Error in reading fom a binary file!

[mohammed alhadi]

Hi All,

Can any body tell me how to fix the errors in this program? I am reading integer values from a binary file and displaying them!

int i;
ifstream::pos_type size;
 
        ifstream pBinaryFile ("binaryfile.bin", ios::in|ios::binary|ios::ate); //other format to read from the binary file
 
 
        if (!pBinaryFile)
        {
            printf("Unable to open file!");
            return 1;
        }
 
 
        size = pBinaryFile.tellg(); //to get the size of the binary file in bytes
        file.seekg (0, ios::beg); // and then go to the beginning of the file to read from it
 
        for ( counter=1; counter <= (size/sizeof(int)); counter++) 
        // divided over sizeof because I want to read as long as the number of int values
        {
        fread(&i,sizeof(i),1,pBinaryFile);
            printf("%d ",i);    
 
        }
       cout<<endl;
 
       fclose(pBinaryFile);

errors that I have:
error C2040: 'pBinaryFile' : 'class std::basic_ifstream<char,struct std::char_traits<char> >' differs in levels of indirection from 'struct _iobuf *'
error C2228: left of '.tellg' must have class/struct/union type
error C2065: 'file' : undeclared identifier
error C2228: left of '.seekg' must have class/struct/union type

[hype261]

Are you sure you are including the right header file for the ifstream?

I believe it is defined in <fstream>

Also you need to replace file with pBinaryFile at line 15

[mohammed alhadi]

Thank u Hype 261, I have changed the operation of reading from a file to an array as follows: but it give me rabish!

int i;

fstream file ("binaryfile.bin", ios::in|ios::binary);


if (!file)
{
printf("Unable to open file!");
return 1;
}

file.seekg(0, ios::end); // position get-ptr 0 bytes from end
ios::pos_type size = file.tellg(); // get-ptr position is now same as file size

int *p;
int si=int(size/sizeof(int));
p= new int[si];
file.read((char *) &p, sizeof p);

for(i=0; i<si; i++) // show values read from file
cout << p[i] << " ";

file.close();

return 0;

[weaknessforcats]

si is a single int. You have () instead of [].

[mohammed alhadi]

Hi weaknessforcats, si is just the number of integer values in he binary file ... I calculated it by taking the number of bytes in the file and dividing it by the size of int... and then cast it to int .... don't u think it is correct?!

[hype261]

First you are not going back to the begining of the file after you figure out the file size.

file.seekg (0, ios::beg);
 

Secondly I am not entirely sure that the file.read code is going to work correcly. Generally when I do file manipulation I use getline and stringstreams to make sure the data is good.

[weaknessforcats]

You should be calculating the number of bytes in a file and then reading these bytes into an array of the correct size.

Then you typecast the array name to the correct type. Of course, as with all reads, this presupposes you already know the layout of the file.

So if there are 1000 byes then read the bytes into a char array of 1000 char. Then typecast the array address as an int*. This would give you 250 int.

[mohammed alhadi]

I made this but it also doesn't work, it give me big numbers!
file.seekg(0, ios::end);
ios::pos_type size = file.tellg();
file.seekg (0, ios::beg);

char *p;
p= new char[size];
int *q;
q=new int [size/sizeof(int)];
q=(int*)&p;

for(i=0; i<size; i++)
cout << q[i] << " ";

file.close();

return 0;

[johny10151981]

simple reading method would be

//you did
file.read((char *) &p, sizeof p);
// but it would be
file.read((char *)p, size); //size is the length of file. 
 

but yet it has a little bug

say what if size%sizeof int!=0? which mean you have some extra bytes. it would cause you segmentation fault. to fix this issue.

you can allocate your int array as

p = new int[size/sizeof(int) + (size%(sizeof int)!=0)];

if the modulus == 0 then it wont create an extra 4 bytes otherwise it would or you can skip the last extra bytes.

this way:

file.read((char *)p, size-(size%sizeof int));