Const (computer programming): Difference between revisions

Revision as of 18:24, 24 October 2005

Revision as of 18:29, 24 October 2005

Line 129:

const volatile int & hardwareRegister = *reinterpret_cast<int*>(0x8000);

hardwareRegister = 5; // Error! Cannot write to a const ___location

int currentValue = hardwareRegister; // Read the memory ___location

int newValue = hardwareRegister; // Read it again

hardwareRegister = 5; // Error! Cannot write to a const ___location

Because <code>hardwareRegister</code> is volatile, there is no guarantee that it will hold the same value on two successive reads even though the programmer cannot modify it. The semantics here indicate that the register's value is read-only but not necessarily unchanging.

Line 139:

// Set up a pointer to a read-only memory-mapped register that

// contains a memory address for us to deferencedereference

const int * volatile const tableLookup = reinterpret_cast<int*>(0x8004);

int currentTableValue = *tableLookup; // DeferenceDereference the memory ___location

int newTableValue = *tableLookup; // DeferenceDereference it again

tableLookup = &currentTableValue; // Error! Cannot modify a const pointer