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createprocess 親と子の MSDN の例を実行しますが、子入力に情報を書き込むため (cmd に出力して確認したもの)、正しく動作しませんが、printf( "\n->Contents of子プロセスの STDOUT:\n\n"); 呼び出すとき

ReadFromPipe();

アプリケーションが呼び出された cmd では、何も受信しませんが、待機します。ctrl + cを実行した場合にのみ終了します。何が理由でしょうか？

#include "stdafx.h"
#include <windows.h> 
#include <tchar.h>
#include <stdio.h> 
#include <strsafe.h>
#include <iostream> //only for cout

#define BUFSIZE 4096 

HANDLE g_hChildStd_IN_Rd = NULL;
HANDLE g_hChildStd_IN_Wr = NULL;
HANDLE g_hChildStd_OUT_Rd = NULL;
HANDLE g_hChildStd_OUT_Wr = NULL;

HANDLE g_hInputFile = NULL;

void CreateChildProcess(void); 
void WriteToPipe(void); 
void ReadFromPipe(void); 
void ErrorExit(PTSTR); 

int _tmain(int argc, TCHAR *argv[]) 
{ 
   SECURITY_ATTRIBUTES saAttr; 

   printf("\n->Start of parent execution.\n");

// Set the bInheritHandle flag so pipe handles are inherited. 

   saAttr.nLength = sizeof(SECURITY_ATTRIBUTES); 
   saAttr.bInheritHandle = TRUE; 
   saAttr.lpSecurityDescriptor = NULL; 

// Create a pipe for the child process's STDOUT. 

   if ( ! CreatePipe(&g_hChildStd_OUT_Rd, &g_hChildStd_OUT_Wr, &saAttr, 0) ) 
      ErrorExit(TEXT("StdoutRd CreatePipe")); 

// Ensure the read handle to the pipe for STDOUT is not inherited.

   if ( ! SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0) )
      ErrorExit(TEXT("Stdout SetHandleInformation")); 

// Create a pipe for the child process's STDIN. 

   if (! CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0)) 
      ErrorExit(TEXT("Stdin CreatePipe")); 

// Ensure the write handle to the pipe for STDIN is not inherited. 

   if ( ! SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0) )
      ErrorExit(TEXT("Stdin SetHandleInformation")); 

// Create the child process. 

   CreateChildProcess();

// Get a handle to an input file for the parent. 
// This example assumes a plain text file and uses string output to verify data flow. 

   if (argc == 1) 
      ErrorExit(TEXT("Please specify an input file.\n")); 

   g_hInputFile = CreateFile(
       argv[1], 
       GENERIC_READ, 
       0, 
       NULL, 
       OPEN_EXISTING, 
       FILE_ATTRIBUTE_READONLY, 
       NULL); 

   if ( g_hInputFile == INVALID_HANDLE_VALUE ) 
      ErrorExit(TEXT("CreateFile")); 

// Write to the pipe that is the standard input for a child process. 
// Data is written to the pipe's buffers, so it is not necessary to wait
// until the child process is running before writing data.

   WriteToPipe(); 
   printf( "\n->Contents of %s written to child STDIN pipe.\n", argv[1]);

// Read from pipe that is the standard output for child process. 

   printf( "\n->Contents of child process STDOUT:\n\n");
   ReadFromPipe(); 

   printf("\n->End of parent execution.\n");

// The remaining open handles are cleaned up when this process terminates. 
// To avoid resource leaks in a larger application, close handles explicitly. 

   return 0; 
} 

void CreateChildProcess()
// Create a child process that uses the previously created pipes for STDIN and STDOUT.
{ 
   TCHAR szCmdline[]=TEXT("C:\\Windows\\notepad.exe");//TEXT("C:\\Windows\\System32\\cmd.exe");
   PROCESS_INFORMATION piProcInfo; 
   STARTUPINFO siStartInfo;
   BOOL bSuccess = FALSE; 
    std::cout<<"\nCreateChildProcess.\n";
// Set up members of the PROCESS_INFORMATION structure. 

   ZeroMemory( &piProcInfo, sizeof(PROCESS_INFORMATION) );

// Set up members of the STARTUPINFO structure. 
// This structure specifies the STDIN and STDOUT handles for redirection.

