RTTI in Cross-Platform Development
Are there any best practices for using RTTI in cross-platform development to ensure consistent behavior?
Using RTTI in cross-platform development requires careful consideration to ensure consistent behavior across different platforms. Here are some best practices to follow:
Compiler Support and Flags
Ensure that RTTI is enabled on all target platforms. Some compilers disable RTTI by default for performance reasons.
// Check if RTTI is enabled
#if defined(__GXX_RTTI) || defined(_CPPRTTI)
std::cout << "RTTI is enabled\n";
#else
#error "RTTI is required for this code"
#endifConsistent Naming
The output of typeid().name() is implementation-defined and may vary across platforms. Use a consistent naming scheme or implement a custom type name function.
#include <string>
#include <typeinfo>
template <typename T>
std::string getTypeName() {
#ifdef _MSC_VER
return typeid(T).name(); // Visual Studio
#elif defined(__GNUG__)
int status;
char* demangled = abi::__cxa_demangle(
typeid(T).name(), 0, 0, &status);
std::string result(demangled);
free(demangled);
return result; // GCC/Clang
#else
return typeid(T).name(); // Other compilers
#endif
}Exception Handling
Be aware that typeid can throw std::bad_typeid for null pointers. Handle this consistently across platforms.
#include <iostream>
#include <typeinfo>
void printType(const Monster* monster) {
try {
std::cout << "Type: " << typeid(*monster).name();
} catch (const std::bad_typeid& e) {
std::cerr << "Error: " << e.what();
}
}Dynamic Cast
Use dynamic_cast consistently for type-safe downcasting. Be aware that it throws std::bad_cast for references and returns nullptr for pointers and on failure:
Monster* monster = getMonster();
// Dynamic casting a reference
try {
Dragon& dragon = dynamic_cast<Dragon&>(*monster);
// Dragon-specific code
} catch (const std::bad_cast&) {
std::cerr << "Not a Dragon\n";
}
// Dynamic casting a pointer
Dragon* dragon = dynamic_cast<Dragon*>(monster);
if (dragon) {
// Dragon-specific code
} else {
std::cerr << "Not a Dragon\n";
}Performance Considerations
RTTI operations can have different performance implications on different platforms. Use judiciously and consider alternatives in performance-critical code.
// Compile-time alternative to dynamic_cast
template<typename Base, typename Derived>
Derived* fast_cast(Base* base) {
static_assert(
std::is_base_of<Base, Derived>::value,
"Invalid cast"
);
return static_cast<Derived*>(base);
}Platform-Specific Type Information
Be cautious when relying on platform-specific type information. Stick to standard C++ types and avoid assumptions about type sizes or representations.
// Avoid this:
if (typeid(long) == typeid(long long)) {
// This may vary across platforms
}
// Prefer this:
if (sizeof(long) == sizeof(long long)) {
// This is more reliable
}Testing
Thoroughly test RTTI functionality on all target platforms. Use continuous integration with multi-platform builds to catch inconsistencies early.
void testRTTI() {
Monster* monster = new Dragon();
assert(typeid(*monster) == typeid(Dragon));
assert(dynamic_cast<Dragon*>(monster) != nullptr);
delete monster;
}Documentation
Clearly document any platform-specific RTTI behavior or workarounds in your codebase.
/**
* @brief Get the type name of the object
* @note
* On Windows, this returns the decorated name.
* On Unix, this returns the demangled name.
*/
std::string getObjectTypeName() const {
return typeid(*this).name();
}Alternatives to RTTI
Consider using alternatives to RTTI that may provide more consistent cross-platform behavior:
enum class MonsterType { Base, Dragon, Goblin };
class Monster {
public:
virtual MonsterType getType() const {
return MonsterType::Base;
}
};
class Dragon : public Monster {
public:
MonsterType getType() const override {
return MonsterType::Dragon;
}
};By following these best practices, you can ensure more consistent behavior when using RTTI in cross-platform development.
Remember that while RTTI is a powerful feature, it's not always the best solution for every problem. Always consider the specific requirements of your project and the target platforms when deciding how to use RTTI in your cross-platform C++ code.
Run Time Type Information (RTTI) and typeid()
Learn to identify and react to object types at runtime using RTTI, dynamic casting and the typeid() operator