Thread: Another 'dereferencing pointer to incomplete type'

Essence of the code regarding issue:

Code:

typedef struct BMS_Chkmem{
  int elemsize;
} BMS_CHKMEM;  

typedef struct BMS_Blkmem{
  BMS_CHKMEM* chkmemhash[1013];
} BMS_BLKMEM;

typedef struct SCIP_Mem{
  BMS_BLKMEM* setmem;
} SCIP_MEM;

void* allocMemory(size)
{
  void* ptr;
  ptr = malloc(size)
  return ptr;
}

BMS_BLKMEM* createBlockMemory(void)
{
  int i;
  BMS_BLKMEM* blkmem;
  blkmem = allocMemory(sizeof(*(blkmem)));

  for (i=0; i < 1013; i++)
  {
    blkmem->chkmemhash[i] = NULL;
  }

  return blkmem;
}

void memCreate(SCIP_MEM** mem)
{
  mem = allocMemory(sizeof(**(mem)));

  (*mem)->setmem = createBlockMemory();

  if ( (*mem)->setmem->chkmemhash[60] == NULL)
    printf("Is null\n");
  else
    printf("Is not null\n");
}

int main(void)
{
  SCIP_MEM* mem;
  memCreate(&mem);
  return 0;
}

The above code is simple the essence of what I'm using, I'm not even sure if it would compile, but I hope it contains everything needed.

memCreate is called, and is passed a pointer of a higher struct, which at the time is NULL, the idea being to allocate it some memory, and initialize it. When I try to compile the code that this is taken from, I get an error of:

dereferening pointer to incomplete type

This error relates to:

if ( (*mem)->setmem->chkmemhash[60] == NULL)

From what I can see, this should work, but clearly I'm overlooking something.

Well, I was able to make small modifications to the posted code and it worked just fine, so it must be something in the code you didn't post.

My code:

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct BMS_Chkmem{
  int elemsize;
} BMS_CHKMEM;  

typedef struct BMS_Blkmem{
  BMS_CHKMEM* chkmemhash[1013];
} BMS_BLKMEM;

typedef struct SCIP_Mem{
  BMS_BLKMEM* setmem;
} SCIP_MEM;

void* allocMemory(size)
{
  void* ptr = malloc(size);
  return ptr;
}

BMS_BLKMEM* createBlockMemory(void)
{
  int i;
  BMS_BLKMEM* blkmem;
  blkmem = allocMemory(sizeof(*(blkmem)));

  for (i=0; i < 1013; i++)
  {
    blkmem->chkmemhash[i] = NULL;
  }

  return blkmem;
}

void memCreate(SCIP_MEM** mem)
{
  mem = allocMemory(sizeof(**(mem)));

  (*mem)->setmem = createBlockMemory();

  if ( (*mem)->setmem->chkmemhash[60] == NULL)
    printf("Is null\n");
  else
    printf("Is not null\n");
}

int main(void)
{
    SCIP_MEM *mem;
    memCreate(&mem);
    return 0;
}

My output:
Is null

Originally Posted by itsme86

Well, I was able to make small modifications to the posted code and it worked just fine, so it must be something in the code you didn't post.

Well, the code I posted is a summary of what happens to variables related to the issue I had, thus I left out a LOT of code which I deemed to be unrelated.

Interestingly, when I compile the code that you posted (gcc -Wall prog.c -o prog) and run, I get a seg fault at:

Code:

(*mem)->setmem = createBlockMemory();

Ie, it appears to occur duing the assignment, rather than during the function execution, as the function executes fine all the way through to "return blkmem". Any reason why I would get a seg fault and you not? I'm just wondering if this difference could explain my original issue.

I honestly cannot see any errors in the code I posted. Maybe someone else can spot something. I even tried compiling with gcc -Wall -std=c99 -pedantic and the only warning I get is that the type of size defaults to int (here: void* allocMemory(size)).

Originally Posted by Bayint Naung

Looking at how you call this function.

Code:

void memCreate(SCIP_MEM** mem)
{
  mem = allocMemory(sizeof(**(mem)));  
// shouldn't it be   *mem = allocMemory( sizeof(**mem) );  since you can't modify mem
// to change in caller!

  (*mem)->setmem = createBlockMemory();

  if ( (*mem)->setmem->chkmemhash[60] == NULL)
    printf("Is null\n");
  else
    printf("Is not null\n");
}

Ahh, good catch! Can't believe I did that. Must have been day-before-thanksgiving-blindness.

Yup, it crashes right after the before assignment pointer check.