Thread: Calling external program and reading its output.

  1. 10-17-2007 #1
    Dragoon_42
    Dragoon_42 is offline
    Slime Dragoon_42's Avatar
    Join Date
    Feb 2003
    Location
    Vancouver
    Posts
    90

    Question Calling external program and reading its output.

    I have a program that gathers data from a machine and outputs it to the command line from which it is called. I would like to write a program that calls the other program, reads its output, and writes that to a file. Here's an example of the output from the program:

    Polling slave ...
    [123]: 112
    [124]: 101
    [125]: 96
    [126]: 101
    [127]: 187
    [128]: 194
    [129]: 171
    [130]: 177
    [131]: -80
    [132]: 0
    [133]: 0
    [134]: 69
    [135]: 0
    [136]: 1016
    [137]: 0
    [138]: 2555
    [139]: 0
    [140]: 2437
    [141]: 108

    So I know I can use system() to call the program, but that only returns an integer when I need all that garbage above. Could someone point me in the right direction?
  2. 10-17-2007 #2
    dwks
    dwks is offline
    Frequently Quite Prolix dwks's Avatar
    Join Date
    Apr 2005
    Location
    Canada
    Posts
    8,057
    Just redirect the output of that program into a file.
    Code:
    program > outputfile
    This can be done from within system(), or even from the command line. It's reasonably portable, as well, though it assumes that you have write permissions.

    Alternatively, and less portably but more conveniently, you could use popen(), if you wanted to process that data afterwards.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell

    Other boards: DaniWeb, TPS
    Unofficial Wiki FAQ: cpwiki.sf.net

    My website: http://dwks.theprogrammingsite.com/
    Projects: codeform, xuni, atlantis, nort, etc.
  3. 10-17-2007 #3
    matsp
    matsp is offline
    Kernel hacker
    Join Date
    Jul 2007
    Location
    Farncombe, Surrey, England
    Posts
    15,677
    popen() doesn't exist in Windows (from MS CRT at least), but fortunatley there is a replacement called _popen() that apparently does similar enough a functionality to be perfect replacement. Using something like
    Code:
    #define popen _popen
    should make it work.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.
  4. 10-18-2007 #4
    Dragoon_42
    Dragoon_42 is offline
    Slime Dragoon_42's Avatar
    Join Date
    Feb 2003
    Location
    Vancouver
    Posts
    90
    I used the
    Code:
    program > outputFile
    suggestion and it worked just fine. Thanks all!
« Previous Thread | Next Thread »
Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Segmentation fault ith g_type_check_class_cast () from /usr/lib/libgobject-2.0.so.0
    By lehe in forum Game Programming
    Replies: 7
    Last Post: 02-02-2009, 07:27 AM
  2. Client-server system with input from separate program
    By robot-ic in forum Networking/Device Communication
    Replies: 3
    Last Post: 01-16-2009, 03:30 PM
  3. calling an external program + capture output?
    By cyberfish in forum C++ Programming
    Replies: 4
    Last Post: 03-21-2008, 12:49 AM
  4. program terminated by signal SEGV, ONLY on a certain server
    By pncuong83 in forum C Programming
    Replies: 2
    Last Post: 01-28-2008, 03:07 AM
  5. airport Log program using 3D linked List : problem reading from file
    By gemini_shooter in forum C Programming
    Replies: 3
    Last Post: 03-04-2005, 02:46 PM