Solved

array of structs problem - HELP

Posted on 1998-12-18
5
299 Views
Last Modified: 2013-12-14
Can somebody tell me how to actually get this to work ??

 I have a DLL that returns a pointer to an array of structs (I think);
 I dont have a Lib file so I have had to load it explicitly (works fine).

 // header snippet
 
 typedef struct
 {
 int i;
 char c[20];
 } X_Y;

 typedef X_Y  *X_Y;

 // DLL prototype
 typedef BOOL (WINAPI *LPGETLIST) (int iCount,  X_Y **ppUsers);
 // Documentation for the DLL function.
 // In args none.
 // Out, returns ..  iCount the number of users.
 // ppUsers ..  a pointer to the users array.
 // The data returned is in the order of the user list, top to bottom
 // The users array is initialized with int i and char c.

 HINSTANCE hDLL;
 LPGETLIST lpGetList;
 X_Y *ppUsers;
 BOOL uReturnVal;
 int iCount, j;
 
 // main snippet

 hDLL = LoadLibrary("The.dll");
 // works fine

 lpGetList = (LPGETLIST) GetProcAddress(hDLL, "TheGetListFunc");
 uReturnVal = lpGetListDet (&iCount, &ppUsers);
 // works fine (uReturnVal TRUE)

// HOW do I access members of the pointed to structs
// I have tried this below DOES NOT WORK

 for(j = 0; j < iCount; j++) {
 printf("%d\n", ppUsers[j].i);      
 // print to screen      
 }

// Free user structures and the array itself.
0
Comment
Question by:cosmicmike
  • 3
5 Comments
 

Author Comment

by:cosmicmike
ID: 1255305
ignore this typo:
uReturnVal = lpGetListDet (&iCount, &ppUsers);
should be:
uReturnVal = lpGetList (&iCount, &ppUsers);

0
 
LVL 8

Expert Comment

by:Answers2000
ID: 1255306
printf( "%d\n", (*pUsers[j])->i )) ;

The trick is to read hungarian notation (on the front of variable names)

p = pointer to whatever, in your case a struct, therefore use -> to access a member
pp = pointer to pointer
The * dereferences a pointer, so *ppUsers is a pointer to a user struct


0
 

Author Comment

by:cosmicmike
ID: 1255307
Tried this
printf( "%d\n", (*ppUsers[j])->i );  

Ad get this compile error
error C2232: '->i' : left operand has 'struct' type, use '.'
0
 

Author Comment

by:cosmicmike
ID: 1255308
ppUsers is already a double pointer to a struct
0
 
LVL 1

Accepted Solution

by:
lafanga earned 100 total points
ID: 1255309
X_Y *ppUser; // means that *ppUser is a Structure and ppUser is a pointer to the structure

For 1 given structure:
retrieve values by *ppUser.i or ppUser->i

Now, &ppUser is a pointer, to the pointer of the structures
Say &ppUser  = pppUser

So Your first member,  that is a pointer to structure 1 will be pppUser[0] or &ppUser[0]
Now, this pointer (&ppUser[0]) will access data as (&ppUser[0])->i

So the net result should be:
printf("%d\n", (&ppUsers[j])->i);

0

Featured Post

PRTG Network Monitor: Intuitive Network Monitoring

Network Monitoring is essential to ensure that computer systems and network devices are running. Use PRTG to monitor LANs, servers, websites, applications and devices, bandwidth, virtual environments, remote systems, IoT, and many more. PRTG is easy to set up & use.

Question has a verified solution.

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

Suggested Solutions

Update (December 2011): Since this article was published, the things have changed for good for Android native developers. The Sequoyah Project (http://www.eclipse.org/sequoyah/) automates most of the tasks discussed in this article. You can even fin…
Examines three attack vectors, specifically, the different types of malware used in malicious attacks, web application attacks, and finally, network based attacks.  Concludes by examining the means of securing and protecting critical systems and inf…
The goal of this video is to provide viewers with basic examples to understand and use conditional statements in the C programming language.
THe viewer will learn how to use NetBeans IDE 8.0 for Windows to perform CRUD operations on a MySql database.

803 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