Question

Pointer question: return makes pointer from integer without a cast

Asked by: Jasbir21

Hi,
I did a small code so that return type is of pointer..but I am getting error: return makes pointer from integer without a cast .

int *add(int *,int*);

int main()
{
 int *a=10, *b=50;
 int *c;

*c=add(&a,&b);
printf("The value is %d\n",*c);

return 1;

}

int *add(int *a,int *b)
{
return (*a + *b);

}

This Question has been solved and asker verified All Experts Exchange premium technology solutions are available to subscription members.

Subscribe now for full access to Experts Exchange and get

Instant Access to this Solution

  • Plus...
  • 30 Day FREE access, no risk, no obligation
  • Collaborate with the world's top tech experts
  • Unlimited access to our exclusive solution database
  • Never be left without tech help again

Subscribe Now

Asked On
2007-05-26 at 00:31:17ID22596112
Tags

integer

,

without

,

pointer

,

from

,

makes

Topic

C Programming Language

Participating Experts
1
Points
125
Comments
6

Trusted by hundreds of thousands everyday for fast, accurate and reliable tech support.

  • "The time we save is the biggest benefit of Experts Exchange to Warner Bros. What could take multiple guys 2 hours or more each to find is accessed in around 15 minutes on Experts Exchange." Mike Kapnisakis, Warner Bros.
  • "Our team likes having a resource that is more secure than just using Google and most experts using this service really know their stuff. It's nice to look here first versus using Google." Dayna Sellner, Lockheed Martin
  • "Anytime that I've been stumped with a problem, 9 out of 10 times Experts Exchange has either the accepted solution or an open discussion of the potential solution to the problem." Kenny Red, eBay Inc.

See what Experts Exchange can do for you.

Got a question?

We've got the answer.

Experts Exchange has been collecting answers to technology questions since 1996…3 million and counting! If you have a question, chances are we already have your answer.

Screenshot of Experts Exchange Knowledgebase

Need individual assistance?

Our experts are ready to help.

If you can't find the exact answer you're looking for, ask our exclusive community of 50,000 experts. You’ll get a personalized answer from a trusted professional.

Screenshot of Experts Exchange Knowledgebase

Want to learn from the best?

Read articles from industry experts.

Thousands of free tech tips, tricks, how-to’s and tutorials are available in our peer reviewed articles section. See for yourself how smart our experts are, no login required.

Screenshot of an Article

Working on a long term project?

Store your work and research.

Save solutions to your questions, answers you’ve discovered through searching plus helpful articles in your personal knowledgebase for easy future access.

Screenshot of Experts Exchange Knowledgebase

Access the answers to your technology questions today.

Subscribe Now

30-day free trial. Register in 60 seconds.

What Makes Experts Exchange Unique?

Members of the expert community talk about why the experience at Experts Exchange is different than what you will find anywhere else.

Trusted by the world's most respected brands.

image of each brand's logo

Faithfully serving IT professionals since 1996.

Experts Exchange Logo

Try it out and discover for yourself.

Subscribe Now

30-day free trial. Register in 60 seconds.

Related Solutions

  1. (int) Integer Cast
    How do I cast to an integer in JavaScript ? var i; .. ii = (int) i*0.5 .. I don't want it to be a float, but an integer, how is that done ??
  2. casting a pointer to unsigned int
    I came across something like the foll: packet_initialize ( (PACKET_HANDLE )p_pkt); where typedef UINT PACKET_HANDLE; and struct packet *p_pkt; I wonder how a pointer to packet can be cast to an unsigned int
  3. cast null to integer
    I get a integer valuea from SQL Sever stored procedure OUTPUT parameter. The value is casted into integer and pass to a variable. The problem is the value in the database can be null. How should I handle it? var1 = (int) parameterInteger1.Value
  4. Error: Integer from pointer without a cast.
    Hello Experts, I have the following error: packetgen.c: In function `sendpack': packetgen.c:96: warning: passing arg 1 of `create_tcp' makes integer from pointer without a cast packetgen.c:96: warning: passing arg 2 of `create_tcp' makes integer from pointer without a cast ...

