Thread: subtle issue that i cant find

I need to make an argument vector to pass to execv()... I'm creating it like shown below, I've tested it so I know all my strings are getting null termininated etc... but any programs I execute with execv() complain they aren't getting their arguments.

Can anyone find the subtle thing wrong here?

Code:

	 
	 char* argv[MAX_ARGS] = { 0 }; // need this to pass to execv()
         string argument; 
	 stringstream ss;
	 ss << input;
	 ss >> command;
	 int i = 0; 
	 if ( command.size() != input.size() )  // were there arguments?
	 {
		 arguments = input.substr(command.size()+1);  // make an argument string.
		 while ( (ss >> argument) && (i < (MAX_ARGS-1)) ) // create argument vector.
		 { 
			 argv[i] = new char[argument.size()+1];    // allocate memory
			 memset(argv[i], '\0', argument.size()+1); // null it out
			 argument.copy(argv[i], argument.size());  // copy argument to argv
			 i++;
		 }
		 argv[i] = '\0'; // make last element null
	 }
	 /* child */
	execv((path+command).c_str(), argv);

I don't see anything obviously wrong - have you tried making a loop to print your "argv" array when you have parsed the arguments?

Minor nits:
You probably want:

Code:

		 argv[i] = NULL; // make last element null

instead of:

Code:

		 argv[i] = '\0'; // make last element null

Code:

			 memset(argv[i], '\0', argument.size()+1); // null it out
			 argument.copy(argv[i], argument.size());  // copy argument to argv

Setting the entire array to zero, then overwriting all but one byte with a string is a bit excessive. Perhaps this would work better:

Code:

			 argument.copy(argv[i], argument.size());  // copy argument to argv
			 argv[i][argument.size()+1] = '\0';

--
Mats

argv[0] should be a program name, are you setting it ok? I do not think so - you skippint the command

argv[i][argument.size()+1] = '\0';

Oh no! Remove +1 here

Originally Posted by vart

argv[0] should be a program name, are you setting it ok? I do not think so - you skippint the command

Good point, so it's probably not missing ALL the arguments, it's just getting one less than it expects, and failing due to that...

--
Mats

Originally Posted by vart

Oh no! Remove +1 here

Yes of course.

--
Mats