假设是POSIX，捕获stdout的简单代码:

#include <sys/wait.h>
#include <unistd.h>
#include <string>
#include <vector>

std::string qx(const std::vector<std::string>& args) {
  int stdout_fds[2];
  pipe(stdout_fds);

  int stderr_fds[2];
  pipe(stderr_fds);

  const pid_t pid = fork();
  if (!pid) {
    close(stdout_fds[0]);
    dup2(stdout_fds[1], 1);
    close(stdout_fds[1]);

    close(stderr_fds[0]);
    dup2(stderr_fds[1], 2);
    close(stderr_fds[1]);

    std::vector<char*> vc(args.size() + 1, 0);
    for (size_t i = 0; i < args.size(); ++i) {
      vc[i] = const_cast<char*>(args[i].c_str());
    }

    execvp(vc[0], &vc[0]);
    exit(0);
  }

  close(stdout_fds[1]);

  std::string out;
  const int buf_size = 4096;
  char buffer[buf_size];
  do {
    const ssize_t r = read(stdout_fds[0], buffer, buf_size);
    if (r > 0) {
      out.append(buffer, r);
    }
  } while (errno == EAGAIN || errno == EINTR);

  close(stdout_fds[0]);

  close(stderr_fds[1]);
  close(stderr_fds[0]);

  int r, status;
  do {
    r = waitpid(pid, &status, 0);
  } while (r == -1 && errno == EINTR);

  return out;
}

为获得更多功能，欢迎代码贡献:

https://github.com/ericcurtin/execxx

waqas的答案的c++流实现:

#include <istream>
#include <streambuf>
#include <cstdio>
#include <cstring>
#include <memory>
#include <stdexcept>
#include <string>

class execbuf : public std::streambuf {
    protected:
        std::string output;
        int_type underflow(int_type character) {
            if (gptr() < egptr()) return traits_type::to_int_type(*gptr());
            return traits_type::eof();
        }
    public:
        execbuf(const char* command) {
            std::array<char, 128> buffer;
            std::unique_ptr<FILE, decltype(&pclose)> pipe(popen(command, "r"), pclose);
            if (!pipe) {
                throw std::runtime_error("popen() failed!");
            }
            while (fgets(buffer.data(), buffer.size(), pipe.get()) != nullptr) {
                this->output += buffer.data();
            }
            setg((char*)this->output.data(), (char*)this->output.data(), (char*)(this->output.data() + this->output.size()));
        }
};

class exec : public std::istream {
    protected:
        execbuf buffer;
    public:
        exec(char* command) : std::istream(nullptr), buffer(command, fd) {
            this->rdbuf(&buffer);
        }
};

这段代码通过stdout捕获所有输出。如果你只想捕获stderr，那么像这样传递你的命令:

sh -c '<your-command>' 2>&1 > /dev/null

如果你想同时捕获stdout和stderr，那么命令应该是这样的:

sh -c '<your-command>' 2>&1

我会使用popen() (++waqas)。

但有时你需要阅读和写作……

似乎没有人再用困难的方式做事了。

(假设是Unix/Linux/Mac环境，或者是带有POSIX兼容层的Windows…)

enum PIPE_FILE_DESCRIPTERS
{
  READ_FD  = 0,
  WRITE_FD = 1
};

enum CONSTANTS
{
  BUFFER_SIZE = 100
};

int
main()
{
  int       parentToChild[2];
  int       childToParent[2];
  pid_t     pid;
  string    dataReadFromChild;
  char      buffer[BUFFER_SIZE + 1];
  ssize_t   readResult;
  int       status;

  ASSERT_IS(0, pipe(parentToChild));
  ASSERT_IS(0, pipe(childToParent));

  switch (pid = fork())
  {
    case -1:
      FAIL("Fork failed");
      exit(-1);

    case 0: /* Child */
      ASSERT_NOT(-1, dup2(parentToChild[READ_FD], STDIN_FILENO));
      ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDOUT_FILENO));
      ASSERT_NOT(-1, dup2(childToParent[WRITE_FD], STDERR_FILENO));
      ASSERT_IS(0, close(parentToChild [WRITE_FD]));
      ASSERT_IS(0, close(childToParent [READ_FD]));

      /*     file, arg0, arg1,  arg2 */
      execlp("ls", "ls", "-al", "--color");

      FAIL("This line should never be reached!!!");
      exit(-1);

    default: /* Parent */
      cout << "Child " << pid << " process running..." << endl;

      ASSERT_IS(0, close(parentToChild [READ_FD]));
      ASSERT_IS(0, close(childToParent [WRITE_FD]));

      while (true)
      {
        switch (readResult = read(childToParent[READ_FD],
                                  buffer, BUFFER_SIZE))
        {
          case 0: /* End-of-File, or non-blocking read. */
            cout << "End of file reached..."         << endl
                 << "Data received was ("
                 << dataReadFromChild.size() << "): " << endl
                 << dataReadFromChild                << endl;

