random access ofstream

[adam2016]

Hi guys I am trying to write to a file so I can access it randomly,I will use indexes to get where each persons data members are stored in a txt file

however this is not working the way I expected it to,when I open up the file there is data written to it,but the data is all numbers with no strings in it even though I did add strings

I'm guessing maybe my math is off? or my logic is off I thought it would work or else I am misusing seekp and tellp?

thanks

  #include <iostream>
#include <fstream>
#include <map>
#include <vector>

using namespace std;


class Index{

  public:

  int locationID;
  int startByte;
  int size;

  Index(){ }
   Index(int s,int siz){

     startByte = s;
     size = siz;

   }

    Index(const Index& other){

       startByte = other.startByte;
       locationID = other.locationID;
       size = other.size;
    }

    Index& operator=(const Index& other){

       startByte = other.startByte;
       locationID = other.locationID;
       size = other.size;

       return *this;
    }
};

class Person{

  public:

      string name;
      int age;

    Person(){}

   Person(string n,int a){

     name = n;
     age = a;
   }

    Person(const Person& other){

        name = other.name;
        age = other.age;
    }
    Person& operator=(const Person& other){

        name = other.name;
        age = other.age;
        return *this;
    }
};

int main()
{

   ofstream out;
   out.open("randomAccess.txt");
   vector<Person> people;
   map<int,Index> index;

   for(int i = 0; i < 50; i++){

       Person temp("adam",i);
       people.push_back(temp);
   }
    try{

     int size = people.size();
     out << size;
     int indexSize(people.size() * 3 * sizeof(int));
     int personStart = (int)(out.tellp() + indexSize + sizeof(int));
     out << personStart;
     int indexStart = (int)out.tellp();
     out << indexStart;

     int startPointer = personStart;
     out.seekp(personStart);

     for(int i = 0; i < people.size(); i++){

        out << people[i].name;
        out << people[i].age;
        startPointer = (int) out.tellp();

        Index ind(startPointer,(int)(out.tellp() - startPointer));
        index[i] = ind;

        startPointer = (int) (out.tellp());
     }

     out.seekp(indexStart);

     for(map<int,Index>::iterator it = index.begin(); it != index.end(); it++ ){

        int number = it->first;

        out << number;
        out << it->second.startByte;
        out << it->second.size;
     }
    }catch(int e){

       cout << e << endl;
    }
}

[adam2016]

after a few couts I have come to the conclusion the my math or calculations are probably off,

but does anybody know why my calculations are off?

[adam2016]

I did the math and I ended up getting the size of the index by int indexSize = (10 * 1) + (40 * 2) + 50 + (3 * 50) + 50 +(3 * 50) + 50 + (50*1) + 50

but my calculations must be wrong,I'm not sure why though as each character is a bye so I thought I took every byte into consideration

anyway when I subtracted 199 I seemed to get the correct position,but how what was I missing?

int indexSize = (10 * 1) + (40 * 2) + 50 + (3 * 50) + 50 +(3 * 50) + 50 + (50*1) + 50-199;

[Enoizat]

I’ve no problem to confess I got lost after a few lines of your try-block, so I didn’t even try to do the math. But I wonder why you are so interested in the sizeof(int), since you open your file as text, not binary, therefore you should consider what you write are characters.
I hope the following code could help to clarify my question:

#include <fstream>
#include <iostream>
#include <limits>

void waitForEnter();

int main()
{
    std::ofstream out("ra.txt");
    if(!out) {
        std::cout << "can't open output file.\n";
        return 0;
    }
    std::streampos pos1 = out.tellp();
    std::cout << "At beginning,                tellp() says " << pos1 << '\n';
    out << 'a';
    std::streampos pos2 = out.tellp();
    std::cout << "After writing  'a'           tellp() says " << pos2
              << " which is " << pos2 - pos1 << " distant\n";
    out << 9;
    pos1 = out.tellp();
    std::cout << "After writing   9            tellp() says " << pos1
              << " which is " << pos1 - pos2 << " distant\n";
    out << 13;
    pos2 = out.tellp();
    std::cout << "After writing  13            tellp() says " << pos2
              << " which is " << pos2 - pos1 << " distant\n";
    out << 666.13;
    pos1 = out.tellp();
    std::cout << "After writing 666.13         tellp() says " << pos1
              << " which is " << pos1 - pos2 << " distant\n";
    out << "Hi, adam2016"; // 12 characters
    pos2 = out.tellp();
    std::cout << "After writing \"Hi, adam2016\" tellp() says " << pos2
              << " which is " << pos2 - pos1 << " distant\n";
    waitForEnter();
}

void waitForEnter()
{
    std::cout << "\nPress ENTER to continue...\n";
    std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}

Output

At beginning,                tellp() says 0
After writing  'a'           tellp() says 1 which is 1 distant
After writing   9            tellp() says 2 which is 1 distant
After writing  13            tellp() says 4 which is 2 distant
After writing 666.13         tellp() says 10 which is 6 distant
After writing "Hi, adam2016" tellp() says 22 which is 12 distant

Press ENTER to continue...

ra.txt:
a913666.13Hi, adam2016

[adam2016]

hey Enoziat

very good point I noticed this too after a while lol,I forgot that I was working with text rather than binary so each character is one byte long

thanks