Question

I have a C program which has always used hard coded define statements for a few settings. Example…

#define TRIGGER_TIMEOUT 50000

This has worked just fine. Now, this setting is to become adjustable. Example…

g_ulTriggerTimeout = ReadEEPROM(TRIGGER_TIMEOUT_OFFSET);

If persistent storage is detected (EEPROM) then the value will be read in and used. So, my safe literal value is now at risk of being corrupted (inadvertently written changed). I need to make this variable a constant, however I also need to read in the initial values from EEPROM. How is this scenario typically solved?

Answer 1

This is IMHO one of those cases where bending the rules is ok.

const int g_ulTriggerTimeout; //declare somewhere making sure it is in a writable section (see comment below from undur)

/* later */

//just for this assignment make it modifiable
*((int*) &g_ulTriggerTimeout) = ReadEEPROM(TRIGGER_TIMEOUT_OFFSET);