Free Tech Articles

  1. WARNING: 5 Reasons why you should NEVER fix a computer for free.
    It is in our nature to love the puzzle. We are obsessed. The lot of us. We love puzzles. We love the challenge. We thrive on finding the answer. We hate disarray. It bothers us deep in our soul. W...
  2. SCCM OSD Basic troubleshooting
    SCCM 2007 OSD is a fantastic way to deploy operating systems, however, like most things SCCM issues can sometimes be difficult to resolve due to the sheer volume of logs to sift through and the dispe...
  3. Migrate Small Business Server 2003 to Exchange 2010 and Windows 2008 R2
    This guide is intended to provide step by step instructions on how to migrate from Small Business Server 2003 to Windows 2008 R2 with Exchange 2010. For this migration to work you will need the fo...
  4. Create a Win7 Gadget
    This article shows you how to create a simple "Gadget" -- a sort of mini-application supported by Windows 7 and Vista. Gadgets can be dropped anywhere on the desktop to provide instant information, ...
  5. Outlook continually prompting for username and password
    There have been a lot of questions recently regarding Outlook prompting for a username and password whilst using Exchange 2007. There are a few reasons why this would happen and I will try to cover t...
  6. Backup Exchange 2010 Information Store using Windows Backup
    There seems to be quite a lot of confusion around the ability to backup Exchange 2010 using the built in Windows Backup feature. This stems from the omission of this feature prior to Exchange 2007 s...

Cloud Class Webinars

  1. Avoiding Bugs in Microsoft Access
    Alison Balter takes and in-depth look at avoiding bugs in Access. In this webinar you will learn about using the immediate window to debug your applications, invoking the debugger, using breakpoints to troubleshoot, stepping through code, setting the next statement to execute, ...
  2. Top 10 Best New Features in Visio 2010
    Scott Helmers gives live demonstrations of the top 10 new features in Visio 2010. This webinar will teach you how to create compelling diagrams by adding shapes to the page with a single click, linking the shapes in a diagram to data in Excel (or SQL Server, or SharePoint), ...
  3. IT Consultant Business Secrets Revealed
    Michael Munger, Experts Exchange tech pro and IT consultant, pulls back the curtain on his very successful businesses and answers question on every IT consultant and business owner should know about. He shares secrets on what he did to solve the 5 most common problems in IT, ...
  4. Disaster Recovery and Business Continuity
    Quest CTO, Mike Billon, gives an overview of the steps involved in building a dunamic disaster recovery plan. Through case studies and an examination of software/hardware tooles for monitoring and testing, you'll gain a better understandin of where you are, where you want ...
  5. Organize Your Visio Diagrams with Containers and Lists
    Scott Helmers uses cross functional flowcharts, wireframe diagrams, data graphic legends and seating charts to teach you: how to ustilize all three new structured diagram components in Visio 2010, the best practices for organizeing shapes in previous version of Visio, how to organize ...
  6. How to Us Objects, Properties, Events and Methods in Microsoft Access
    Alison Dalter gives an in-depbth look at objects, properties, events and methods in Microsoft Access. In this webinar you will learn about using the object browser, referring to objects, working with properties and methods, working with object variables, understanding the ...

Join the Community

Give a Little. Get a Lot.

Join the community of experts here and help other tech pros by answering question in your area of expertise. You can earn FREE access to all Experts Exchange's premium features and resources.

Join the Community

Answers

 

by: Infinity08Posted on 2007-05-26 at 01:53:27ID: 19161422

*a is an int, and so is *b (you are dereferencing the pointers). So, doing this :

      *a + *b

has an int as result, NOT a pointer. So, your add function returns an int while it should return an int*.

Now, that's not the only problem in your code :

        int *a = 10;

a is an int*, and you assign it a value. That will more than likely generate a runtime error. Here's some corrected code :

      int add(int*, int*);           /* <--- the function takes two int pointers as argument, and returns the sum as an int */

      int main() {
          int a = 10, b = 50;       /* <--- we make a and b proper ints */
          int c = 0;                      /* <--- this will be the result of the function */

          c = add(&a, &b);          /* <--- instead of passing the values of a and b, we pass their addresses */

          printf("The value is %d\n", c);

          return 0;                      /* <--- usually, 0 indicates correct termination of the program - non-zero values indicate an error */
      }

      int add(int *pa, int *pb) {
          return (*pa + *pb);     /* <--- we dereference the pointers to get the actual values, sum them and return the result */
      }

 

by: Infinity08Posted on 2007-05-26 at 02:04:09ID: 19161442

If you want to return a pointer from a function, you need to make sure that it points to valid memory.

Here are two ways you can make sure of that :

1) by allocating memory outside of the function, and passing it as an argument :

        int *add(int *psum, int *pa, int *pb) {
            *psum = *pa + *pb;
            return psum;
        }

     and you can call it like this :

        int a = 10, b = 50;
        int sum = 0;
        int *psum = 0;

        psum = add(&sum, &a, &b);

        printf("  sum : %d\n  sum via pointer : %d\n", sum, *psum);

     note that sum will contain the result of the function, and psum will point to that SAME value. In other words, if after calling the function, we change sum :

        sum = 20;

        printf("  sum : %d\n  sum via pointer : %d\n", sum, *psum);

     then psum will also point to 20.


