Question

我已经按照示例here从管道读取，但ReadFile失败，GetLastError（）显示管道坏了。
我已经在程序的早期创建并使用了（成功）一个管道，但我关闭了所有的句柄，并为新管道使用了全新的变量，以确保。任何想法为什么这不起作用？

HANDLE g_hChildStd_OUT_Rd2 = NULL;
HANDLE g_hChildStd_OUT_Wr2 = NULL;
SECURITY_ATTRIBUTES saAttr2; 
STARTUPINFO si2;
PROCESS_INFORMATION pi2;

ZeroMemory( &si2, sizeof(si2) );
si2.cb = sizeof(si2);
ZeroMemory( &pi2, sizeof(pi2) );
//create pipe
saAttr2.nLength = sizeof(SECURITY_ATTRIBUTES); 
saAttr2.bInheritHandle = TRUE; 
saAttr2.lpSecurityDescriptor = NULL; 
CreatePipe(&g_hChildStd_OUT_Rd2, &g_hChildStd_OUT_Wr2, &saAttr2, 0);
//create child process
bSuccess = FALSE;
memset(szCmdLine, 0, MAX_PATH);
sprintf(szCmdLine, "ffmpeg.exe -i output.mp3");
ZeroMemory( &pi2, sizeof(PROCESS_INFORMATION) );
ZeroMemory( &si2, sizeof(STARTUPINFO) );
si2.cb = sizeof(STARTUPINFO); 
si2.hStdOutput = g_hChildStd_OUT_Wr2;
si2.dwFlags |= STARTF_USESTDHANDLES;
CreateProcess(NULL, szCmdLine, NULL, NULL, TRUE, 0, NULL, NULL, &si2, &pi2);
//read from pipe
CloseHandle(g_hChildStd_OUT_Wr2);
memset(chBuf, 0, BUFSIZE);
for (;;) 
{ 
  bSuccess = ReadFile( g_hChildStd_OUT_Rd2, chBuf, BUFSIZE, &dwRead, NULL);
  [bSuccess is 0 and GetLastError() returns error 109]
  ........

Answer 1

当另一端关闭管道时，“断管”是正常错误。在您的情况下，这意味着没有“另一端”，或者其他应用程序没有向其stdout写入任何内容。我已将您的代码修改为可编译的测试用例 - 有两种情况ReadFile在没有为我读取任何数据的情况下失败：

CreateProcess失败了。我添加了assert，以便可以识别问题。这当然会导致管道破裂。
该过程不会向标准输出写入任何内容。它可能会写入其标准错误流。我也将stderr重定向到了管道，正如我的echo示例所示，这将在管道的另一端接收两个流。

代码：

#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#include <assert.h>
#include <stdio.h>
#include <string.h>

#define BUFSIZE 200

int main(void)
{
    BOOL bSuccess;
    char szCmdLine[MAX_PATH];
    char chBuf[BUFSIZE];
    DWORD dwRead;
    HANDLE g_hChildStd_OUT_Rd2 = NULL;
    HANDLE g_hChildStd_OUT_Wr2 = NULL;
    SECURITY_ATTRIBUTES saAttr2; 
    STARTUPINFO si2;
    PROCESS_INFORMATION pi2;

    ZeroMemory( &si2, sizeof(si2) );
    si2.cb = sizeof(si2);
    ZeroMemory( &pi2, sizeof(pi2) );
    //create pipe
    saAttr2.nLength = sizeof(SECURITY_ATTRIBUTES); 
    saAttr2.bInheritHandle = TRUE; 
    saAttr2.lpSecurityDescriptor = NULL; 
    assert(CreatePipe(&g_hChildStd_OUT_Rd2, &g_hChildStd_OUT_Wr2, &saAttr2, 0));
    //create child process
    bSuccess = FALSE;
    memset(szCmdLine, 0, MAX_PATH);
    sprintf(szCmdLine, "cmd /c echo output && echo error>&2");
    ZeroMemory( &pi2, sizeof(PROCESS_INFORMATION) );
    ZeroMemory( &si2, sizeof(STARTUPINFO) );
    si2.cb = sizeof(STARTUPINFO); 
    si2.hStdOutput = g_hChildStd_OUT_Wr2;
    si2.hStdError = g_hChildStd_OUT_Wr2; // also add the pipe as stderr!
    si2.dwFlags |= STARTF_USESTDHANDLES;
    assert(CreateProcess(NULL, szCmdLine, NULL, NULL, TRUE, 0, NULL, NULL, &si2, &pi2));
    //read from pipe
    CloseHandle(g_hChildStd_OUT_Wr2);
    memset(chBuf, 0, BUFSIZE);
    for (;;) 
    { 
        bSuccess = ReadFile( g_hChildStd_OUT_Rd2, chBuf, BUFSIZE, &dwRead, NULL);
        printf("%d %lu 0x%08lx\n", bSuccess, dwRead, GetLastError());
        if (bSuccess)
            printf("\t'%*s'\n", (int)dwRead, chBuf);
        else
            break;
    }
    return 0;
}

win32中的断管（WinAPI）

1 个答案: