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66fb5a29bb
Apply the pre-commit hook whitespace fixes to all files in the repo. (Line endings, blank lines at end of file, trailing whitespace)
101 lines
3.0 KiB
C++
101 lines
3.0 KiB
C++
/* C++ run-time type info (RTTI) example
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This example code is in the Public Domain (or CC0 licensed, at your option.)
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Unless required by applicable law or agreed to in writing, this
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software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
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CONDITIONS OF ANY KIND, either express or implied.
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*/
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#include <iostream>
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#include <memory>
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#include <vector>
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#include <algorithm>
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#include <cxxabi.h>
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using std::cout;
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using std::endl;
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using std::string;
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using std::shared_ptr;
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using std::make_shared;
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class Base;
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class DerivedA;
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class DerivedB;
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static string demangle(const char* name);
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class Base
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{
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public:
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virtual ~Base() {} ;
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virtual string name() = 0;
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static shared_ptr<Base> make_random_derived();
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};
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class DerivedA : public Base
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{
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public:
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string name() override { return "DerivedA"; }
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};
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class DerivedB : public Base
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{
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public:
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string name() override { return "DerivedB"; }
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};
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/* Creates either DerivedA or DerivedB, depending on a random number */
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shared_ptr<Base> Base::make_random_derived()
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{
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if (std::rand() % 2 == 0) {
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return make_shared<DerivedA>();
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} else {
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return make_shared<DerivedB>();
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}
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}
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/* Inside a .cpp file, app_main function must be declared with C linkage */
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extern "C" void app_main()
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{
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/* Demonstrate typeid().name() */
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cout << "Type names of a few objects:" << endl << '\t';
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cout << "Type name of std::cout is: " << demangle(typeid(std::cout).name()) << endl << '\t';
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cout << "Type name of std::cin is: " << demangle(typeid(std::cin).name()) << endl << '\t';
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cout << "Type of app_main is: " << demangle(typeid(app_main).name()) << endl << '\t';
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auto sum = [](int x, int y) -> int { return x + y; };
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cout << "Type name of a lambda function is: " << demangle(typeid(sum).name()) << endl << endl;
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/* Demonstrate dynamic_cast */
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std::vector<shared_ptr<Base>> objects(5);
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cout << "Generating " << objects.size() << " random objects and printing their types:" << endl;
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std::generate(objects.begin(), objects.end(), Base::make_random_derived);
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for (auto &obj: objects) {
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cout << "obj->name() is: " << obj->name() << endl << '\t';
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cout << "typeid(*obj).name() is: " << demangle(typeid(*obj).name()) << endl << '\t';
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const DerivedA* cast_to_derived_a = dynamic_cast<DerivedA*>(obj.get());
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const DerivedB* cast_to_derived_b = dynamic_cast<DerivedB*>(obj.get());
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cout << "dynamic_cast<DerivedA*>(obj)=" << static_cast<const void*>(cast_to_derived_a) << endl << '\t';
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cout << "dynamic_cast<DerivedB*>(obj)=" << static_cast<const void*>(cast_to_derived_b) << endl << endl;
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}
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cout << "Example finished." << endl;
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}
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/* Helper function which converts typeid().name() to a human-readable type name */
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static std::string demangle(const char* name)
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{
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int status = 0;
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char* result = abi::__cxa_demangle(name, NULL, NULL, &status);
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string str_result;
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if (status == 0) {
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str_result = result;
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} else {
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str_result = name;
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}
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free(result);
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return str_result;
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}
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