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Problem with nested structs

Posted on 2006-07-14
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Last Modified: 2010-04-24
Hi,

This is my first attempt to use Visual C++. I have code which compiles OK under Unix/Linux (using C) but not under Visual C++. Any ideas on the problem/solution?

#define WIN32_LEAN_AND_MEAN // Exclude rarely-used stuff from Windows headers
#include <windows.h>
#include <stdlib.h>
#include <stdio.h>
#include <float.h>
#include <math.h>
#include <iostream>  
#include <string>

int sample_test (double value, int test_num)
{
      static struct pat_data {                  // dynamically allocated structure holding PAT values
            int test_num;                              // one struct for each test_num
            int count;                                    // # of tests measured
            double mean;                              // mean value of all tests
            struct test_data *data;                  // individual data for this test_num
            struct test_data *dfirst;
            struct test_data *dlast;
            struct pat_data *next;
      } pat_data_entry;
      static struct pat_data *pfirst=NULL;
      static struct pat_data *plast=NULL;

      static struct test_data {
            double value;
            struct test_data *next;
      } test_data_entry;

      struct pat_data *pdata;
      static double fudge=0;
      double lvalue;

      printf ("Start of PAT with test_num=%d, value=%e\n",test_num,value);

      fudge += 1e-6;
      lvalue = fudge;

      pdata = pfirst;
      while (pdata) {
            if (pdata->test_num == test_num)
                  goto test_num_matched;
            pdata = pdata->next;
      }
      
      pdata = (struct pat_data *)malloc(sizeof(pat_data_entry));
      if (!pdata) {
            //ERROR in allocating space
      }

      pdata->test_num = test_num;
      pdata->count = 0;

      if (!pfirst) {
            pfirst = pdata;
            plast = pdata;
            pdata->next = NULL;
      } else {
            pdata->next = NULL;
            plast->next = pdata;
            plast = pdata;
      }
      pdata->dfirst = NULL;
      pdata->dlast = NULL;

test_num_matched:
// 1st compiler error is on this line:
      pdata->data = (struct test_data *)malloc(sizeof(test_data_entry));
// error is:
// c:\apps\sample_testing.cpp(72) : error C2440: '=' : cannot convert from 'struct sample_test::test_data *' to 'struct test_data *'
//        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
      if (!pdata->data) {
            //ERROR in allocating space
      }

      pdata->data->value = lvalue;
      ++pdata->count;

      if (!pdata->dfirst) {
            pdata->dfirst = pdata->data;
            pdata->dlast = pdata->data;
            pdata->data->next = NULL;
      } else {
            pdata->data->next = NULL;
            pdata->dlast->next = pdata->data;
            pdata->dlast = pdata->data;
      }

      pdata = pfirst;
      while (pdata) {
            printf ("%5d (%4d): ",pdata->test_num,pdata->count);
            pdata->data = pdata->dfirst;
            while (pdata->data) {
                  printf ("%e, ",pdata->data->value);
                  pdata->data = pdata->data->next;
            }
            printf ("\n");
            pdata = pdata->next;
      }
      return (true);
}

jimdgar
0
Comment
Question by:jimdgar
  • 4
  • 2
6 Comments
 
LVL 30

Expert Comment

by:Axter
ID: 17109647
Hi jimdgar,
>  pdata->data = (struct test_data *)malloc(sizeof(test_data_entry));

In C++, you don't need to use the key word struct when casting.

Try doing it without the keyword in the type cast.

David Maisonave (Axter)
Cheers!
0
 

Author Comment

by:jimdgar
ID: 17109832
David,

That's not it. The same casting works in line 45. I think it has something to do with nesting the structs.

jimdgar
0
 
LVL 30

Expert Comment

by:Axter
ID: 17109868
You need a forward declaration for test_data
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LVL 30

Expert Comment

by:Axter
ID: 17109890
Example:
int sample_test (double value, int test_num)
{
      struct test_data; //Forward declaration .....................*************************
      static struct pat_data {               // dynamically allocated structure holding PAT values
            int test_num;                         // one struct for each test_num
            int count;                              // # of tests measured
            double mean;                         // mean value of all tests
            struct test_data *data;               // individual data for this test_num
            struct test_data *dfirst;
            struct test_data *dlast;
            struct pat_data *next;
      } pat_data_entry;
      static struct pat_data *pfirst=NULL;
      static struct pat_data *plast=NULL;

      static struct test_data {
            double value;
            struct test_data *next;
      } test_data_entry;

      struct pat_data *pdata;
      static double fudge=0;
      double lvalue;

      printf ("Start of PAT with test_num=%d, value=%e\n",test_num,value);

      fudge += 1e-6;
      lvalue = fudge;