            ASSERT_IS(pid, waitpid(pid, & status, 0));

            cout << endl
                 << "Child exit staus is:  " << WEXITSTATUS(status) << endl
                 << endl;

            exit(0);


          case -1:
            if ((errno == EINTR) || (errno == EAGAIN))
            {
              errno = 0;
              break;
            }
            else
            {
              FAIL("read() failed");
              exit(-1);
            }

          default:
            dataReadFromChild . append(buffer, readResult);
            break;
        }
      } /* while (true) */
  } /* switch (pid = fork())*/
}

您还可能希望使用select()和非阻塞读取。

fd_set          readfds;
struct timeval  timeout;

timeout.tv_sec  = 0;    /* Seconds */
timeout.tv_usec = 1000; /* Microseconds */

FD_ZERO(&readfds);
FD_SET(childToParent[READ_FD], &readfds);

switch (select (1 + childToParent[READ_FD], &readfds, (fd_set*)NULL, (fd_set*)NULL, & timeout))
{
  case 0: /* Timeout expired */
    break;

  case -1:
    if ((errno == EINTR) || (errno == EAGAIN))
    {
      errno = 0;
      break;
    }
    else
    {
      FAIL("Select() Failed");
      exit(-1);
    }

  case 1:  /* We have input */
    readResult = read(childToParent[READ_FD], buffer, BUFFER_SIZE);
    // However you want to handle it...
    break;

  default:
    FAIL("How did we see input on more than one file descriptor?");
    exit(-1);
}

我不明白为什么popen/pclose从Code::Blocks/MinGW中消失了。所以我使用CreateProcess()和CreatePipe()来解决这个问题。

以下是对我有效的解决方案:

//C++11
#include <cstdio>
#include <iostream>
#include <windows.h>
#include <cstdint>
#include <deque>
#include <string>
#include <thread>

using namespace std;

int SystemCapture(
    string         CmdLine,    //Command Line
    string         CmdRunDir,  //set to '.' for current directory
    string&        ListStdOut, //Return List of StdOut
    string&        ListStdErr, //Return List of StdErr
    uint32_t&      RetCode)    //Return Exit Code
{
    int                  Success;
    SECURITY_ATTRIBUTES  security_attributes;
    HANDLE               stdout_rd = INVALID_HANDLE_VALUE;
    HANDLE               stdout_wr = INVALID_HANDLE_VALUE;
    HANDLE               stderr_rd = INVALID_HANDLE_VALUE;
    HANDLE               stderr_wr = INVALID_HANDLE_VALUE;
    PROCESS_INFORMATION  process_info;
    STARTUPINFO          startup_info;
    thread               stdout_thread;
    thread               stderr_thread;

    security_attributes.nLength              = sizeof(SECURITY_ATTRIBUTES);
    security_attributes.bInheritHandle       = TRUE;
    security_attributes.lpSecurityDescriptor = nullptr;

    if (!CreatePipe(&stdout_rd, &stdout_wr, &security_attributes, 0) ||
            !SetHandleInformation(stdout_rd, HANDLE_FLAG_INHERIT, 0)) {
        return -1;
    }

    if (!CreatePipe(&stderr_rd, &stderr_wr, &security_attributes, 0) ||
            !SetHandleInformation(stderr_rd, HANDLE_FLAG_INHERIT, 0)) {
        if (stdout_rd != INVALID_HANDLE_VALUE) CloseHandle(stdout_rd);
        if (stdout_wr != INVALID_HANDLE_VALUE) CloseHandle(stdout_wr);
        return -2;
    }

    ZeroMemory(&process_info, sizeof(PROCESS_INFORMATION));
    ZeroMemory(&startup_info, sizeof(STARTUPINFO));

    startup_info.cb         = sizeof(STARTUPINFO);
    startup_info.hStdInput  = 0;
    startup_info.hStdOutput = stdout_wr;
    startup_info.hStdError  = stderr_wr;

    if(stdout_rd || stderr_rd)
        startup_info.dwFlags |= STARTF_USESTDHANDLES;

    // Make a copy because CreateProcess needs to modify string buffer
    char      CmdLineStr[MAX_PATH];
    strncpy(CmdLineStr, CmdLine.c_str(), MAX_PATH);
    CmdLineStr[MAX_PATH-1] = 0;

    Success = CreateProcess(
        nullptr,
        CmdLineStr,
        nullptr,
        nullptr,
        TRUE,
        0,
        nullptr,
        CmdRunDir.c_str(),
        &startup_info,
        &process_info
    );
    CloseHandle(stdout_wr);
    CloseHandle(stderr_wr);

    if(!Success) {
        CloseHandle(process_info.hProcess);
        CloseHandle(process_info.hThread);
        CloseHandle(stdout_rd);
        CloseHandle(stderr_rd);
        return -4;
    }
    else {
        CloseHandle(process_info.hThread);
    }

