::numeric_li mits< int >::max();
std::cout << nlimit << std::endl;
}

What do you get?

[Mike Wahler]

<im*****@hotmai l.co.ukwrote in message
news:11******** ************@m7 3g2000cwd.googl egroups.com...

>I am getting confused I should have pasted the actuall code. The
problem is the large vvalue is causing the abort none of the sizes goes
that high, I am looking to run a debugger to find where the index is
corrupted to this high value.

I'm pretty sure Victor has identified your problem:

When you create a vector, *it is empty*, it contains
no elements. So any indexed access (e.g. [0]) will
produce undefined behavior (you're asking for the
value of something which does not exist.) First
put some elements in your vector, then you can
examine their values. But make sure the index you
use is at least one less than the value returned
by the vector's 'size()' member function (indices
start at zero).

And yes, the actual code is the only way we can
know for sure what's wrong.

-Mike

>

[Mike Wahler]

"Mike Wahler" <mk******@mkwah ler.netwrote in message
news:RO******** *********@newsr ead4.news.pas.e arthlink.net...

>
<im*****@hotmai l.co.ukwrote in message
news:11******** ************@m7 3g2000cwd.googl egroups.com...

>>I am getting confused I should have pasted the actuall code. The
problem is the large vvalue is causing the abort none of the sizes goes
that high, I am looking to run a debugger to find where the index is
corrupted to this high value.

I'm pretty sure Victor has identified your problem:

When you create a vector,

as in your example,

*it is empty*, it contains
no elements.

I needed to qualify my previous statement
because there are other ways to create a vector
which does contain elements (via contructors
other than default as you used).

-Mike