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I'm trying to write to a hid device using signal11's hidapi (here). In my troubleshooting, I've noticed that part of a string isn't being displayed to the console. Here is a sample of my code

//device is a hid device and is assigned to in another part of the program.
//dataBuffer is a struct with only a char array called "buffer" and an int which is the size of the array called "size"
void DeviceCommands::Write(hid_device* device, dataBuffer* buf)
{
    std::cout << "Attempting write >> buffer...\n";
    buf->buffer[0] = 0;
    std::cout << "Written to buffer...\n" << "writing buffer to device\n";
    int res = hid_write(device, buf->buffer, sizeof(buf->buffer));
    std::cout << "Write success: "  + '\n';
    std::cout << "Write complete\n";
}

I'm expecting for the console to return the following:

Attempting write >> buffer...
Written to buffer...
writing buffer to device
Write success: (0 if the write succeeds, -1 if it fails)
Write complete

But instead, this happens:

Attempting write >> buffer...
Written to buffer...
writing buffer to device
ess: Write complete

The "Write succ", result, and the line break are missing, I'm somewhat new to c++ but I have experience with c#. I'm just confused and some help would be much appreciated, thanks in advance and ask if you need more information!

NefariousTechSupport_1
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2 Answers2

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This line:

std::cout << "Write success: "  + '\n';

will print the string "Write success: " with an offset of 10 characters, which is the ascii value of \n. Hence you see ess on the screen.

You probably want:

std::cout << "Write success: " << res << "\n";

assuming res returns 0 or -1 as needed.

cigien
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Do not 'add' a character to a string. It will not do what you expect.

Here you are thinking you are adding the line feed character to your string "Write success" when in fact you are telling the compiler to take your constant string and only stream from the 10th character. Remember a constant string here is just an array of characters and the single character '\n' is converted to the number 10.

You are also missing the result out of the streaming.

So your second to last line should read:

std::cout << "Write success: " << res <<  std::endl;
user8241961
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