Capture output from system command

[niskin]

I am running a system command and I need to capture the output so that, if the command has done what it is meant to, the program does something different. If I do this:

int i;
i=system("cd C:\\Dave\\C-programming\\Password Cracker\\ & ftp -s:ftpscript.txt ftp.collateraldesign.co.uk");
printf ("The value returned was: %d.\n",i);

The value returned is 0. However, I want to know if there was an error logging on, how can I know whether the command was successful or not?

[weaknessforcats]

The system() command passes your argument to the correct command interpreter and returns whatever the command inrterpreter returns.

You should be able to capture the return value from system().

Check your docs.

[niskin]

Ok, the only problem is it always returns 0 if the command is carried out successfully, but I would prefer it to say something like "connection successful/unsuccessful", at least something to distinguish between success and failure.

[weaknessforcats]

Isn't the 0 enough for success and !0 is failure??

Otherwise, you will get into a soggy area of return codes, errnos and stuff like that which may not be consistent from one command interpreter to the next.

More than this an you may have to write the code to process the request you send to the system() command yourself.

[niskin]

Ok, is there an alternative to the system command? I have heard of popen and exec but I am not clear on them.

[weaknessforcats]

popen creates a pipe. You run your command as a spawned thread and the output of the thread goes into one end of the pipe in memory leaving you with the ability to read the output from the pipe as though it were in a disc file.

You might check this one out.

I'm not sure what exec is.

Here is a link to the Microsoft docs for popen.

[niskin]

Cheers, that's really helpful.