Storing numerical value from a binary file into an array- C++

问题

I am trying to read numerical data from a binary file containing 100 double values and store it in an array called myArray. When I print myArray nothing is being shown, as if myArray has never been filled. Any help is appreciated.

int main() 
{
    int file_len; 
    ifstream infile; 
    infile.open("mybinfile.bin", ios::binary | ios::in); 
    if (!infile.is_open()) 
    {
    cout << "Error in opening the file. " << endl;
    }
    else
    {
        const int file_len = 100;

        std::vector<char> myVect;
        myVect.resize(file_len);

        int i = 0;
        infile.read((char *) (&temp), sizeof(char));
        myVect[i] = temp;
        while(!infile.eof())
        {

            myVect[i] = temp;
            i++;
            infile.read((char *)  (&temp), sizeof(char));
        }
        for (int i = 0; i < 100 ; i++)
        {cout << i << ": " << myVect[i]<< endl;}
    }    
    infile.close();

return 0;
}

回答1:

Here

infile.read((char*)&myArray, file_len * sizeof(double));

You pass the pointer to the pointer to double. It should be

infile.read((char*)myArray, file_len * sizeof(double));

Makes me wonder why you didn't see a crash, since writing into random memory almost never turns out well.

回答2:

Here is one example of brute-force serialization and de-serialization. Note that serialization in general is tricky, due to e.g. endianness, different floating-point formats, conversion between decimal text representations and binary and whatnot.

#include <fstream>

using std::string;
using std::ofstream;
using std::ifstream;
using std::cout;

string fname("/tmp/doubles.bin");

void write_doubles()
{
    ofstream of;
    of.open(fname.c_str(), std::ios::binary | std::ios::out);

    double arr[100];

    for (int i = 0; i < 100; i++)
    {
        arr[i] = static_cast<double>(i+100);
    }

    of.write((char*)arr, 100*sizeof(double));
}

void read_doubles()
{
    ifstream ifs;
    ifs.open(fname.c_str(), std::ios::binary | std::ios::in);

    double arr[100];
    ifs.read((char*)arr, 100*sizeof(double));


    for (int i = 0; i < 100; i++)
    {
        cout << "Arr[i]: " << arr[i] << ", ";
    }

    cout << '\n';


}

int main()
{
    write_doubles();
    read_doubles();

    return 0;
}

来源：https://stackoverflow.com/questions/26735428/storing-numerical-value-from-a-binary-file-into-an-array-c

标签

c++

file-io

binary