      pdata = pfirst;
      while (pdata) {
            if (pdata->test_num == test_num)
                  goto test_num_matched;
            pdata = pdata->next;
      }

      pdata = (pat_data *)malloc(sizeof(pat_data_entry)); //Remove keyword ..........................**********
      if (!pdata) {
            //ERROR in allocating space
      }

      pdata->test_num = test_num;
      pdata->count = 0;

      if (!pfirst) {
            pfirst = pdata;
            plast = pdata;
            pdata->next = NULL;
      } else {
            pdata->next = NULL;
            plast->next = pdata;
            plast = pdata;
      }
      pdata->dfirst = NULL;
      pdata->dlast = NULL;

test_num_matched:
      // 1st compiler error is on this line:
      pdata->data = (test_data *)malloc(sizeof(test_data_entry)); //Remove keyword ..........................**********
      // error is:
      // c:\apps\sample_testing.cpp(72) : error C2440: '=' : cannot convert from 'struct sample_test::test_data *' to 'struct test_data *'
      //        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
      if (!pdata->data) {
            //ERROR in allocating space
      }

      pdata->data->value = lvalue;
      ++pdata->count;

      if (!pdata->dfirst) {
            pdata->dfirst = pdata->data;
            pdata->dlast = pdata->data;
            pdata->data->next = NULL;
      } else {
            pdata->data->next = NULL;
            pdata->dlast->next = pdata->data;
            pdata->dlast = pdata->data;
      }

      pdata = pfirst;
      while (pdata) {
            printf ("%5d (%4d): ",pdata->test_num,pdata->count);
            pdata->data = pdata->dfirst;
            while (pdata->data) {
                  printf ("%e, ",pdata->data->value);
                  pdata->data = pdata->data->next;
            }
            printf ("\n");
            pdata = pdata->next;
      }
      return (true);
}
0
 
LVL 30

Accepted Solution

by:
Axter earned 250 total points
ID: 17109915
Even better, just move the struct.
Example:
int sample_test (double value, int test_num)
{
      static struct test_data {
            double value;
            struct test_data *next;
      } test_data_entry;

      static struct pat_data {               // dynamically allocated structure holding PAT values
            int test_num;                         // one struct for each test_num
            int count;                              // # of tests measured
            double mean;                         // mean value of all tests
            struct test_data *data;               // individual data for this test_num
            struct test_data *dfirst;
            struct test_data *dlast;
            struct pat_data *next;
      } pat_data_entry;
      static struct pat_data *pfirst=NULL;
      static struct pat_data *plast=NULL;

      struct pat_data *pdata;
      static double fudge=0;
      double lvalue;

      printf ("Start of PAT with test_num=%d, value=%e\n",test_num,value);

      fudge += 1e-6;
      lvalue = fudge;

      pdata = pfirst;
      while (pdata) {
            if (pdata->test_num == test_num)
                  goto test_num_matched;
            pdata = pdata->next;
      }

      pdata = (pat_data *)malloc(sizeof(pat_data_entry)); //Remove keyword ..........................**********
      if (!pdata) {
            //ERROR in allocating space
      }

      pdata->test_num = test_num;
      pdata->count = 0;

      if (!pfirst) {
            pfirst = pdata;
            plast = pdata;
            pdata->next = NULL;
      } else {
            pdata->next = NULL;
            plast->next = pdata;
            plast = pdata;
      }
      pdata->dfirst = NULL;
      pdata->dlast = NULL;

test_num_matched:
      // 1st compiler error is on this line:
      pdata->data = (test_data *)malloc(sizeof(test_data_entry)); //Remove keyword ..........................**********
      // error is:
      // c:\apps\sample_testing.cpp(72) : error C2440: '=' : cannot convert from 'struct sample_test::test_data *' to 'struct test_data *'
      //        Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
      if (!pdata->data) {
            //ERROR in allocating space
      }

      pdata->data->value = lvalue;
      ++pdata->count;

      if (!pdata->dfirst) {
            pdata->dfirst = pdata->data;
            pdata->dlast = pdata->data;
            pdata->data->next = NULL;
      } else {
            pdata->data->next = NULL;
            pdata->dlast->next = pdata->data;
            pdata->dlast = pdata->data;
      }

      pdata = pfirst;
      while (pdata) {
            printf ("%5d (%4d): ",pdata->test_num,pdata->count);
            pdata->data = pdata->dfirst;
            while (pdata->data) {
                  printf ("%e, ",pdata->data->value);
                  pdata->data = pdata->data->next;
            }
            printf ("\n");
            pdata = pdata->next;
      }
      return (true);
}
0
 

Author Comment

by:jimdgar
ID: 17110143
Duh, I should have known that.

Thanks, David.

jimdgar
0

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