Robust Casting Solution for C++ Data Integrity

Safeguarding Data Integrity: A Robust Casting Solution

When working with C++, casting between data types can be a minefield, fraught with potential pitfalls. Losing values, incorrect addresses, and undefined behavior are just a few of the risks involved. To mitigate these risks, we can create a generic checked cast function that verifies casts in debug mode and optimizes performance in release mode.

The Challenges of Casting

Casting between data types can go awry in several ways:

• Losing values when casting to an integer type of lower bit length
• Losing values when casting a negative value to an unsigned integer
• Incorrect addresses when casting from a pointer to an integer type other than uintptr_t
• Precision loss when casting from double to float
• Undefined behavior when casting between pointers without a common base class

Introducing Safe Cast

Our safe_cast() function is designed to handle these challenges by performing different checks based on the types being cast. If the cast is not verified, it won’t compile.

Verified Cast Scenarios

Safe_cast() handles the following scenarios:

• Same type: Returns the input value
• Pointer to pointer: Performs a dynamic cast in debug mode to verify castability
• Double to floating point: Accepts precision loss, except when casting from a double to a float that’s too large to handle
• Arithmetic to arithmetic: Verifies no precision is lost by casting back to the original type
• Pointer to non-pointer: Verifies the destination type is uintptrt or intptrt, the only integer types guaranteed to hold an address

Implementing Safe Cast

To implement safe_cast(), we start by fetching information about the cast operation using constexpr booleans. These booleans are used in if constexpr expressions to determine the cast’s validity.

cpp
template <typename T> constexpr auto make_false() { return false; }
template <typename Dst, typename Src>
auto safe_cast(const Src& v) -> Dst{
using namespace std;
constexpr auto is_same_type = is_same_v<Src, Dst>;
constexpr auto is_pointer_to_pointer =
is_pointer_v<Src> && is_pointer_v<Dst>;
constexpr auto is_float_to_float =
is_floating_point_v<Src> && is_floating_point_v<Dst>;
constexpr auto is_number_to_number =
is_arithmetic_v<Src> && is_arithmetic_v<Dst>;
constexpr auto is_intptr_to_ptr =
(is_same_v<uintptr_t,Src> || is_same_v<intptr_t,Src>)
&& is_pointer_v<Dst>;
constexpr auto is_ptr_to_intptr =
is_pointer_v<Src> &&
(is_same_v<uintptr_t,Dst> || is_same_v<intptr_t,Dst>);


Compile-Time Verification

We use static_assert() to verify the cast at compile time. If the condition is not satisfied, the code won’t compile.

cpp
if constexpr(is_same_type) {
return v;
}
else if constexpr(is_intptr_to_ptr || is_ptr_to_intptr){
return reinterpret_cast<Dst>(v);
}
else if constexpr(is_pointer_to_pointer) {
//...
}


By using safe_cast(), we can ensure the integrity of our data and prevent common casting errors.