error in coping argv[] to int array in c

Question

# include <stdio.h>
# include <stdlib.h>
# include <stddef.h>
# include <sys/types.h>
# include <sys/ipc.h>
# include <sys/shm.h>
# include <sys/sem.h>
# include <unistd.h>
# include <time.h>
# include <math.h>

int main(int argc, const char* argv[])
{
  int i,j,x,shM, *shmPtr;
 int *array_pid, *apotelesma, loops,y,N;
int *array1; 
double  a,b,temp;





shM=shmget(3002,sizeof(int),IPC_CREAT|0600);
shmPtr=(shM,0,0);


 array1=(int*)malloc((argc-2)*sizeof(int));

 if(array1==NULL)
 printf("error in array1");

for (i=0;i<=(argc-2);i++)
{
 array1[i]=atoi(argv[i]);

}

N=argc;
loops=atoi(argv[argc-1]);
array_pid=(int*)malloc(N*sizeof(int));

if (array_pid==NULL)
printf("error in array_pid");

apotelesma=(int*)malloc(N*sizeof(int));

if (apotelesma==NULL)
printf("error in apotelesma");

j=fork();

if (j>0)
{
 array_pid[i]=j;


for (i=0;i<loops;i++)
{

srand(time(NULL));

if (i>0)
apotelesma[i]=*shmPtr;

y=(rand()%(argc-2));

array1[y]=*shmPtr;
printf("y=%d apotelesma=%d",y,apotelesma[i]);



}




*shmPtr=-1;





for (i=0;i<N;i++)
wait();


shmdt(shmPtr);
shmctl(shM,0,IPC_RMID);

exit(0);
}

else  //child
{
while(1)
{

  x=*shmPtr;
  if(x<0)
{

 exit(0);
}
 a=rand();
 b=rand();
 temp=(pow((a-x/2),2)+pow((b-x/2),2));
 temp=sqrt(temp);
 if (temp<=x/2)
      *shmPtr=1;
     else
         *shmPtr=0;


    }


}

}

i'm posting again the whole code cause i am not really sure where the segmentation fault is. i think now that it might be shared memory that causes the problem. thanks for the information about counting argv.

Answer 1

For an array of length argc-2, only indexing of 0 to argc - 3 are valid. So this

for (i=1;i<=(argc-2);i++)

is wrong because you are accessing array[argc - 2]. It should be:

for (i = 0; i < argc - 2; i++)

Note that there might be other errors causing the segmentation fault because you didn't provide how you call the program.

It's better to be defensive to process command line arguments. (i.e, check the validity of argc, etc).

Answer 2

It is always better to check the argc value before going ahead when you pass command line arguments.

if(argc != /* num of arguments */)
return;

for (i=1;i<=(argc-2);i++)

This is wrong.

It has to be

for (i=0;i<argc-2;i++)