Getting segmentation fault on master/slave

Question

can anyone explain to me why I am getting a segmentation fault on this code? I have been trying to figure it out and have come up empty on various searches. When I run the code without calling main(argc, argv) it runs. Slave only transforms the 2 numbers in argv to ints then returns them. Thanks.

#include <stdio.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

int main(int argc, char* argv[])
{
    int i;
    int* sums;
    sums[argc];
    pid_t cpid;
    int status;
    char* args[10];
    int count = 1;

    for(i = 0; i < (argc / 2); i++) {
        cpid = fork();

        if(cpid == 0) {
            args[1] = argv[count];
            args[2] = argv[count + 1];
            execvp("./slave", args);
        } else {
            waitpid(cpid, &status, 0);
            sums[i] = WEXITSTATUS(status);

            printf("Child returned the number %d\n", sums[i]);
            sprintf(argv[i+1], "%d", sums[i]);
        }
        count += 2;
    }

    if(sums[0] == 0) {
        printf("done\n");
    } else {
        main(argc/2, args);
    }
}

Answer 1

first problem is that you did not allocate any memory for sums and sums[i] accesses a trashy location. do this:

 int sums[argc];

Secondly, for execvp function argument array has to have 1. [0] -- a legal string. 2. the last element [3] must be NULL

       args[0] = "some-execution-file-name";
       args[1] = argv[count];
       args[2] = argv[count + 1];
       args[3] = NULL;

Otherwise the function has no idea about the size of the array and slave can die trying to read element [0].