increment in a loop and keeping state - c

Question

gcc 4.4.4 c89
I have the following code and 2 structures that have to be filled.
I have 3 functions that will fill the handles for each of the devices.
However, the device_type structure will need to increment from where the last function finished.
For example:
load_resources() starts at 0 and finishes at 9
dev_types starts at 0 and finishes at 9
load_networks() starts at 0 and finishes at 9
dev_types starts at 10 and finishes at 19
load_controls() starts at 0 and finishes at 9
dev_types starts at 20 and finishes at 29
However, as I don't want to use a static or global variable is there any way I can increment a
value for this. So it will start where the last function finished.
Many thanks for any suggestions,
#define NUMBER_OF_DEVICES 10
#define NUMBER_OF_TYPES 3 /* resources
networks
controls */
int events(int evt);
int load_resources();
int load_networks();
int load_controls();
static struct device_table {
int resource_handle;
int network_handle;
int control_handle;
} dev_tbl[NUMBER_OF_DEVICES];
struct device_types {
size_t id;
int dev_handle;
int dev_type;
}dev_types[NUMBER_OF_DEVICES * NUMBER_OF_TYPES];
enum dev_name_types {RESOURCE, NETWORK, CONTROL};
/* Simulates the API calls, by returning a dummy handle */
int get_resources();
int get_networks();
int get_controls();
int main(void)
{
srand(time(NULL));
load_resources();
load_networks();
load_controls();
return 0;
}
int load_resources()
{
size_t i = 0;
for(i = 0; i < NUMBER_OF_DEVICES; i++) {
dev_tbl[i].resource_handle = get_resources();
printf("dev_tbl[i].resource_handle [ %d ]\n", dev_tbl[i].resource_handle);
dev_types[i].id = i;
dev_types[i].dev_handle = dev_tbl[i].resource_handle;
dev_types[i].dev_type = RESOURCE;
}
}
int load_networks()
{
size_t i = 0;
for(i = 0; i < NUMBER_OF_DEVICES; i++) {
dev_tbl[i].network_handle = get_networks();
printf("dev_tbl[i].network_handle [ %d ]\n", dev_tbl[i].network_handle);
dev_types[i].id = i;
dev_types[i].dev_handle = dev_tbl[i].network_handle;
dev_types[i].dev_type = NETWORK;
}
}
int load_controls()
{
size_t i = 0;
for(i = 0; i < NUMBER_OF_DEVICES; i++) {
dev_tbl[i].control_handle = get_controls();
printf("dev_tbl[i].control_handle [ %d ]\n", dev_tbl[i].control_handle);
dev_types[i].id = i;
dev_types[i].dev_handle = dev_tbl[i].control_handle;
dev_types[i].dev_type = CONTROL;
}
}

Answer 1

Why not change the prototypes to something like:
void load_resources(int*)
(they're not actually returning anything) then, in your main code, have:
int base = 0;
load_resources (&base);
load_networks (&base);
load_controls (&base);
Each function is then responsible for using and updating *base like this:
void load_resources (int *pBase) {
size_t i = 0;
for(i = 0; i < NUMBER_OF_DEVICES; i++, (*pBase)++) { // <-- see here!
dev_tbl[i].resource_handle = get_resources();
printf("dev_tbl[i].resource_handle [ %d ]\n", dev_tbl[i].resource_handle);
dev_types[*pBase].id = i;
dev_types[*pBase].dev_handle = dev_tbl[i].resource_handle;
dev_types[*pBase].dev_type = RESOURCE;
}
}

Answer 2

One option is to have each of your functions take the base index as a parameter, and returning the first available index:
int index = 0;
index = load_resources(index);
index = load_network(index);
// and so on
With this yout functions would look something like this:
int load_resources(int base_index)
{
size_t i = 0;
size_t index;
for(i = 0; i < NUMBER_OF_DEVICES; i++) {
index = base_index + i;
dev_tbl[index].resource_handle = get_resources();
//
}
return index + 1;
}
By the way, your functions do have int return types, but do not return anything.

Answer 3

Hold a pointer or index variable within the structure itself. It's an indicator for how far the structure has been filled up generally.

Answer 4

There are only two ways to persist data from one scope to the next - on the stack and on the heap. Since you have already ruled out any global variables here, that would require you to use stack variables, by passing in a parameter and returning a value, or passing in a pointer to a parameter.