Null pointer (NULL array pointer is passed)

[aneuryzma]

Hi,

this is my code:

IplImage *image = 0;

....

if( !image ) {
image = cvCreateImage( cvGetSize(frame), 8, 3 );
image->origin = frame->origin;

}

myMethod(image);

cvShowImage( "CamShiftDemo", image );

....
Why do I receive this error ? I'm just passing the pointer image by
reference.. when myMethod finishes, I should have the same pointer to
the modified image instead it is NULL.. ?

[Eric Pruneau]

"aneuryzma" <pa**************@gmail.coma écrit dans le message de news:
6b**********************************...oglegroups.com...

Hi,

this is my code:

IplImage *image = 0;

...

if( !image ) {
image = cvCreateImage( cvGetSize(frame), 8, 3 );
image->origin = frame->origin;

}

myMethod(image);

cvShowImage( "CamShiftDemo", image );

...
Why do I receive this error ?

hummm what error again????

I'm just passing the pointer image by
reference.. when myMethod finishes, I should have the same pointer to
the modified image instead it is NULL.. ?

myMethod probably assign NULL to image... is myMethod declared like that

void myMethod(IplImage*& img);

If you do want to change the value of the pointer, but want to change the
value of what it is pointing to (I strongly suspect it is an image...) then
declare myMethod like that

void myMethod(IplImage* img);

Anyway, if after calling myMethod, your pointer is NULL, then you proibalby
have something else wrong in you method...
-----------------

Eric Pruneau

[Daniel T.]

aneuryzma <pa**************@gmail.comwrote:

this is my code:

IplImage *image = 0;

...

if( !image ) {
image = cvCreateImage( cvGetSize(frame), 8, 3 );
image->origin = frame->origin;

}

myMethod(image);

cvShowImage( "CamShiftDemo", image );

...
Why do I receive this error ? I'm just passing the pointer image by
reference.. when myMethod finishes, I should have the same pointer to
the modified image instead it is NULL.. ?

It took a bit, but I think I know what the problem is... Note:

void foo( int* i )
{
i = new int;
}

int main()
{
int* i = 0;
foo( i );
assert( i == 0 );
cout << "This is correct behavior.\n";
cout << "but it leaks memory.\n";
}

If the above doesn't demonstrate your problem, the please post more
code, what you gave us doesn't compile, much less run.

[Default User]

aneuryzma wrote:

Why do I receive this error ? I'm just passing the pointer image by
reference.. when myMethod finishes, I should have the same pointer to
the modified image instead it is NULL.. ?

Please post a complete, minimal program that demonstrates the problem.

Brian

[Jim Langston]

"aneuryzma" <pa**************@gmail.comwrote in message
news:6b**********************************@25g2000h sx.googlegroups.com...

Hi,

this is my code:

IplImage *image = 0;

...

if( !image ) {
image = cvCreateImage( cvGetSize(frame), 8, 3 );
image->origin = frame->origin;

}

myMethod(image);

cvShowImage( "CamShiftDemo", image );

Why do I receive this error ? I'm just passing the pointer image by
reference.. when myMethod finishes, I should have the same pointer to
the modified image instead it is NULL.. ?

You did not give us the signature of cvShowImage or what the error message
is. So without cod I can only guess.
Check line 42 of your program.