Potential pointer corruption

When porting a program from ILP32 to LP64, be aware of the following potential problems:

• An invalid address might be the result of either of the following actions:
  • Assigning an integer (4 bytes) or a 4-byte hexadecimal constant to a pointer type variable (8 bytes)
  • Casting a pointer to an integer type
  Note: An invalid address causes errors when the pointer is dereferenced.
• If you compare an integer to a pointer, you might get unexpected results.
• Data truncation might result if you convert pointers to signed or unsigned integers with the expectation that the pointer value will be preserved.
• If return values of functions that return pointers are assigned to an integer type, those return values will be truncated.
• If code assumes that pointers and integers are the same size (in an arithmetic context), there will be problems. Pointer arithmetic is often a source of problems when migrating code. The ISO C and C++ standards dictate that incrementing a pointer adds the size of the data type to which it points to the pointer value. For example, if the variable p is a pointer to long, the operation (p+1) increments the value of p by 4 bytes (in 32-bit mode) or by 8 bytes (in 64-bit mode). Therefore, casts between long* and int* are problematic because of the size differences between pointer objects (32 bits versus 64 bits).