我正在寻找一种方法来获得命令的输出,当它从c++程序中运行时。我已经看到了使用system()函数,但它只会执行一个命令。以下是我正在寻找的一个例子:

std::string result = system("./some_command");

我需要运行任意命令并获得其输出。我在boost.org上找过了,但是我还没有找到任何能满足我需要的东西。


当前回答

获得stdout和stderr(也写入stdin,这里没有显示)与我的pstreams头很容易,它定义了iostream类的工作方式像popen:

#include <pstream.h>
#include <string>
#include <iostream>

int main()
{
  // run a process and create a streambuf that reads its stdout and stderr
  redi::ipstream proc("./some_command", redi::pstreams::pstdout | redi::pstreams::pstderr);
  std::string line;
  // read child's stdout
  while (std::getline(proc.out(), line))
    std::cout << "stdout: " << line << '\n';
  // if reading stdout stopped at EOF then reset the state:
  if (proc.eof() && proc.fail())
    proc.clear();
  // read child's stderr
  while (std::getline(proc.err(), line))
    std::cout << "stderr: " << line << '\n';
} 

其他回答

请注意,您可以通过将输出重定向到文件,然后读取它来获得输出

在std::system的文档中有显示

你可以通过调用WEXITSTATUS宏来接收退出码。

    int status = std::system("ls -l >test.txt"); // execute the UNIX command "ls -l >test.txt"
    std::cout << std::ifstream("test.txt").rdbuf();
    std::cout << "Exit code: " << WEXITSTATUS(status) << std::endl;

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

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;
}

获得stdout和stderr(也写入stdin,这里没有显示)与我的pstreams头很容易,它定义了iostream类的工作方式像popen:

#include <pstream.h>
#include <string>
#include <iostream>

int main()
{
  // run a process and create a streambuf that reads its stdout and stderr
  redi::ipstream proc("./some_command", redi::pstreams::pstdout | redi::pstreams::pstderr);
  std::string line;
  // read child's stdout
  while (std::getline(proc.out(), line))
    std::cout << "stdout: " << line << '\n';
  // if reading stdout stopped at EOF then reset the state:
  if (proc.eof() && proc.fail())
    proc.clear();
  // read child's stderr
  while (std::getline(proc.err(), line))
    std::cout << "stderr: " << line << '\n';
} 

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