reinterpret_cast Operator
The latest version of this topic can be found at reinterpret_cast Operator.
Allows any pointer to be converted into any other pointer type. Also allows any integral type to be converted into any pointer type and vice versa.
Syntax
reinterpret_cast < type-id > ( expression )
Remarks
Misuse of the reinterpret_cast operator can easily be unsafe. Unless the desired conversion is inherently low-level, you should use one of the other cast operators.
The reinterpret_cast operator can be used for conversions such as char* to int*, or One_class* to Unrelated_class*, which are inherently unsafe.
The result of a reinterpret_cast cannot safely be used for anything other than being cast back to its original type. Other uses are, at best, nonportable.
The reinterpret_cast operator cannot cast away the const, volatile, or __unaligned attributes. See const_cast Operator for information on removing these attributes.
The reinterpret_cast operator converts a null pointer value to the null pointer value of the destination type.
One practical use of reinterpret_cast is in a hash function, which maps a value to an index in such a way that two distinct values rarely end up with the same index.
#include <iostream>
using namespace std;
// Returns a hash code based on an address
unsigned short Hash( void *p ) {
unsigned int val = reinterpret_cast<unsigned int>( p );
return ( unsigned short )( val ^ (val >> 16));
}
using namespace std;
int main() {
int a[20];
for ( int i = 0; i < 20; i++ )
cout << Hash( a + i ) << endl;
}
Output:
64641
64645
64889
64893
64881
64885
64873
64877
64865
64869
64857
64861
64849
64853
64841
64845
64833
64837
64825
64829
The reinterpret_cast allows the pointer to be treated as an integral type. The result is then bit-shifted and XORed with itself to produce a unique index (unique to a high degree of probability). The index is then truncated by a standard C-style cast to the return type of the function.