    if(stdout_rd) {
        stdout_thread=thread([&]() {
            DWORD  n;
            const size_t bufsize = 1000;
            char         buffer [bufsize];
            for(;;) {
                n = 0;
                int Success = ReadFile(
                    stdout_rd,
                    buffer,
                    (DWORD)bufsize,
                    &n,
                    nullptr
                );
                printf("STDERR: Success:%d n:%d\n", Success, (int)n);
                if(!Success || n == 0)
                    break;
                string s(buffer, n);
                printf("STDOUT:(%s)\n", s.c_str());
                ListStdOut += s;
            }
            printf("STDOUT:BREAK!\n");
        });
    }

    if(stderr_rd) {
        stderr_thread=thread([&]() {
            DWORD        n;
            const size_t bufsize = 1000;
            char         buffer [bufsize];
            for(;;) {
                n = 0;
                int Success = ReadFile(
                    stderr_rd,
                    buffer,
                    (DWORD)bufsize,
                    &n,
                    nullptr
                );
                printf("STDERR: Success:%d n:%d\n", Success, (int)n);
                if(!Success || n == 0)
                    break;
                string s(buffer, n);
                printf("STDERR:(%s)\n", s.c_str());
                ListStdErr += s;
            }
            printf("STDERR:BREAK!\n");
        });
    }

    WaitForSingleObject(process_info.hProcess,    INFINITE);
    if(!GetExitCodeProcess(process_info.hProcess, (DWORD*) &RetCode))
        RetCode = -1;

    CloseHandle(process_info.hProcess);

    if(stdout_thread.joinable())
        stdout_thread.join();

    if(stderr_thread.joinable())
        stderr_thread.join();

    CloseHandle(stdout_rd);
    CloseHandle(stderr_rd);

    return 0;
}

int main()
{
    int            rc;
    uint32_t       RetCode;
    string         ListStdOut;
    string         ListStdErr;

    cout << "STARTING.\n";

    rc = SystemCapture(
        "C:\\Windows\\System32\\ipconfig.exe",    //Command Line
        ".",                                     //CmdRunDir
        ListStdOut,                              //Return List of StdOut
        ListStdErr,                              //Return List of StdErr
        RetCode                                  //Return Exit Code
    );
    if (rc < 0) {
        cout << "ERROR: SystemCapture\n";
    }

    cout << "STDOUT:\n";
    cout << ListStdOut;

    cout << "STDERR:\n";
    cout << ListStdErr;

    cout << "Finished.\n";

    cout << "Press Enter to Continue";
    cin.ignore();

    return 0;
}

下面可能是一个可移植的解决方案。它遵循标准。

#include <iostream>
#include <fstream>
#include <string>
#include <cstdlib>
#include <sstream>

std::string ssystem (const char *command) {
    char tmpname [L_tmpnam];
    std::tmpnam ( tmpname );
    std::string scommand = command;
    std::string cmd = scommand + " >> " + tmpname;
    std::system(cmd.c_str());
    std::ifstream file(tmpname, std::ios::in | std::ios::binary );
    std::string result;
    if (file) {
        while (!file.eof()) result.push_back(file.get())
            ;
        file.close();
    }
    remove(tmpname);
    return result;
}

// For Cygwin

int main(int argc, char *argv[])
{
    std::string bash = "FILETWO=/cygdrive/c/*\nfor f in $FILETWO\ndo\necho \"$f\"\ndone ";
    std::string in;
    std::string s = ssystem(bash.c_str());
    std::istringstream iss(s);
    std::string line;
    while (std::getline(iss, line))
    {
        std::cout << "LINE-> " + line + "  length: " << line.length() << std::endl;
    }
    std::cin >> in;
    return 0;
}

您可以在使用管道运行脚本后获得输出。当我们需要子进程的输出时，我们使用管道。

int my_func() {
    char ch;
    FILE *fpipe;
    FILE *copy_fp;
    FILE *tmp;
    char *command = (char *)"/usr/bin/my_script my_arg";
    copy_fp = fopen("/tmp/output_file_path", "w");
    fpipe = (FILE *)popen(command, "r");
    if (fpipe) {
        while ((ch = fgetc(fpipe)) != EOF) {
            fputc(ch, copy_fp);
        }
    }
    else {
        if (copy_fp) {
            fprintf(copy_fp, "Sorry there was an error opening the file");
        }
    }
    pclose(fpipe);
    fclose(copy_fp);
    return 0;
}

这就是你要运行的脚本。将它与脚本所接受的参数一起放在命令变量中(如果没有参数，就什么都没有)。以及您想要捕获脚本输出的文件，将其放在copy_fp中。

popen运行你的脚本并将输出放到fpipe中然后你可以将所有内容复制到输出文件中。

通过这种方式，您可以捕获子流程的输出。

另一个过程是你可以直接把>运算符放在命令中。因此，如果我们在运行命令时将所有内容都放在一个文件中，则不需要复制任何内容。

在这种情况下，不需要使用管道。您可以只使用system，它将运行命令并将输出放在该文件中。

int my_func(){
    char *command = (char *)"/usr/bin/my_script my_arg > /tmp/my_putput_file";
    system(command);
    printf("everything saved in my_output_file");
    return 0;
}

你可以阅读YoLinux教程:Fork, Exec和进程控制了解更多信息。