Piping a data file with cat to a C++ program

Question

I'm looking for some help piping a file (16-bit signed little endian integers raw data) from the command line to my program:

cat data.dat | myprogram

Then it should convert the data to 16 bit signed integers. It works for the first 12 values. The 13th value is wrong, followed by zeros.

The second problem is that the program seems to enter the while loop only once.

I am using Windows + MinGW.

My Code:

#include <iostream>
using namespace std;

#define DEFAULT_BUF_LENGTH (16 * 16384)

int main(int argc, char* argv[]) 
{
    char buf[DEFAULT_BUF_LENGTH];

    while(cin >> buf) 
    {
        int16_t* data = (int16_t*) buf; //to int

        for(int i=0;i<18;i++)
        {
            cout << data[i] << endl;
        }
    }
    return 0;
}

Output:

Thanks for your help!

Check this discussion. On Windows stdin is opened in text mode and certain byte indicates end of file, the solution is to reopen it in binary mode. — dewaffled
You can't use >> it converts line endings. You have to use unformatted input functions like cin.read(). en.cppreference.com/w/cpp/io/basic_istream — Galik

Alexander Balabin Alexander Balabin · Accepted Answer · 2015-07-19T20:53:37

You might try to use read() instead of the >> operator, which is generally for formatted input. Also checking how much data was actually read is useful:

#include <iostream>
using namespace std;

#define DEFAULT_BUF_LENGTH (16 * 16384)

int main(int argc, char* argv[]) 
{
    char buf[DEFAULT_BUF_LENGTH];

    for(;;) 
    {
        cin.read(buf, sizeof(buf));
        int size = cin.gcount();
        if (size == 0) break;

        int16_t* data = (int16_t*) buf; //to int

        for(int i=0;i<size/sizeof(int16_t);i++)
        {
            cout << hex << data[i] << endl;
        }
    }
    return 0;
}

Piping a data file with cat to a C++ program

2 Answers