Violation thrown when trying to read from binary file

Question

I have a structure with all the data for a contestant. I have a function where I input the value of contestants' data like team name, team hometown, team foundation date and etc. Then I have a function to write that data to a binary file and also a function to read that data from the binary file.

My structure:

struct Team {
    string teamName;
    string teamHometown;
    int foundedDay{};
    int foundedMonth{};
    int foundedYear{};
    int matchPlayed{};
    int matchLost{};
    int goalsFor{};
    int goalsAgainst{};
    int goalDifference{};
    int Points{};
};

My write and read functions:

void writeBinary(Team* T, int& contestantCount) {
    Team Data;
    ofstream File;
    File.open("Data.bin", ios::binary | ios::out);
    if (File.is_open()) {
        File.write(reinterpret_cast<char*>(&Data), sizeof(Team));
        File.close();
        system("cls");
        cout << "|--------------------------------------------------------------------------------------------|" << endl;
        cout << "                            DATA SUCCESSFULLY SAVED TO BINARY FILE" << endl;
        cout << "|--------------------------------------------------------------------------------------------|" << endl << endl;
        system("pause");
    }
    else {
        system("cls");
        cout << "|--------------------------------------------------------------------------------------------|" << endl;
        cout << "                                COULD NOT OPEN BINARY DATA FILE" << endl;
        cout << "|--------------------------------------------------------------------------------------------|" << endl << endl;
        system("pause");
    }
}

void readBinary(Team* T, int& contestantCount) {
    Team Data;
    ifstream File;
    File.open("Data.bin", ios::binary | ios::in);
    if (File.is_open()) {
        File.read(reinterpret_cast<char*>(&Data), sizeof(Team));
        File.close();
        system("cls");
        cout << "|--------------------------------------------------------------------------------------------|" << endl;
        cout << "                             SHOWING SAVED DATA FROM BINARY FILE" << endl;
        cout << "|--------------------------------------------------------------------------------------------|" << endl << endl;
    }
    else {
        system("cls");
        cout << "|--------------------------------------------------------------------------------------------|" << endl;
        cout << "                                COULD NOT OPEN BINARY DATA FILE" << endl;
        cout << "|--------------------------------------------------------------------------------------------|" << endl << endl;
        system("pause");
    }
    cout << Data.teamName << endl;
    system("pause");
}

I assume that my write function works fine since it doesn't give me any violations in the code and I can see that the .bin file is created with the contents in it. When I run the read function though, it gives me this violation and it gives me "Read access violation" in the terminal.

Here is a picture of the result in the console when I run the read function and a picture of the violation that it gives me after the function reaches its end.

Console output screenshot Violation screenshot

What you are attempting is [object serialization](https://stackoverflow.com/questions/234724), and implementing it is not as simple as your code presumes. Writing a pointer, for example, does not ensure that the pointer will be valid later. — Drew Dormann, Jan 14 '21 at 17:43

score 0 · Answer 1 · answered Jan 14 '21 at 17:39

0

You cannot write the whole struct Team in a fie because std::string may allocate memory. When you are writing std::string and reading it back, the pointers you read will not point to the right place.

Instead, you need to write and read one struct member at a time, and do something special for std::string. The whole exercise is known as serialization. It is not automatic in C++.

answered Jan 14 '21 at 17:39

Eugene

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I will look into that. Thanks for the assistance. – Aleksandar Haralanov Jan 14 '21 at 17:46

Violation thrown when trying to read from binary file

1 Answers1