can the Pointer have value?? so In which case is it used
int num=100;
int* iptr=NULL;
iptr=reinterpret_cast<int*>(num);
printf("%d \n",num);
printf("%d \n",num);
result 100 100
1 Answer
- Mappings between pointers and integers are implementation-defined.
- Conversion of an integer to a pointer using
reinterpret_castwill not be a safely-derived pointer value except under certain conditions. Those conditions are not met in your example.
Citation from CPP draft (N4713):
8.5.1.10 Reinterpret cast
...
6. A value of integral type or enumeration type can be explicitly converted to a pointer. A pointer converted to an integer of sufficient size (if any such exists on the implementation) and back to the same pointer type will have its original value; mappings between pointers and integers are otherwise implementation-defined. [ Note: Except as described in 6.6.4.4.3, the result of such a conversion will not be a safely-derived pointer value. —end note ]
The conditions for Safely-derived pointers.
6.6.4.4.3 Safely-derived pointers
...
2 A pointer value is a safely-derived pointer to a dynamic object only if it has an object pointer type and it is one of the following:
(2.1) — the value returned by a call to the C++ standard library implementation of ::operator new(std::size_t) or ::operator new(std::size_t, std::align_val_t);
(2.2) — the result of taking the address of an object (or one of its subobjects) designated by an lvalue resulting from indirection through a safely-derived pointer value;
(2.3) — the result of well-defined pointer arithmetic using a safely-derived pointer value;
(2.4) — the result of a well-defined pointer conversion of a safely-derived pointer value;
(2.5) — the result of a reinterpret_cast of a safely-derived pointer value;
(2.6) — the result of a reinterpret_cast of an integer representation of a safely-derived pointer value;
(2.7) — the value of an object whose value was copied from a traceable pointer object, where at the time of the copy the source object contained a copy of a safely-derived pointer value.
iptr=reinterpret_cast<int*>(num);makes no C sense; C tag deleted.numand then prints the value twice. No pointers needed to understand whats going on, but it bet you worry about those two lines inbetween (that currently have zero effect on the output of your code)