dprintf vs returning in C++

Question

Disclaimer that I know nothing about C++ so bear with me... I am looking at some existing code which prints a continuous stream of strings describing the position of a VR controller.

void CMainApplication::printDevicePositionalData(const char * deviceName, vr::HmdMatrix34_t posMatrix, vr::HmdVector3_t position, vr::HmdQuaternion_t quaternion)
{
    LARGE_INTEGER qpc; // Query Performance Counter for Acquiring high-resolution time stamps.
                       // From MSDN: "QPC is typically the best method to use to time-stamp events and 
                       // measure small time intervals that occur on the same system or virtual machine.
    QueryPerformanceCounter(&qpc);
 
    // Print position and quaternion (rotation).
    dprintf("\n%lld, %s, x = %.5f, y = %.5f, z = %.5f, qw = %.5f, qx = %.5f, qy = %.5f, qz = %.5f",
        qpc.QuadPart, deviceName,
        position.v[0], position.v[1], position.v[2],
        quaternion.w, quaternion.x, quaternion.y, quaternion.z);
}

When I run the compiled exe in powershell it does not seem to print anything. Only if I run .\this_program.exe | tee output.txt do I see anything, as it simultaneously writes to a .txt file.

How can I change to above code to return these values, as I want to be able to read them in realtime with python using subprocess and stdout. Thanks

What is `dprintf`? Where is it from? Why was it selected? – Robert Andrzejuk Dec 26 '20 at 11:35 — Robert Andrzejuk, Dec 26 '20 at 11:35

score 2 · Answer 1 · answered Dec 26 '20 at 11:40

2

If you want to print to the console output, you should not be using:

dprintf - This function prints a formatted string to the command window for the debugger.

With C++, IO streams should be used (std::cout, std::clog, or std::cerr). Or fallback to printf.

answered Dec 26 '20 at 11:40

Robert Andrzejuk

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Thanks. How can I change it to return the string rather than print it? – Dude Dec 26 '20 at 11:43
@largest_prime_is_463035818 As I understand it, OP wants to use python to read the standard console output. (Not use a library) – Robert Andrzejuk Dec 26 '20 at 11:44
@Dude What do you mean: return it? – Robert Andrzejuk Dec 26 '20 at 11:44
Perhaps a different question to ask is.. why if I run this in poweshell using just `.\this_program.exe` does it run the exe but show nothing in the console, yet adding `| tee output.txt` shows the values? – Dude Dec 26 '20 at 11:47
@Dude try `.\this_program.exe 2>&1` – Robert Andrzejuk Dec 26 '20 at 11:53
https://stackoverflow.com/questions/16772842/what-is-the-difference-between-cout-cerr-clog-of-iostream-header-in-c-when – Robert Andrzejuk Dec 26 '20 at 11:54
@Dude the problem is with `dprintf`. Why was it selected? – Robert Andrzejuk Dec 26 '20 at 12:00
Thanks, though unfortunately that has not seemed to make a difference. Ultimately I want to be able to run this exe in python using `subprocess.run(["this_program.exe"], shell=True, capture_output=True)` and have access to the strings of coordinates is it outputting. – Dude Dec 26 '20 at 12:02
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/226438/discussion-between-dude-and-robert-andrzejuk). – Dude Dec 26 '20 at 12:04
Then don't use `dprintf`. Use `std::cout` or printf. – Robert Andrzejuk Dec 26 '20 at 12:07

dprintf vs returning in C++

1 Answers1