Write/Save int* to and Read from binary file

[rijia]

Hello! I have this code:

int main()
{
  unsigned int *dWords = NULL;
  int wordCount = 0;
      cout<<"The number of words to load: ";
      cin>>wordCount;  
      genDWords(wordCount,&dWords);//here I allocate memory depending on 
                              //wordCount and change the value of dWords so
                             //it does not point NULL anymore

//Here I want to write something to save *dWords to a binary file, then
//i want to read from it  and access the value(s)
  return 0;
}

I have written something like this but it seems to be wrong and I can't tell what exactly...

     fstream outB("data.bin", ios_base::binary | ios_base::out);
     outB.write((char*)dWords,4*wordCount);
     outB.close();
//Here let's say I exit the program and the binary file is created

//Then I start the program again and want to read the same file so I can
//work with the dWords value I've saved into the file from the upper function 
    
     fstream inB("data.bin", ios_base::binary | ios_base::in);
     inB.read((char*)(&dWords),4*wordCount);
     inB.close();
      

If anyone can give me idea clue or hint please do. I've read all about saving to binary files. The file seems to be saved with the size I expect to but can't read from it or while compiling it gives me the error:

crosses initialization of ‘std::fstream outB’


Thanks in advance.

[kempofighter]

inB.read((char*)(&dWords),4*wordCount);

It is always better to post something more complete but I think that your problem is that you are passing the address of the pointer variable which I don't think you want to do. You want to pass the data contained by the variable which is the starting address of the memory block. Take a look at the example code here.
http://cplusplus.com/reference/iostream/istream/read/

[rijia]

Well that's what I did, but this will only print the contents of the file. I want each double word I create in gendWords() to be saved in the file. Then when start the program again, i want to be able to read from that same file and from there change the *dWords value. Let's put some more code so it makes sense:

void genDWords(int wC,unsigned int ** wrd)//generates random double words and puts them on the screen
{
  if(wC == 0) exit(1);
  srand(time(NULL));
  *wrd = new unsigned int;   
  *wrd = (unsigned int *) malloc(4*wC); //allocating memory for the double words
  for(int i = 0; i<wC; i++)//fills the array with random double words
  {
   (*wrd)[i] = (rand() & 0xFFFFFFFF);
  };
   for(int i = 0; i<wC; i++)//displays the contents of the array
  {
      cout<<dec<<i+1<<". ";
      cout<<hex<<(*wrd)[i]<<endl;      
  };  
}
int main()
{
  unsigned int *dWords = NULL;//declaring *dWords to point NULL  
  int wordCount = 0;
  int act;
  do
  {
  cout<<"1.Generate random double words."<<endl;
  cout<<"2.Calculates the average value of each double word."<<endl;
  cout<<"3.Save to file."<<endl;
  cout<<"4.Read from file."<<endl;
  cout<<"Choose an action: ";
  cin>>act;
  switch (act) 
    {
    case(1): 
      cout<<"\033[22;37mThe number of words to load: ";
      cin>>wordCount;  
      genDWords(wordCount,&dWords);//here I create the dWords and change the value of *dWords by passing it by reference so I 
                                                                    //can use its new value in another function in main()
      break;
    case(2):
      getAvgWords(wordCount,dWords);//here I use the new *dWords value and display something on the screen
      break;
     case(3):
      saveTo(wordCount,dWords);//Here I want to save *dWords which is basically an Array of double words into a binary file 
      break;
     case(5):
      loadFrom(wordCount,&dWords);//after i quit the program and start it again the inital value of *dWords is NULL so
                                                              //here i want to load this file where I stored the *dWords, (the array) pass it to *dWords so it
                                                              //receives the values and be able to use it in function getAvgWords()
       break;
    }
  } while (act!=0);
  return 0;
}

I'm sorry that this is too long but it was the only way to explain what I want to do.
Thanks.

[Duthomhas]

http://www.cplusplus.com/forum/beginner/11431/#msg53963

Good luck!