Writing/Reading struct w/ dynamic array through pipe in C
- by anrui
I have a struct with a dynamic array inside of it:
struct mystruct{
int count;
int *arr;
}mystruct_t;
and I want to pass this struct down a pipe in C and around a ring of processes. When I alter the value of count in each process, it is changed correctly. My problem is with the dynamic array.
I am allocating the array as such:
mystruct_t x;
x.arr = malloc( howManyItemsDoINeedToStore * sizeof( int ) );
Each process should read from the pipe, do something to that array, and then write it to another pipe. The ring is set up correctly; there's no problem there. My problem is that all of the processes, except the first one, are not getting a correct copy of the array. I initialize all of the values to, say, 10 in the first process; however, they all show up as 0 in the subsequent ones.
for( j = 0; j < howManyItemsDoINeedToStore; j++ ){
x.arr[j] = 10;
}
Initally: 10 10 10 10 10
After Proc 1: 9 10 10 10 15
After Proc 2: 0 0 0 0 0
After Proc 3: 0 0 0 0 0
After Proc 4: 0 0 0 0 0
After Proc 5: 0 0 0 0 0
After Proc 1: 9 10 10 10 15
After Proc 2: 0 0 0 0 0
After Proc 3: 0 0 0 0 0
After Proc 4: 0 0 0 0 0
After Proc 5: 0 0 0 0 0
Now, if I alter my code to, say,
struct mystruct{
int count;
int arr[10];
}mystruct_t;
everything is passed correctly down the pipe, no problem. I am using READ and WRITE, in C:
write( STDOUT_FILENO, &x, sizeof( mystruct_t ) );
read( STDIN_FILENO, &x, sizeof( mystruct_t ) );
Any help would be appreciated. Thanks in advance!
