Basic python Tutorial-examples of input and output operations for other programs using the popen function

Source: Internet
Author: User
The popen function allows a program to start another program as a new process and transmit data to it or receive data through it. the following example shows how to use the function.

1.1 Function prototype:

The code is as follows:


# Include
FILE * popen (const char * command, const char * open_mode );

1.2 Description

The popen function allows a program to start another program as a new process and transmit data to it or receive data through it. The command string is the program name to run and the corresponding parameter (such as ls or ls-l). openmode must be r or w. If it is r, the output of the called program can be used by the program calling it; if it is w, the caller can use fwrite to send data to the called program as its input in the standard input stream.

2. test program preparation

Prepare two simple programs for the test below.

2.1 output test program

The code is as follows:


// OutputTest. c
# Include

Int main ()
{
Printf ("Just a test! \ N ");
Return 0;
}

The main function is to output a string to the standard output device for the following program to test.

2.2 enter the test program

The code is as follows:


// InputTest. c
# Include

Int main ()
{
Char buf [1024] = {0 };
Scanf ("% s", buf );
Printf ("your input: % s \ n", buf );
Return 0;
}

It is mainly used to input and output strings from the standard input device for testing in the following program.

3. popen operation example (C code)

3.1 obtain program output

Use the outputTest program for testing. the code is as follows:

The code is as follows:


# Include
# Include
# Include
# Include

Int main ()
{
FILE * read_fp;
Char buffer [BUFSIZ + 1];
Int chars_read;
Memset (buffer, '\ 0', sizeof (buffer ));
Read_fp = popen ("./outputTest", "r ");
If (read_fp! = NULL)
{
Chars_read = fread (buffer, sizeof (char), BUFSIZ, read_fp );
If (chars_read> 0)
{
Printf ("Output was: \ n % s \ nDone \ n", buffer );
}
Pclose (read_fp );
Exit (EXIT_SUCCESS );
}
Exit (EXIT_FAILURE );
}

The running effect is as follows:


Here, the r parameter is used to obtain the output of the called program.

3.2 pass parameters to other programs

Use inputTest for testing. the code is as follows:

The code is as follows:


# Include
# Include
# Include
# Include

Int main ()
{
FILE * write_fp;
Char buffer [BUFSIZ + 1];

Sprintf (buffer, "Once... \ n ");
Write_fp = popen ("./inputTest", "w ");
If (write_fp! = NULL)
{
Fwrite (buffer, sizeof (char), strlen (buffer), write_fp );
Pclose (write_fp );
Exit (EXIT_SUCCESS );
}
Exit (EXIT_FAILURE );
}

The running effect is as follows:

Here, the w parameter is used to transmit parameters to the called program.

4. poepn operation example (python code)

In fact, python can also be used like this.

4.1 obtain program output

The outputTest program mentioned above is used as an example. the code is as follows:

The code is as follows:


#! /Usr/bin/python

Import OS
# Var = OS. popen ('ls-L'). read ()
Var = OS. popen ('./outputtest'). read ()
Print var

The running effect is as follows:

4.2 pass parameters to other programs

The inputTest program mentioned above is used as an example. the code is as follows:

The code is as follows:


#! /Usr/bin/python

Import OS
OS. popen ('./inputtest', 'w'). write ("test ")

The running effect is as follows:

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.