Configuration of a module's data sending - c

Question

I want to configure (module A) to send certain data to (module B) at certain slots of time.
(Module B) should send these configuration to (module A) during initialization.
The data is:
struct _data
{
int temp;
int velocity;
int time;
}
For example, (module A) should send 'temp' at first slot, then 'temp & velocity' at second slot, then 'time' at third slot .... etc
I am thinking about making making "configuration flags" structure:
struct _configuration
{
int temp_flag;
int time_flag;
int velocity_flag;
}
Then making an array of this structures:
struct _configuration arr[NUMBER_OF_SLOTS];
and configure using this array:
arr[0].temp_flag = 1;
arr[0].velocity_flag = 0;
arr[0].time_flag = 0;
arr[1].temp_flag = 1;
arr[1].velocity_flag = 1;
arr[1].time_flag = 0;
arr[2].temp_flag = 0;
arr[2].velocity_flag = 0;
arr[2].time_flag = 1;
.... etc
But I am not very happy with this approach ... does anyone has a better way or algorithm to do this task ?
Many thanks in advance

Answer 1

One of the many possible solutions is bitmasks (very popular in computer graphics). As you know, every number can be represented as sequence of 0 and 1, so they can be the flags that mean something. It's quite simple to use them in such way because we have bitwise operations. And there is no need to create some configuration structures.
const int USE_TEMP = 1 << 0; // 01
const int USE_VELOCITY = 1 << 1; // 010
const int USE_TIME = 1 << 2; // 0100
// ...
// you have 32 free-to-use bits
const int USE_ALL = 0111; // just for fun
struct _data {
int temp;
int velocity;
int time;
}
And it bring us to
int arr[NUMBER_OF_SLOTS];
arr[0] = USE_TEMP;
arr[1] = USE_TEMP | USE_VELOCITY;
arr[2] = USE_TIME;
Looks better, isn't it?
Checking values
When you need to check whether some of the parameters included in configuration, it's very simple
if( arr[i] & USE_TEMP ) {
// do smth with temp, it's included
}
or this way
int expected_flags = USE_TIME | USE_VELOCITY;
if( arr[i] & expected_flags == expected_flags ) {
// time and velocity enabled
}
or even declare special function (or scary macro) to check whether some parameters are in your config
bool check(int config, int flags) {
return config & flags == flags;
}
Changing configurations
What if you need to delete/add parameters?
int some_conf = USE_TEMP | USE_VELOCITY;
Simple way
// delete
if( check(some_conf, USE_VELOCITY) )
some_conf -= USE_VELOCITY; // <--- dangerous without if( )
// add
if( !check(some_conf, USE_TIME) )
some_conf += USE_TIME; // <--- dangerous without if( )
Safety way
// delete
some_conf &= ~USE_VELOCITY;
// add
some_conf |= USE_TIME;