我怎样才能读取子进程的输出？(How can I read a child process'

我写了试图通过一个管道读取子进程的命令行输出的功能。这应该是一个简单的子集的MSDN创建具有重定向输入和输出的文章子进程，但我清楚地做某种类型的错误。

下面块ReadFile的（...）调用永远没有如果我之前还是应该用信号通知子进程结束的WaitForSingleObject的（...）调用后放置不管。

我已阅读所有的建议“使用异步ReadFile的”的答案，我愿意接受这个建议，如果有人能够给我一些想法如何被一个管道来完成。虽然我不明白为什么需要这种情况下异步I / O。

#include "stdafx.h"
#include <string>
#include <windows.h>

unsigned int launch( const std::string & cmdline );

int _tmain(int argc, _TCHAR* argv[])
{
    launch( std::string("C:/windows/system32/help.exe") );  
    return 0;
}

void print_error( unsigned int err )
{
    char* msg = NULL;
    FormatMessageA(
        FORMAT_MESSAGE_ALLOCATE_BUFFER | 
        FORMAT_MESSAGE_FROM_SYSTEM |
        FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL,
        err,
        MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
        (LPSTR)&msg,
        0, NULL );
    std::cout << "------ Begin Error Msg ------" << std::endl;
    std::cout << msg << std::endl;
    std::cout << "------  End Error Msg  ------" << std::endl;

    LocalFree( msg );
}

unsigned int launch( const std::string & cmdline )
{
    TCHAR cl[_MAX_PATH*sizeof(TCHAR)]; 
    memset( cl, 0, sizeof(cl) );
    cmdline.copy( cl, (_MAX_PATH*sizeof(TCHAR)) - 1);    

    HANDLE stdoutReadHandle = NULL;
    HANDLE stdoutWriteHandle = NULL;

    SECURITY_ATTRIBUTES saAttr; 
    memset( &saAttr, 0, sizeof(saAttr) ); 
    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES); 
    saAttr.bInheritHandle = TRUE; 
    saAttr.lpSecurityDescriptor = NULL; 

    // Create a pipe for the child process's STDOUT. 
    if ( ! CreatePipe(&stdoutReadHandle, &stdoutWriteHandle, &saAttr, 5000) )      
        throw std::runtime_error( "StdoutRd CreatePipe" ); 
    // Ensure the read handle to the pipe for STDOUT is not inherited.
    if ( ! SetHandleInformation(stdoutReadHandle, HANDLE_FLAG_INHERIT, 0) )
        throw std::runtime_error( "Stdout SetHandleInformation" ); 

    STARTUPINFO startupInfo; 
    memset( &startupInfo, 0, sizeof(startupInfo) ); 
    startupInfo.cb = sizeof(startupInfo);
    startupInfo.hStdError = stdoutWriteHandle;
    startupInfo.hStdOutput = stdoutWriteHandle;
    startupInfo.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
    startupInfo.dwFlags |= STARTF_USESTDHANDLES;

    char* rawEnvVars = GetEnvironmentStringsA();

    //__asm _emit 0xcc;

    PROCESS_INFORMATION processInfo;
    memset( &processInfo, 0, sizeof(processInfo) );

    std::cout << "Start [" << cmdline << "]" << std::endl;
    if ( CreateProcessA( 0, &cl[0], 0, 0, false, 
        CREATE_NO_WINDOW | CREATE_UNICODE_ENVIRONMENT, 
        rawEnvVars, 0, &startupInfo, &processInfo ) )
    {       
        //CloseHandle( stdoutWriteHandle );
        DWORD wordsRead;
        char tBuf[257] = {'\0'};
        bool success = true;
        std::string outBuf("");
        unsigned int t;
        while(success) {
            //__asm _emit 0xcc;
            std::cout << "Just before ReadFile(...)" << std::endl;
            success = ReadFile( stdoutReadHandle, tBuf, 256, &wordsRead, NULL);
            (t=GetLastError())?print_error(t):t=t;
            std::cout << "Just after ReadFile(...) | read " << wordsRead<< std::endl;
            std::cout << ".";
            if( success == false ) break;
            outBuf += tBuf;
            tBuf[0] = '\0';
        }
        std::cout << "output = [" << outBuf << "]" << std::endl;


        if ( WaitForSingleObject( processInfo.hProcess, INFINITE ) == WAIT_OBJECT_0 )
        {
            unsigned int exitcode = 0;
            GetExitCodeProcess( processInfo.hProcess, (LPDWORD)&exitcode );                
            std::cout << "exitcode = [" << exitcode << "]" << std::endl;

            //__asm _emit 0xcc;
            CloseHandle( processInfo.hProcess );
            CloseHandle( processInfo.hThread );

            return exitcode;
        }
    }
    else
    {
        DWORD procErr = GetLastError();
        std::cout << "FAILED TO CREATE PROCESS!" << std::endl;
        print_error( procErr );
    }
    return -1;
} // end launch()

