OutputDataReceived has no data?

mc 4,111

var processInfo = new ProcessStartInfo
{
    FileName = _path,
    Arguments = " ",
    UseShellExecute = false,
    RedirectStandardError = true,
        RedirectStandardInput = true,
    RedirectStandardOutput = true,
    CreateNoWindow = true
};
_process.StartInfo = processInfo;
_process.OutputDataReceived += _process_OutputDataReceived;
_process.ErrorDataReceived += _process_ErrorDataReceived;
_process.Start();
_process.BeginOutputReadLine();
_process.BeginErrorReadLine();

but the data is in _process_ErrorDataReceived not _process_OutputDataReceived

why?

David Lowndes 2,510 Reputation points MVP

2023-10-07T13:20:16.1266667+00:00

Do you know if the spawned process is writing to the standard output rather than standard error?
mc 4,111 Reputation points

2023-10-08T00:48:48.62+00:00

Thank you but I do not know what you mean?
David Lowndes 2,510 Reputation points MVP

2023-10-08T09:19:23.8033333+00:00

A console program can write to the standard output (normally the console) and standard error (also normally the console), if it's writing its data output to the standard error stream (for some unknown reason), that would explain your findings.
Hui Liu-MSFT 47,341 Reputation points Microsoft Vendor

2023-10-09T07:47:04.98+00:00

Hi,@mc . Welcome Microsoft Q&A. The behavior you're describing, where the output data is received in the ErrorDataReceived event handler instead of the OutputDataReceived event handler, can occur when you have an issue with the way the external process is writing data to its output streams. Here are some common reasons and solutions:

Buffering: Some processes buffer their output differently, and this can affect when the data is received. It's possible that the process is buffering its output differently, causing data to be received in an unexpected order.

External Process Behavior: The behavior depends on how the external process is writing data to its output streams. Ensure that the external process is correctly writing standard output to the stdout stream and standard error to the stderr stream.

Debugging the External Process: You can also debug the external process separately to check how it's handling output. Make sure it's writing data to standard output as expected.

Output Data Format: Ensure that the output data format produced by the external process doesn't contain any unexpected characters or formatting that could affect the way data is received.

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OutputDataReceived has no data?