I know there’s an old saying when you want to indicate this specific pointer doesn’t point to anything it should be set to NULL(actually 0), but I’m wondering isn’t there actually a physical part of memory with the address of NULL(0) ?
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I know there’s an old saying when you want to indicate this specific pointer doesn’t point to anything it should be set to NULL(actually 0), but I’m wondering isn’t there actually a physical part of memory with the address of NULL(0) ?
There is always a physical address of 0 (but it may not necessarily map onto physical RAM), but on a typical platform any accesses will typically be performed in a virtual address space (as jweyrich points out below, you can use
mmapand so on to directly map the physical address space), so any attempt to read/write to address 0 will raise an exception of some kind.On simpler processors (think microcontrollers and so on), there may be no such protection, so if you attempt to write to address 0, there’ll be nothing to catch you.
Note also that a null pointer doesn’t necessarily have to point at address 0; the only guarantee is that it will compare equal to integer value
0.