   ZeroMemory( &siStartInfo, sizeof(STARTUPINFO) );
   siStartInfo.cb = sizeof(STARTUPINFO); 
   siStartInfo.hStdError = g_hChildStd_OUT_Wr;
   siStartInfo.hStdOutput = g_hChildStd_OUT_Wr;
   siStartInfo.hStdInput = g_hChildStd_IN_Rd;
   siStartInfo.dwFlags |= STARTF_USESTDHANDLES;

// Create the child process. 

   bSuccess = CreateProcess(NULL, 
      szCmdline,     // command line 
      NULL,          // process security attributes 
      NULL,          // primary thread security attributes 
      TRUE,          // handles are inherited 
      0,             // creation flags 
      NULL,          // use parent's environment 
      NULL,          // use parent's current directory 
      &siStartInfo,  // STARTUPINFO pointer 
      &piProcInfo);  // receives PROCESS_INFORMATION 

   // If an error occurs, exit the application. 
   if ( ! bSuccess ) 
      ErrorExit(TEXT("CreateProcess"));
   else 
   {
      // Close handles to the child process and its primary thread.
      // Some applications might keep these handles to monitor the status
      // of the child process, for example. 

      CloseHandle(piProcInfo.hProcess);
      CloseHandle(piProcInfo.hThread);
   }
}

void WriteToPipe(void) 

// Read from a file and write its contents to the pipe for the child's STDIN.
// Stop when there is no more data. 
{ 
   DWORD dwRead, dwWritten; 
   CHAR chBuf[BUFSIZE];
   BOOL bSuccess = FALSE;

   for (;;) 
   { 
      bSuccess = ReadFile(g_hInputFile, chBuf, BUFSIZE, &dwRead, NULL);
      if ( ! bSuccess || dwRead == 0 ) break; 

      bSuccess = WriteFile(g_hChildStd_IN_Wr, chBuf, dwRead, &dwWritten, NULL);
      if ( ! bSuccess ) break; 
   } 
    std::cout<<"\nchBuf: "<<chBuf<<std::endl; 
// Close the pipe handle so the child process stops reading. 

   if ( ! CloseHandle(g_hChildStd_IN_Wr) ) 
      ErrorExit(TEXT("StdInWr CloseHandle")); 
} 

void ReadFromPipe(void) 

// Read output from the child process's pipe for STDOUT
// and write to the parent process's pipe for STDOUT. 
// Stop when there is no more data. 
{ 
   DWORD dwRead, dwWritten; 
   CHAR chBuf[BUFSIZE]; 
   BOOL bSuccess = FALSE;
   HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);

        bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, 4, &dwRead, NULL); 
        std::cout<<"\nchBuf: "<<chBuf<<std::endl;

   /*for (int i=0;i<2;i++) //read twice
   { 
      bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
      if( ! bSuccess || dwRead == 0 ) break; 
      std::cout<<"\nchBuf: "<<chBuf<<std::endl;

      bSuccess = WriteFile(hParentStdOut, chBuf, 
                           dwRead, &dwWritten, NULL);
      if (! bSuccess ) break;
   } */

} 

void ErrorExit(PTSTR lpszFunction) 

// Format a readable error message, display a message box, 
// and exit from the application.
{ 
    LPVOID lpMsgBuf;
    LPVOID lpDisplayBuf;
    DWORD dw = GetLastError(); 

    FormatMessage(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | 
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        dw,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPTSTR) &lpMsgBuf,
        0, NULL );

    lpDisplayBuf = (LPVOID)LocalAlloc(LMEM_ZEROINIT, 
        (lstrlen((LPCTSTR)lpMsgBuf)+lstrlen((LPCTSTR)lpszFunction)+40)*sizeof(TCHAR)); 
    StringCchPrintf((LPTSTR)lpDisplayBuf, 
        LocalSize(lpDisplayBuf) / sizeof(TCHAR),
        TEXT("%s failed with error %d: %s"), 
        lpszFunction, dw, lpMsgBuf); 
    MessageBox(NULL, (LPCTSTR)lpDisplayBuf, TEXT("Error"), MB_OK); 

    LocalFree(lpMsgBuf);
    LocalFree(lpDisplayBuf);
    ExitProcess(1);
}
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1 に答える 1

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その理由は、stdout に書き込むことのない GUI アプリケーション notepad.exe を開始しているためです。そのため、stdout は開いたままになっており、何も書き込まれていないため、ReadFileブロックへの呼び出しは何かが現れるのを待っています。コメントアウトした cmd.exe に戻ると、ReadFromPipe呼び出しから出力が得られます。

また、 ReadFromPipe 関数は、ほとんどジャンクを出力するだけです。それをテストするために、次のように変更しました。

void ReadFromPipe(void) 

// Read output from the child process's pipe for STDOUT
// and write to the parent process's pipe for STDOUT. 
// Stop when there is no more data. 
{ 
   DWORD dwRead;
   CHAR chBuf[BUFSIZE]; 
   BOOL bSuccess = TRUE;

   do
   {
        dwRead = 0;
        bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUFSIZE-1, &dwRead, NULL); 
        chBuf[dwRead] = '\0';
        std::cout<<"\nchBuf: "<<chBuf<<std::endl;
   } while (bSuccess && dwRead > 0);
}
于 2012-04-21T14:48:48.203 に答える