problem with argv / argc

[geojameson]

Hello, I am working on an assignment for my 'Operating Systems' class. Our first assignment deals with creating processes using the fork(). I have most of the program already written (I can PM everything I have written if it helps) but I am getting stuck on trying to add a 0 to the end of the argv[ ] array. Whenever I use an even number on the command line like "master 1 2 3 4" it works fine because there is an even # of values to add but when there is an odd # is when I am getting segmentation faults (like "master 1 2 3").

Here is the part of my code I believe is causing problem:

    // Trying to add a 0 to the array if theres an odd # of values
    // But its core dumping when it goes through this statement
      if(argc % 2 == 0)
      {
    argc = argc + 1;
    argv[argc] = argv[argc-1];
    sprintf(argv[argc-1], "%d", 0);
      }
 

Heres the assignment I am working on:

You will write a program that uses multiple processes to compute the sum of a set of (small) positive integers.

There are two types of processes for this homework:

I). A set of "slaves" processes: Each slave process gets two small integers from its argv, computes its sum and returns the result using the exit system call. So, a slave process is created for every sum.

II) A "master" process: This process is responsible for creating the slave processes, and coordinating the computation. Note that all the computation is done by the "slave" processes. All the numbers are provided in the command line argv. The master process also set a timer at the start of computation to 3 seconds. If the computation has not been finished by this time, the master process kills all the slaves and then exits. You should print an appropriate message(s) in this case. Note that the master process may have to create multiple sets of slave processes. For example, if there are 8 numbers to be added, then the master process will first create 4 slaves and get the result from them. At this point there are 4 numbers, and it creates 2.

slaves. Finally one slave is created to compute the overall sum. To make it simpler, if the number of integers to add is odd, the master adds a 0 to the list of numbers. This may happen at any step during the computation. The code for master process should be compiled separately and its executable code should be called master. The executable code for the slave process should be called slave. So, to compute the sum of the numbers 1 through 7, the command line will look like

master 1 2 3 4 5 6 7

Since the results are passed around by exit system call, keep the numbers small (single digit). Each slave process prints its process id, its operands, and their sum. Each time the master gets a result from a slave, it prints the pid of the slave and the partial sum.

Hand in a hard copy and demo it on Eagle in class. (sample runs).

[Motoma]

Hello, I am working on an assignment for my 'Operating Systems' class. Our first assignment deals with creating processes using the fork(). I have most of the program already written (I can PM everything I have written if it helps) but I am getting stuck on trying to add a 0 to the end of the argv[ ] array. Whenever I use an even number on the command line like "master 1 2 3 4" it works fine because there is an even # of values to add but when there is an odd # is when I am getting segmentation faults (like "master 1 2 3").

Here is the part of my code I believe is causing problem:

    // Trying to add a 0 to the array if theres an odd # of values
    // But its core dumping when it goes through this statement
      if(argc % 2 == 0)
      {
    argc = argc + 1;
    argv[argc] = argv[argc-1];
    sprintf(argv[argc-1], "%d", 0);
      }
 

Heres the assignment I am working on:

You are writing to a segment of memory that has not necessarily been allocated to your program. You are quire likely overwriting necessary data, you are instigating a buffer overflow with this code.
Rather than appending to the fixed length buffer argv, why not create your own copy of the data, which has a 0 appended if needed.

[Motoma]

I have moved this thread to the C/C++ forum, because this question is not related to Linux.

[soumya0406]

Hi,
I need to do the same program now.Can u please send me the complete program.It will be a great help.

[JosAH]

Hi,
I need to do the same program now.Can u please send me the complete program.It will be a great help.

I sincerely hope that the OP isn't reading nor listening to your pathetic begging.
It won't be any help because *you* need to design and implement this program,
you're not supposed to cheat. Now go and start working on it.

Jos (moderator)