How do I take the output of one program and use it

问题:

I have a program that takes the counts of experiments as command string argument and outputs the sequence of floating numbers. Example: im_7.exe 10 10.41 13.33 8.806 14.95 15.55 13.88 10.13 12.22 9.09 10.45

So, i need to call this program in my program and analyze this sequence of numbers.

回答1:

If your are on windows then you need to do the following

1. Create a Pipe1 using CreatePipe api of windows. Use this pipe for reading data from STDOUT of the child process.
2. Create a Pipe2 the same way and use that pipe for writing data to the STDIN of the child process.
3. Create the child process and in the startup info provide these handles and inherit the handles from the parent process. Also pass the cmd line arguments.
4. Close the write end of Pipe1 and read end of Pipe2.
5. In your case you are not writing anything into the child process input. You can straight away read the data from the child process output by reading from the Pipe1.

For a sample have a look at the following link. http://msdn.microsoft.com/en-us/library/ms682499%28VS.85%29.aspx

Hope this is what you are looking for.

回答2:

Data that one program prints to standard output (std::cout in C++) can be piped to the standard input (std::cin) of another program. The specifics of how the two programs are connected depends on the environment (specifically operating system and shell).

回答3:

You can create a class that holds your data (with >> and << overloads)

include <iostream>
#include <iterator>
#include <vector>
class MyData
{
public:
  friend 
  std::istream& 
  operator>>(std::istream& in, MyData& data)
  { 
    in >> data.size ;
    data.m_data.resize(data.size);
    std::copy( 
          std::istream_iterator<float>(in), 
          std::istream_iterator<float>( ),
          data.m_data.begin()
           );
  }
  friend
  std::ostream&
  operator<<(std::ostream& out, MyData& data)
  { 
    out<<  data.size << " ";
    for(size_t i=0;i<data.size;++i){
      out<< data.m_data[i] <<" ";
    }
    return out;
  }
private:
  int size;
  std::vector<float> m_data;
};

And then you can call it like so

int
main  (int ac, char **av)
{
  MyData d;
  std::cin>>d; //input one set of data;

  //test
  std::cout<<d;

  //get multiple data files
  std::vector<MyData> buffer;

   std::copy( 
            std::istream_iterator<MyData>(std::cin), 
            std::istream_iterator<MyData>( ),
        std::back_inserter(buffer)); // copies all data into buffer

}

On Linux the test pipe can be formed like so:

echo "4 1.1 2.2 3.3 4.4" | ./a.out

Not sure how to do pipes on Windows though...