The most efficient way to use different structure elements in a function?

Question

I am writing for a very limited resource embedded processor. I have a structure that captures the time series of events, and I would like to use the same graphic display function for different values ​​of different types. Something like (very stripped down, do not sweat uninitialized values, etc.):

#define GRAPH_ONE 1 #define GRAPH_TWO 2 struct _event_t { unsigned long timestamp; int sensorOne; float sensorTwo; } typedef struct _event_t event_t; event_t[10] MyEvents; void GraphSensor(byte graphType) { for (unsigned int i = 0; i < 9; i++) { // Get minimum value from series if (MyEvents[i].?????) ... } } 

How can I use my function for different members of the structure? I can see this with a ton of switch (graphType) statements, but it's pretty ugly. There can easily be 8 or 10 members of the structure. I could move all these functions to a separate function and make each data access bit this function, always returning a float (which should be OK for my graph). Finally, I can convert to C ++ classes, which opens up other tools.

None of them are feeling well. Is there a better approach, preferably very light?

Answer 1

You can wrap the accessory that you need in the function and pass it to the function, which moves the array and aggregates the results. for instance

 float getSensor1(const event_t* t) { return t->sensorOne; } float getSensor2(const event_t* t) { return t->sensorTwo; } void GraphSensor(float (*accessor)(const event_t*)) { // Get minimum value from series float min_value = MAX_FLOAT; for (unsigned int i = 0; i < 9; i++) { float x = accessor(MyEvents + i); if (x < min_value) min_value = x; } } /* later on . . . */ GraphSensor(getSensor1); GraphSensor(getsensor2); 

You basically disconnect data access from operations on it and homogenize it all to floating ones. The aggregation operation can also be encapsulated in a function. But this is approaching a smaller map. :)

Answer 2

You can change the structure to an array that uses, possibly, all floats. Thus, data processing is completely homogeneous.

 #define N_SENSORS 12 #define N_EVENTS 10 float MyEvents [N_EVENTS] [N_SENSORS]; void GraphSensor(byte graphType) { float min = 1e38; for (unsigned int i = 0; i < N_EVENTS; i++) { // Get minimum value from series if (MyEvents[i][graphType] < min) min = MyEvents[i][graphType]; } } 

Perhaps the timestamp can also be in element 0, possibly using tables: the integer part is days from 1970 or 1900, and the fractional part is part of the day (so noon = .5).