2) by allocating memory inside of the function :

        int *add(int *pa, int *pb) {
            int *psum = (int*) calloc(1, sizeof(int));
            *psum = *pa + *pb;
            return psum;
        }

     The calloc call allocates memory dynamically for the return value. This memory will still be valid after the function returns, which is what we need.

     and you can call it like this :

        int a = 10, b = 50;
        int *psum = 0;

        psum = add(&a, &b);

        printf("  sum via pointer : %d\n", *psum);

        free(psum);

     note that psum will point to the result of the addition.

     The call to free is ABSOLUTELY needed once we don't need the result any more ... otherwise there is a memory leak.

 

by: Jasbir21Posted on 2007-05-26 at 03:10:19ID: 19161546

Hi ,

Thanks a lot .
Can i assume that a pointer needs   to point to something, so it is illegal to asssign it to a variable.
We could assign it to a variable only if we allocate the memory properly using malloc, calloc...

 

by: Infinity08Posted on 2007-05-26 at 03:47:04ID: 19161585

>> Can i assume that a pointer needs   to point to something

A pointer can point to nothing, but in that case it's illegal to dereference it. For example :

      int *ptr = 0;    /* <--- this pointer points to nothing */
      int a = *ptr;   /* <--- this is illegal, and will generate a runtime error */

In the above, you're trying to dereference a pointer that points to nothing. In other words : you're trying to get a value that is not there - that's illegal.

However, if the pointer points to something, like this :

      int a = 10;
      int *ptr = &a;     /* <--- we make the pointer point to the value a */
      int b = *ptr;       /* <--- this is OK : b will now have the same value as a */

then it's OK.

Similarly, we can do this :

      int *ptr = (int*) calloc(1, sizeof(int)); /* <--- we make the pointer point to a valid memory location */
      *ptr = 20;    /* <--- this is OK : we can dereference the pointer, and place a value in the memory it points to */
      free(ptr);     /* <--- once we don't need that value any more, we free it */
      int a = *ptr;     /* <--- this is now illegal. We just cleaned up ptr, so it doesn't point to valid memory any more */



And, now with some drawings that might make things a bit clearer.

1) this line :

      int *ptr = 0;

    has this as result :

        ptr -->

    ie. ptr points to nothing

2) this line :

      int *ptr = (int*) calloc(1, sizeof(int));

    makes ptr point to an empty memory block :

                   ----------
        ptr --> |          |
                   ----------

    this memory block might contain any value (we don't know which), so we give it a value :

      *ptr = 20;

    which has this as result :

                   ----------
        ptr --> |   20   |
                   ----------

3) this line :

      int a = 10;

    has this as result :

                   ----------
                   |   10   |
                   ----------

    ie. there's an int somewhere in memory with the value 10.

    When we do this :

      int *ptr = &a;

    we let ptr point to that int :

                   ----------
        ptr --> |   10   |
                   ----------

    so, if we do this :

      *ptr = 20;

    then we change the value of a :

                   ----------
        ptr --> |   20   |
                   ----------


Does that make things a bit clearer ?

 

by: Jasbir21Posted on 2007-05-26 at 04:14:56ID: 19161631

Much clearer . Thank you very much..
I spent half day ..thinking what could go wrong . Thanks again....
I am going to post another question on pointers as well....Please look at it ...

 

by: Infinity08Posted on 2007-05-26 at 04:16:02ID: 19161634

No problem :)

20120131-EE-VQP-002

3 Ways to Join

30-Day Free Trial

The Experts

98% positive feedback on 31,087 answers since March 2000. angeliii is a Microsoft Most Valuable Professional for his work with MS SQL Server & Develoment.

He has also proven his knowledge of Visual Basic Programming, PHP Scripting and Oracle Databases.

The Experts

97% positive feedback on 10,752 answers since July 2000. lrmoore has more than 18 years experience in the networking industry.

The six-time Mircosoft MVPs specialties include firewalls, virtual private networking, and network management.

Testimonials

"...and excellent source for support... Kind of like having your very own IT dept." Electriciansnet

Testimonials

"I was apprehensive at signing up at first. However... it has already made my life as an IT administrator much easier." JaCrews

Testimonials

"WOW! You guys have great, active, and knowledgeable people on here." moore50

Business Clients

Business Clients

In the Press

"If you’ve got a question... Experts Exchange can supply an answer.”

In the Press

"...an invaluable aid for both IT professionals and those who require tech support."

In the Press

"where IT professionals provide quick answers on just about any topic"

Business Account Plans

Loading Advertisement...