Windows 命名管道部分读取

Question

当我通过 ReadFile 读取管道并返回部分数据时，是否可能出现这种情况，导致我再次调用 ReadFile 直到达到指定的读取字节数？

Answer 1

PIPE_TYPE_BYTE is set at side which create the named pipe.

At reading side, set PIPE_READMODE_BYTE mode for reading partial data.

In partial reading mode, you can use PIPE_READMODE_BYTE and PIPE_NOWAIT combination to avoid the ReadFile function hangs. lpNumberOfBytesRead parameter can be used to detect if there is more data to read. When there is no data to be read the lpNumberOfBytesRead will be zero if the ReadFile function call success. Otherwise, check the error by calling the GetLastError function.

Based on official sample: Named Pipe Client and Multithreaded Pipe Server .

The client reading related code will be change to:

dwMode = PIPE_READMODE_BYTE | PIPE_NOWAIT;// PIPE_READMODE_MESSAGE;
fSuccess = SetNamedPipeHandleState(
    hPipe,    // pipe handle 
    &dwMode,  // new pipe mode 
    NULL,     // don't set maximum bytes 
    NULL);    // don't set maximum time 

// ...

WCHAR rdWChar;
do
{
    // Read from the pipe. 

    fSuccess = ReadFile(
        hPipe,    // pipe handle 
        &rdWChar,  // buffer to receive reply 
        2,        // test size, read two bytes per read operation
        &cbRead,  // number of bytes read 
        NULL);    // not overlapped 

    if (!fSuccess && GetLastError() != ERROR_MORE_DATA)
        break;

    wprintf(L"%c", rdWChar);
} while (cbRead); // repeat loop if there is more bytes