<cxxabi.h>The <cxxabi.h> header is part of the C++ Application Binary Interface (ABI) and is typically used for low-level operations related to the C++ runtime, particularly for name demangling and exception handling. This header is not part of the C++ Standard Library but is provided by many C++ implementations, especially those based on the GNU Compiler Collection (GCC).
#include <iostream>
#include <cxxabi.h>
#include <memory>
#include <typeinfo>
template <typename T>
std::string demangle_type_name(const char* mangled_name) {
int status;
std::unique_ptr<char, void(*)(void*)> result(
abi::__cxa_demangle(mangled_name, nullptr, nullptr, &status),
std::free
);
return (status == 0) ? result.get() : mangled_name;
}
class MyClass {};
int main() {
std::cout << "Mangled name: " << typeid(MyClass).name() << std::endl;
std::cout << "Demangled name: " << demangle_type_name<MyClass>(typeid(MyClass).name()) << std::endl;
return 0;
}
abi::__cxa_demangle to convert a mangled name to a human-readable form.typeid().name() returns the mangled name of a type.unique_ptr with a custom deleter to ensure proper memory management.#include <iostream>
#include <cxxabi.h>
#include <memory>
#include <string>
std::string demangle(const char* mangled_name) {
int status;
std::unique_ptr<char, void(*)(void*)> result(
abi::__cxa_demangle(mangled_name, nullptr, nullptr, &status),
std::free
);
return (status == 0) ? result.get() : mangled_name;
}
template <typename T>
void print_function_name(T func) {
std::cout << "Function name: " << demangle(typeid(func).name()) << std::endl;
}
void simple_function() {}
class MyClass {
public:
void member_function() {}
};
int main() {
print_function_name(simple_function);
print_function_name(&MyClass::member_function);
return 0;
}
print_function_name is a template function that can work with different function types.typeid to get the mangled name of the function, then demangle it.#include <iostream>
#include <exception>
void terminate_handler() {
std::cout << "Custom terminate handler called" << std::endl;
std::abort();
}
void throw_unexpected() noexcept(false) {
throw std::runtime_error("Unexpected exception");
}
int main() {
std::set_terminate(terminate_handler);
try {
throw_unexpected();
} catch (const std::runtime_error& e) {
std::cout << "Caught runtime_error exception: " << e.what() << std::endl;
} catch (...) {
std::cout << "Caught unknown exception" << std::endl;
}
return 0;
}
This example demonstrates the use of custom terminate handlers and exception handling in C++.
terminate_handler() is defined as a custom terminate handler. It prints a message and calls std::abort() to terminate the program.
std::set_terminate(terminate_handler) is used to set our custom function as the terminate handler. This handler is called when the program terminates unexpectedly, such as when an exception is thrown and not caught.
throw_unexpected() is a function declared with noexcept(false), which means it's allowed to throw exceptions. It throws a std::runtime_error.
In the main() function, we use a try-catch block to handle exceptions:
try block calls throw_unexpected().catch block catches std::runtime_error specifically.The second catch (...) block is a catch-all for any other type of exception.
When throw_unexpected() is called, it throws a std::runtime_error which is caught by the first catch block. The program prints the error message and continues execution.
If throw_unexpected() were to throw a different type of exception, it would be caught by the catch-all block.
The custom terminate handler is not called in this case because all exceptions are properly caught. It would only be invoked if an exception escaped the main function or if std::terminate() was called explicitly.
This code illustrates proper exception handling practices and how to set up custom terminate handlers, which can be useful for logging or performing cleanup operations in case of unexpected program termination.
#include <iostream>
#include <cxxabi.h>
#include <exception>
#include <stdexcept>
#include <typeinfo>
void print_exception_info(const std::exception& e) {
const std::type_info& ti = typeid(e);
int status;
char* demangled_name = abi::__cxa_demangle(ti.name(), nullptr, nullptr, &status);
std::cout << "Exception type: " << (status == 0 ? demangled_name : ti.name()) << std::endl;
std::cout << "Exception message: " << e.what() << std::endl;
if (demangled_name) {
free(demangled_name);
}
}
int main() {
try {
throw std::runtime_error("This is a runtime error");
} catch (const std::exception& e) {
print_exception_info(e);
}
try {
throw std::logic_error("This is a logic error");
} catch (const std::exception& e) {
print_exception_info(e);
}
return 0;
}
typeid to get the type information of the caught exception.abi::__cxa_demangle is used to get the readable name of the exception type.#include <iostream>
#include <cxxabi.h>
#include <new>
void* operator new(std::size_t size) {
std::cout << "Custom global new called, size: " << size << std::endl;
return std::malloc(size);
}
void operator delete(void* ptr) noexcept {
std::cout << "Custom global delete called" << std::endl;
std::free(ptr);
}
class MyClass {
public:
MyClass() { std::cout << "MyClass constructor" << std::endl; }
~MyClass() { std::cout << "MyClass destructor" << std::endl; }
};
int main() {
try {
MyClass* obj = new MyClass();
throw std::runtime_error("Test exception");
delete obj; // This won't be called
} catch (...) {
std::cout << "Exception caught" << std::endl;
}
// Force cleanup of any undeleted objects
abi::__cxa_finalize(nullptr);
return 0;
}
new and delete operators for demonstration.abi::__cxa_finalize is called to ensure proper cleanup of static objects and those not properly deleted due to exceptions.Portability: <cxxabi.h> is not part of the C++ Standard and may not be available or may behave differently on non-GCC compilers.
Memory Management: When using functions like __cxa_demangle, be careful to properly free the allocated memory to avoid leaks.
Performance Impact: Demangling operations can be relatively expensive and should be used judiciously, especially in performance-critical code.
Compiler Dependence: The exact behavior and availability of ABI functions can vary between compiler versions and implementations.
Debug vs Release: Some ABI functionalities might behave differently or be unavailable in release builds compared to debug builds.
The <cxxabi.h> header provides low-level utilities for working with the C++ ABI:
While powerful, <cxxabi.h> should be used with caution due to its non-standard nature. It's particularly useful in scenarios where you need to interact with the low-level details of C++ runtime behavior, such as in debuggers, profilers, or when implementing custom exception handling or memory management schemes.
The functionalities provided by <cxxabi.h> are often essential for tools that need to introspect or manipulate C++ programs at a low level. However, for most application-level C++ programming, the standard facilities provided by the C++ Standard Library are sufficient and preferred for their portability and standardized behavior.