c++ - Pointer memory usage -

i may wrong on these facts correct me!

a pointer points memory address, if went memory address find byte ? pointer points lowest address of memory segment points too, if points 8 byte memory segment, starts @ 0x0 , ends @ 0x7, point 0x0 ?

how pointer know size of memory points at? if pointer points segment of memory 128 bytes in size , pointer cast different type, happens size of memory segment?

how pointer know size of memory points @ ?

it doesn't.

so if pointer points segment of memory 128 bytes in size , pointer cast different type, happens size of memory segment ?

the memory's still there, since cast away information had object residing there, well, y'know. that's it. don't know.

that's why people use sizeof when aliasing objects through char* @ underlying bytes:

std::ofstream os("some-binary-file"); const double d = 0.1234;  os.write((char*)&d, sizeof(double)); //                  ^^^^^^^^^^^^^^ //  // otherwise os.write has no way of knowing how write 

of course, if chuck around double*, every piece of code using pointer assume points 1 or more "blocks" of memory precisely sizeof(double) bytes wide. if doesn't, that's fault.

tl;dr: telling program how many pointee bytes has work your responsibility.