C++/File/Binary File

Binary Files

<source lang="cpp">

1. include <iostream>

using namespace std;

1. include <fstream>

int main () {

long start,end;
ifstream myfile ("test.txt", ios::in|ios::binary);
start = myfile.tellg();
myfile.seekg (0, ios::end);
end = myfile.tellg();
myfile.close();
cout << "size of " << "test.txt";
cout << " is " << (end-start) << " bytes.\n";
return 0;

}

 </source>

binary input and output with integers

<source lang="cpp">

1. include <fstream>
2. include <iostream>

using namespace std; const int MAX = 100; int buff[MAX];

int main(){

  for(int j=0; j<MAX; j++)   
     buff[j] = j;              
                             
  ofstream os("edata.dat", ios::binary);  
                             
  os.write( reinterpret_cast<char*>(buff), MAX*sizeof(int) );  
  os.close();                
 
  for(int j=0; j<MAX; j++)       
     buff[j] = 0;  
                             
  ifstream is("edata.dat", ios::binary);  
  is.read( reinterpret_cast<char*>(buff), MAX*sizeof(int) );  
  for(int j=0; j<MAX; j++){      
     if( buff[j] != j ){ 
        cerr << "Data is incorrect\n"; return 1;
     }
  }     
  cout << "Data is correct\n";  
  return 0;  

}

 </source>

reading a complete binary file

<source lang="cpp">

1. include <iostream>
2. include <fstream>

using namespace std; ifstream::pos_type size; char * memblock; int main () {

 ifstream file ("example.txt", ios::in|ios::binary|ios::ate);
 if (file.is_open()){
   size = file.tellg();
   memblock = new char [size];
   file.seekg (0, ios::beg);
   file.read (memblock, size);
   file.close();
   cout << "the complete file content is in memory";
   delete[] memblock;
 }else 
   cout << "Unable to open file";
 return 0;

}

 </source>

seeks particular person in file

<source lang="cpp">

1. include <fstream>

 #include <iostream>  
 using namespace std;  
 class person      
 {  
    protected:  
       char name[80];
       int age;      
    public:  
       void getData(){  
          cout << "\n   Enter name: "; cin >> name;  
          cout << "   Enter age: "; cin >> age;  
       }  
       void showData(void){  
          cout << "\n   Name: " << name;  
          cout << "\n   Age: " << age;  
       }  
 };  
 int main(){  
    person pers;
    ifstream infile;
    infile.open("GROUP.DAT", ios::in | ios::binary);
   
    infile.seekg(0, ios::end);     
    int endposition = infile.tellg();        
    int n = endposition / sizeof(person);    
    cout << "\nThere are " << n << " persons in file";  
   
    cout << "\nEnter person number: ";  
    cin >> n;  
    int position = (n-1) * sizeof(person);  
    infile.seekg(position);        
                                   
    infile.read( reinterpret_cast<char*>(&pers), sizeof(pers) );  
    pers.showData();               
    cout << endl;  
    return 0;  
    }
 
   
 </source>

Write numbers to a binary file and read them back

<source lang="cpp">

1. include <iostream>
2. include <fstream>

using namespace std; int main(void){

  float fnum[4] = {11.22, -33.44, 55.66, 77.88};
  int i;
  ofstream out("numbers.asc", ios::out | ios::binary);
  if(!out){
     cout << "Cannot open file.";
     exit (1);
  }
  out.write((char *) &fnum, sizeof(fnum));
  out.close();
  for (i=0; i<4; i++)
     fnum[i] = 0.0;
  ifstream in("numbers.asc", ios::in | ios::binary);
  if(!in) {
     cout << "Cannot open file.";
     exit (1);
  }
  in.read((char *) &fnum, sizeof(fnum));
  cout << in.gcount() << " bytes read." << endl;
  for (i=0; i<4; i++)
     cout << fnum[i] << " ";
  in.close();

}

 </source>