Question

I want to save the state of my structs as a binary file and load them again.
My structs look like this:

typedef struct
{
  uint8_t pointerLength;
  uint8_t *pointer;
  uint8_t NumBla;
  uinT16 Bla[MAX_NUM_Bla];
   ...
}
BAR_STRUCT, *BAR;

typedef struct
{
  int numBar;
  BAR bars[MAX_NUM_BAR];
}
FOO_STRUCT, *FOO;

Saving is no problem, but restoring the state.
Iam at the point where the bytestring from the file is on the heap and a pointer is pointing to the first adress of this string.
And I do as follows:

const void* dataPointer //points to adress in heap
unsigned char* bytePointer = (unsigned char*)dataPointer;

FOO foo = (FOO_STRUCT*)bytePointer;
bytePointer += sizeof(FOO_STRUCT);  

for (int i=0; i < MAX_NUM_BAR; i++) {
    foo->bars[i] = (BAR_STRUCT*)bytePointer;
}

The last assignment doesn’t work and I get an EXC_BAD_ACCESS.
Because bars is an array of pointers i need to correct the adresses of each element is pointing to. Because they are not valid anymore. So I try to assign the adress of the object I saved in the bytesteam to foo->bars[i];
But I can not change foo->bars[i] at all. Accessing works but but assigning a new adress doesn’t.
I wonder why.

Edit:
Iam working on OSX so to write bytes to file i use NSData:

bool saveCurrentState( FOO foo){
  NSMutableData *data = [NSMutableData data];
  [data appendBytes:templates length:sizeof(FOO_STRUCT)];
  for (int i=0; i < MAX_NUM_BAR; i++){
    [data appendBytes:&foo->bar[i] length:sizeof(INT_BAR_STRUCT)];
    if( foo->bar[i] != NULL )
      [data appendBytes:foo->bar[i]->pointer length:sizeof(uint8_t)*foo->bar[i]->length];
    ...
  }
}

I can’t really change the structs since they are used in a lib, which i don’t really have access too. I am especially interested in why it is not working as expected.
As you can see I copy the whole struct including the pointer itself and adding the structures the pointer were pointing to to the byte string. Hope this give a bit more clarification.

When reading byte stream to setup the structs i just need the change the values of the array with the new address and that for some reason doesn’t want to work.

Edit:
Iam also saving/reading the file with NSData:

NSData* data = [NSData dataWithContentsOfFile:@"path/to/file"];
const void* dataPointer = [data bytes];

Answer 1

Looks like what you are after is a serialization library. Try something like protocol buffers or tpl (choice depends on your exact needs, check the docs).

This previous question seems to do a decent job of covering some of the issues.