在C ++中串联十六进制值

Question

I am having trouble concatenating two hex values in C++;

int virtAddr = (machine->mainMemory[ptrPhysicalAddr + 1] << 8) | (machine->mainMemory[ptrPhysicalAddr]);
int physAddr = currentThread->space->GetPhysicalAddress(virtAddr);

For machine->mainMemory[ptrPhysicalAddr + 1] , this yields 0x5 . For machine->mainMemory[ptrPhysicalAddr] , this yields 0x84 . I expect the result 0x584 . However, I am getting 0xffffff84 . I followed this question Concatenate hex numbers in C .

Answer 1

0x84 is -124 . It gets widened to (int)-124 before the bitwise-OR operation (integer promotion). And 0x00000500 | 0xFFFFFF84 0x00000500 | 0xFFFFFF84 is the result you got. Use an unsigned type to prevent sign-extension when widening.

intptr_t virtAddr = (uint8_t(machine->mainMemory[ptrPhysicalAddr + 1]) << 8)
                   | uint8_t(machine->mainMemory[ptrPhysicalAddr]);