Re: Passed value not being received

From:
"Jim Langston" <tazmaster@rocketmail.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 19 Dec 2007 15:16:36 -0800
Message-ID:
<sDhaj.34$zc6.29@newsfe06.lga>
werasm wrote:

On Dec 19, 11:42 pm, Lilith <lil...@dcccd.edu> wrote:

On Thu, 20 Dec 2007 11:27:44 +1300, Ian Collins
<ian-n...@hotmail.com> wrote:

Lilith wrote:

I have a simple class method that receives as its second parameter
an unsigned int. But, regardless of what I do it never receives
the value that I pass to it. Instead it always comes up 4198769.
I've passed the number as a literal, as a variable and as a
constant and the method still recives the larger, unviable value.

I've tried changing the value I pass to it and I've tried casting a
constant and it still comes out wrong. I can't imagine a compler
(VS 2005) being broken enough to do this.

Any thoughts on this? 4198769 doesn't seem to be relevant to
anything.


Post a minimal example that demonstrates the problem. You will
probably fix the problem in the process of constructing the example
:)


Prototype within the class:
        void DrawBlock (point p, unsigned int size, sf::Color c);

Method:
void Roads::DrawBlock (point p, unsigned int size, sf::Color c)
   // size always shows up as 4198769
{
        int left = p.x - size/2;
        int, top = p.y - size/2;

        for (int i = top; i < top + size; i++) {
                for (int j = left; j < left + size; j++) {
                        canvas->SetPixel(j, i, c);
                }
        }

}

Call to the method:
.
.
const unsigned int siz = 5;
.
.
        fin.x = 80;
        fin.y = 20;

        Roadway.DrawBlock (fin, siz, Red);


I don't see an obvious problem. You are passing by value.
There are no implicit conversions (not that it would
matter). Perhaps try this minimal example:

#include <iostream>

void DrawBlock( unsigned size )
{
 std::cout << "size" << std::endl;
}

int main()
{
 const unsigned sz( 5 );
 DrawBlock( sz );
}

Then see what is printed. If the value is still as mentioned,
I suggest you change the name of the argument "size" to something
else, as it may be that it is macro expanded (the only other thing
I can think of).


If the value remains after you change the variable size, it may be a stack
overflow somewhere which can cause strange values as something is writing to
memory it shouln't. You should also put this in a debugger, look at the
value of siz before the call and trace into the call. Are you using arrays
or pointers in your program? If so, check where they are writing that they
aren't writing off the end of the buffer or before the buffer.

--
Jim Langston
tazmaster@rocketmail.com

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