When is `reinterpret_cast` the Necessary Choice for Type Conversion in C ?

When is reinterpret_cast Necessary?

Understanding the distinction between reinterpret_cast and static_cast can be challenging. Generally, static casts are preferred when the type conversion is statically deducible, while reinterpret casts are used in specific scenarios:

• Converting Integer Types to/from Pointers: reinterpret_cast allows conversions between integer types (e.g., int, long) and pointer types (e.g., int*, char*). This can be useful for interacting with memory directly or for achieving low-level optimizations.
• Converting Pointer Types: reinterpret_cast enables conversions between different pointer types (e.g., int* to long*). However, these conversions are specifically discouraged as they may be non-portable and introduce additional complications.

Case Study: C and C Interoperability

In your specific case, where C objects are accessed from C code through a void* pointer, reinterpret_cast is the appropriate choice. The reason for this is that static_cast guarantees preservation of address when casting to and from void*. Therefore, the following code ensures that a, b, and c all refer to the same address:

int* a = new int();
void* b = static_cast<void*>(a);
int* c = static_cast<int*>(b);

In contrast, reinterpret_cast would require explicit recasting to the original pointer type to retain the original value. While reinterpret_cast could be used here, static_cast is preferred for its guaranteed address preservation.

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