如何处理 "dir" 的输出？

Question

我编写了一个程序，实现了一个微小的 shell 来处理来自用户的命令。如果输入的命令被识别为内部命令，我的程序就执行这个命令。

这些命令作为内部函数实现，它们的输出由另一个内部函数处理，该函数能够将文本发送到控制台和/或文件以进行日志记录。

如果输入的命令无法识别，我会尝试将输入的命令作为 windows 命令的一部分执行 shell，例如: cmd dir 会执行 dir 命令，输出会打印在控制台上。这是通过 CreateProcess 完成的。到目前为止，我没有指定 STARTUPINFO 参数的成员 hStdError、hStdOutput 和 hStdInput。

我尝试实施和改编 Creating a Child Process with Redirected Input and Output 的示例。

我没有使用他们的子进程实现，但尝试将 dir 命令的输出获取到我的应用程序中：

#include "pch.h"
#include <windows.h>

#define BUFSIZE 512

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



PROCESS_INFORMATION piProcInfo;
STARTUPINFO siStartInfo;
void CreateChildProcess()
// Create a child process that uses the previously created pipes for STDIN and STDOUT.
{
    TCHAR szCmdline[] = TEXT("cmd /c dir q:\Sicherung\Bilder /s");
    BOOL bSuccess = FALSE;

    // 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)
        return; // ErrorExit(("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 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);

    for (;;)
    {
        DWORD objectstat = WAIT_TIMEOUT;
        //do
        //{
        //  objectstat = WaitForSingleObject(piProcInfo.hProcess, 0);
        //} while (objectstat != WAIT_OBJECT_0);
        memset(&chBuf[0], 0x00, BUFSIZE);
        bSuccess = ReadFile(g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
        if (!bSuccess)
            break;

        bSuccess = WriteFile(hParentStdOut, chBuf,
            dwRead, &dwWritten, NULL);
        if (!bSuccess) 
            break;
        if (dwRead == 0)
            break;
    }
}
int main()
{
    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))
        return -1;// ErrorExit("StdoutRd CreatePipe");

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

    if (!SetHandleInformation(g_hChildStd_OUT_Rd, HANDLE_FLAG_INHERIT, 0))
        return -2;// ErrorExit(("Stdout SetHandleInformation"));

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

    if (!CreatePipe(&g_hChildStd_IN_Rd, &g_hChildStd_IN_Wr, &saAttr, 0))
        return -3 ;// ErrorExit(("Stdin CreatePipe"));

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

    if (!SetHandleInformation(g_hChildStd_IN_Wr, HANDLE_FLAG_INHERIT, 0))
        return -4;// ErrorExit(("Stdin SetHandleInformation"));

    // Create the child process. 
    CreateChildProcess();
    ReadFromPipe();
    CloseHandle(piProcInfo.hProcess);
    CloseHandle(piProcInfo.hThread);
    return 0;
}

我知道，问题出在 ReadFile 上。我无法确定何时处理了 dir 命令的所有输出。检查 dwRead 是否为 0 或 BUFSIZE 不起作用。 dwRead永远不会变成0，有可能小于BUFSIZE，因为dir命令不够快

那么，我应该如何结束管道数据的处理？

Answer 1

好的，在 google 中搜索了一些不同的术语后，我想出了这个 link 到 Whosebug ;) : How to read output from cmd.exe using CreateProcess() and CreatePipe()

Ian Boyd 在那里写道：

Once you've launched your child process: be sure to close those ends of the pipe you no longer need.

result = CreateProcess(...);



//CreateProcess demands that we close these two populated handles when we're done with them. We're done with them.

CloseHandle(pi.hProcess);

CloseHandle(pi.hThread);



/*

   We've given the console app the writable end of the pipe during CreateProcess; we don't need it anymore.

   We do keep the handle for the *readable* end of the pipe; as we still need to read from it.

   The other reason to close the writable-end handle now is so that there's only one out-standing reference to the writeable end: held by the console app.

   When the app closes, it will close the pipe, and ReadFile will return code 109 (The pipe has been ended).

   That's how we'll know the console app is done. (no need to wait on process handles with buggy infinite waits)

*/

CloseHandle(g_hChildStd_OUT_Wr);

g_hChildStd_OUT_Wr = 0;

CloseHandle(g_hChildStd_IN_Rd);

g_hChildStd_OUT_Wr = 0;

The common problem with most solutions is that people try to wait on a process handle. There are many problems with this; the main one being that if you wait for the child the terminate, the child will never be able to terminate.

关闭不需要的句柄后 ReadFile 按预期工作。

如何处理 "dir" 的输出？

How do I process the output of "dir"?

c

windows

redirect

readfile