Answer 1:

有代码中的一些错误，但最重要的是，您所指定FALSE的bInheritHandles参数CreateProcess 。新工艺不能使用管道如果不把手继承它。为了使被继承的句柄，在bInheritHandles参数必须是TRUE 和手柄必须启用继承。

其他问题：

你指定CREATE_UNICODE_ENVIRONMENT而是传递一个ANSI环境块。需要注意的是容易通过NULL为lpEnvironment ，并让系统复制环境块给你。你不需要在这种情况下，指定CREATE_UNICODE_ENVIRONMENT，即使你在Unicode模式编译。
同样，如果你调用CreateProcessA你应该使用STARTUPINFOA。
你不零终止tBuf每次周围循环，所以你会在你的输出缓冲器获得虚假多余的字符。
您需要关闭stdoutWriteHandle您输入读循环之前，或者你会不会当子退出知道。（或者你可以使用异步IO和检查进程退出明确。）
GetLastError()是不确定的，如果一个API函数调用成功，所以如果你只应调用它ReadFile返回FALSE 。（当然，在这种情况下，这是纯粹的化妆品，因为你不采取行动上的错误代码。）

作为参考，这是我纠正你的代码的版本。我已经把它变成普通的C（对不起！），因为这是我很熟悉。我编译和在Unicode模式下进行测试，但我认为它不应该在ANSI模式下修改工作了。

#define _WIN32_WINNT _WIN32_WINNT_WIN7
#include <windows.h>
#include <stdio.h>

void launch(const char * cmdline_in)
{
    PROCESS_INFORMATION processInfo;
    STARTUPINFOA startupInfo; 
    SECURITY_ATTRIBUTES saAttr; 

    HANDLE stdoutReadHandle = NULL;
    HANDLE stdoutWriteHandle = NULL;

    char cmdline[256];
    char outbuf[32768];
    DWORD bytes_read;
    char tBuf[257];

    DWORD exitcode;

    strcpy_s(cmdline, sizeof(cmdline), cmdline_in);

    memset(&saAttr, 0, sizeof(saAttr));
    saAttr.nLength = sizeof(SECURITY_ATTRIBUTES); 
    saAttr.bInheritHandle = TRUE; 
    saAttr.lpSecurityDescriptor = NULL; 

    // Create a pipe for the child process's STDOUT. 
    if (!CreatePipe(&stdoutReadHandle, &stdoutWriteHandle, &saAttr, 5000))
    {
        printf("CreatePipe: %u\n", GetLastError());
        return;
    }

    // Ensure the read handle to the pipe for STDOUT is not inherited.
    if (!SetHandleInformation(stdoutReadHandle, HANDLE_FLAG_INHERIT, 0))
    {
        printf("SetHandleInformation: %u\n", GetLastError());
        return;
    }

    memset(&startupInfo, 0, sizeof(startupInfo));
    startupInfo.cb = sizeof(startupInfo);
    startupInfo.hStdError = stdoutWriteHandle;
    startupInfo.hStdOutput = stdoutWriteHandle;
    startupInfo.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
    startupInfo.dwFlags |= STARTF_USESTDHANDLES;

    // memset(&processInfo, 0, sizeof(processInfo));  // Not actually necessary

    printf("Starting.\n");

    if (!CreateProcessA(NULL, cmdline, NULL, NULL, TRUE,
        CREATE_NO_WINDOW, NULL, 0, &startupInfo, &processInfo))
    {
        printf("CreateProcessA: %u\n", GetLastError());
        return;
    }

    CloseHandle(stdoutWriteHandle);

    strcpy_s(outbuf, sizeof(outbuf), "");

    for (;;) {
        printf("Just before ReadFile(...)\n");
        if (!ReadFile(stdoutReadHandle, tBuf, 256, &bytes_read, NULL))
        {
            printf("ReadFile: %u\n", GetLastError());
            break;
        }
        printf("Just after ReadFile, read %u byte(s)\n", bytes_read);
        if (bytes_read > 0)
        {
            tBuf[bytes_read] = '\0';
            strcat_s(outbuf, sizeof(outbuf), tBuf);
        }
    }

    printf("Output: %s\n", outbuf);

    if (WaitForSingleObject(processInfo.hProcess, INFINITE) != WAIT_OBJECT_0)
    {
        printf("WaitForSingleObject: %u\n", GetLastError());
        return;
    }

    if (!GetExitCodeProcess(processInfo.hProcess, &exitcode))
    {
        printf("GetExitCodeProcess: %u\n", GetLastError());
        return;
    }

    printf("Exit code: %u\n", exitcode);

    CloseHandle( processInfo.hProcess );
    CloseHandle( processInfo.hThread );

    return;
}

int main(int argc, char** argv)
{
    launch("C:\\windows\\system32\\help.exe");
    return 0;
}