Asked  6 Months ago    Answers:  5   Viewed   52 times

I've got a utility that outputs a list of files required by a game. How can I run that utility within a C program and grab its output so I can act on it within the same program?

UPDATE: Good call on the lack of information. The utility spits out a series of strings, and this is supposed to be portable across Mac/Windows/Linux. Please note, I'm looking for a programmatic way to execute the utility and retain its output (which goes to stdout).

 Answers

16

For simple problems in Unix-ish environments try popen().

From the man page:

The popen() function opens a process by creating a pipe, forking and invoking the shell.

If you use the read mode this is exactly what you asked for. I don't know if it is implemented in Windows.

For more complicated problems you want to look up inter-process communication.

Tuesday, June 1, 2021
 
PLPeeters
answered 6 Months ago
35

You can use the backtics to execute your external program and capture its stdout and stderr.

By default the backticks discard the stderr and return only the stdout of the external program.So

$output = `cmd`;

Will capture the stdout of the program cmd and discard stderr.

To capture only stderr you can use the shell's file descriptors as:

$output = `cmd 2>&1 1>/dev/null`;

To capture both stdout and stderr you can do:

$output = `cmd 2>&1`;

Using the above you'll not be able to differenciate stderr from stdout. To separte stdout from stderr can redirect both to a separate file and read the files:

`cmd 1>stdout.txt 2>stderr.txt`;
Thursday, June 24, 2021
 
seaders
answered 6 Months ago
10

Here's what I gather from your question, and your comments:

  1. You want to know if it is possible to execute an executable embedded into your program, without extracting it to disk first
  2. Your program is a .NET program
  3. The executable you want to execute is not a .NET program

The answer to that is: yes

However, the answer to that is also it is very, very, hard

What you have to do is, and note that I do not know all the details about this since I don't do this, but anyway:

  1. Load the executable code into memory
  2. Remap all addresses in the binary image so that they're correct in relation to the base address you loaded the executable at
  3. Possibly load external references, ie. other DLL's that executable need
  4. Remap the addresses of those references
  5. Possibly load references needed by the just loaded referenced DLL's
  6. Remape those dll's
  7. Repeat 3 through 6 until done
  8. Call the code

I'm assuming your question is "can I do 1 and 8", and the answer to that is no.

Friday, July 23, 2021
 
brombeer
answered 5 Months ago
11

You cannot do this. Linux create new process by sequential call to fork() and exec(). No other way of process creation exists.

But fork() itself is quite efficient. It uses Copy-on-Write for child process, so fork() not copy memory until it is really needed. So, if you call exec() right after fork() your system won't eat too much memory.

UPD. I lie to you saying about process creation. In fact, there is clone() call which fork() uses internally. This call provides more control over process creation, but it can be complicated to use. Read man 2 fork and man 2 clone for more information.

Saturday, July 31, 2021
 
cyber_truite
answered 4 Months ago
85

You started cmd.exe, then cmd.exe starts child process ping.exe. To kill ping.exe you can kill all process hierarchy. For example with WMI(add System.Management reference):

private static void KillProcessAndChildrens(int pid)
{
    ManagementObjectSearcher processSearcher = new ManagementObjectSearcher
      ("Select * From Win32_Process Where ParentProcessID=" + pid);
    ManagementObjectCollection processCollection = processSearcher.Get();

    try
    {
        Process proc = Process.GetProcessById(pid);
        if (!proc.HasExited) proc.Kill();
    }
    catch (ArgumentException)
    {
        // Process already exited.
    }

    if (processCollection != null)
    {
        foreach (ManagementObject mo in processCollection)
        {
            KillProcessAndChildrens(Convert.ToInt32(mo["ProcessID"])); //kill child processes(also kills childrens of childrens etc.)
        }
    }
}
Monday, September 6, 2021
 
St.Antario
answered 3 Months ago
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