Solved

Dynamically allocate memory

Posted on 2016-09-02
9
56 Views
Last Modified: 2016-09-03
Hi Guys.

I'm not a C++ developer and with this project I'm doing I was forced to use C++. The problem is that when I run my app and try to open a service its says Access violation reading location 0x00000000. The pointer is
lphService

Open in new window

I've looked around on how to allocate memory but I don't seem to understand as to how could I assign this as the size will be returned by a function and I don't know the size by head. Any help?
0
Comment
Question by:MCSI Developers
  • 5
  • 4
9 Comments
 
LVL 31

Expert Comment

by:Zoppo
ID: 41781174
Hi MCSI Developers,

in general the error occurs in case a NULL-pointer is dereferenced, in your case the program tries to access (read) the value where the pointer lphService points to.

We need more info about this to help you, could you post some code (especially all parts where the lphService is instanced and used)?

Best regards,

ZOPPO
0
 
LVL 1

Author Comment

by:MCSI Developers
ID: 41781205
@ZOPPO, here is the code, and I get error -26.

    LPHSERVICE lphService;
    lphService = 0; // I put 0 because the EXIT_SUCCESS is also 0
    HRESULT hResult;
    WFSVERSION SvcVersion, SpiVersion;
    char szLogicalName[]="Epson1200";
    hResult = (WFSOpen(szLogicalName,WFS_DEFAULT_HAPP,"Epson Print",WFS_TRACE_NONE,TWO_MINUTES,RECOGNISED_VERSIONS,&SvcVersion,&SpiVersion,lphService));
    if(hResult == WFS_ERR_CANCELED)
    {
    cout << WFS_ERR_CANCELED << endl; // This returns -4
    }else if(hResult == WFS_ERR_SERVICE_NOT_FOUND)
    {
    cout << WFS_ERR_SERVICE_NOT_FOUND << endl; // This is -43
    }else if(hResult == WFS_ERR_CONNECTION_LOST)
    {
    cout << WFS_ERR_CONNECTION_LOST << endl; // -54
    }else if(hResult == WFS_ERR_INTERNAL_ERROR)
    {
    cout << WFS_ERR_INTERNAL_ERROR << endl; // -15
    }else if(hResult == WFS_ERR_INVALID_APP_HANDLE)
    {
    cout << WFS_ERR_INVALID_APP_HANDLE << endl; // -17
    }else if(hResult == WFS_ERR_INVALID_POINTER)
    {
    cout << WFS_ERR_INVALID_POINTER << endl; // This is the error I get which is -26
    }

Open in new window

0
 
LVL 31

Accepted Solution

by:
Zoppo earned 500 total points
ID: 41781716
ok, I guess the LPHSERVICE is a typedef to a HSERVICE pointer, so you should be able to solve it using one of these methods:

1. Use a pointer: change line 2 to
lphService = new HSERVICE;

Open in new window

and add this line after the last use of lphservice:
delete lphservice;

Open in new window


2. Use an instance: change line 1 to
HSERVICE hService;

Open in new window

delete line 2 and replace lphService by &hService in line 6.

In both cases the pointer passed to WSFOpen points to a valid instance, with 1. this instance is created in heap (and therefor has to be released after last use), with 2. the instance is put onto the stack, thus released automatically when the function terminates.

Hope this helps,

ZOPPO
0
 
LVL 31

Expert Comment

by:Zoppo
ID: 41781726
BTW, in addition two hints:

1. you don't need the ( and ) surrounding the WSFOpen call
2. using a chain of if/else to check a variable against constant values is not optimal for performance, in your case a switch/case statement would perform better.

ZOPPO
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 1

Author Closing Comment

by:MCSI Developers
ID: 41782249
Thanks thats really helped, now I get this error: WFS_ERR_SERVICE_NOT_FOUND. Is this because of missing device or the name is not found on the registry?
0
 
LVL 31

Expert Comment

by:Zoppo
ID: 41782922
Hm - sorry, that's hard to say for me since I don't know the API you're using - you could try if the program acts different when you dis- and re-connect the device, if so I would guess it's a problem with an unregistered (in registry) service.
0
 
LVL 1

Author Comment

by:MCSI Developers
ID: 41782924
I would guess it's a problem with an unregistered (in registry) service
do you mean my App is not registered or the device/service?
0
 
LVL 31

Expert Comment

by:Zoppo
ID: 41783110
I would guess the service is unregistered or it is registered but not running.
1
 
LVL 1

Author Comment

by:MCSI Developers
ID: 41783219
Thanks,
registered but not running
that does make seance.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

What is C++ STL?: STL stands for Standard Template Library and is a part of standard C++ libraries. It contains many useful data structures (containers) and algorithms, which can spare you a lot of the time. Today we will look at the STL Vector. …
Basic understanding on "OO- Object Orientation" is needed for designing a logical solution to solve a problem. Basic OOAD is a prerequisite for a coder to ensure that they follow the basic design of OO. This would help developers to understand the b…
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.
The viewer will learn additional member functions of the vector class. Specifically, the capacity and swap member functions will be introduced.

895 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now