1 /* C++ run-time type info (RTTI) example
2
3 This example code is in the Public Domain (or CC0 licensed, at your option.)
4
5 Unless required by applicable law or agreed to in writing, this
6 software is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
7 CONDITIONS OF ANY KIND, either express or implied.
8 */
9
10 #include <iostream>
11 #include <memory>
12 #include <vector>
13 #include <algorithm>
14 #include <cxxabi.h>
15
16 using std::cout;
17 using std::endl;
18 using std::string;
19 using std::shared_ptr;
20 using std::make_shared;
21
22 class Base;
23 class DerivedA;
24 class DerivedB;
25
26 static string demangle(const char* name);
27
28 class Base
29 {
30 public:
~Base()31 virtual ~Base() {} ;
32 virtual string name() = 0;
33 static shared_ptr<Base> make_random_derived();
34 };
35
36 class DerivedA : public Base
37 {
38 public:
name()39 string name() override { return "DerivedA"; }
40 };
41
42 class DerivedB : public Base
43 {
44 public:
name()45 string name() override { return "DerivedB"; }
46 };
47
48 /* Creates either DerivedA or DerivedB, depending on a random number */
make_random_derived()49 shared_ptr<Base> Base::make_random_derived()
50 {
51 if (std::rand() % 2 == 0) {
52 return make_shared<DerivedA>();
53 } else {
54 return make_shared<DerivedB>();
55 }
56 }
57
58 /* Inside a .cpp file, app_main function must be declared with C linkage */
app_main()59 extern "C" void app_main()
60 {
61 /* Demonstrate typeid().name() */
62 cout << "Type names of a few objects:" << endl << '\t';
63 cout << "Type name of std::cout is: " << demangle(typeid(std::cout).name()) << endl << '\t';
64 cout << "Type name of std::cin is: " << demangle(typeid(std::cin).name()) << endl << '\t';
65 cout << "Type of app_main is: " << demangle(typeid(app_main).name()) << endl << '\t';
66 auto sum = [](int x, int y) -> int { return x + y; };
67 cout << "Type name of a lambda function is: " << demangle(typeid(sum).name()) << endl << endl;
68
69 /* Demonstrate dynamic_cast */
70 std::vector<shared_ptr<Base>> objects(5);
71 cout << "Generating " << objects.size() << " random objects and printing their types:" << endl;
72 std::generate(objects.begin(), objects.end(), Base::make_random_derived);
73 for (auto &obj: objects) {
74 cout << "obj->name() is: " << obj->name() << endl << '\t';
75 cout << "typeid(*obj).name() is: " << demangle(typeid(*obj).name()) << endl << '\t';
76
77 const DerivedA* cast_to_derived_a = dynamic_cast<DerivedA*>(obj.get());
78 const DerivedB* cast_to_derived_b = dynamic_cast<DerivedB*>(obj.get());
79
80 cout << "dynamic_cast<DerivedA*>(obj)=" << static_cast<const void*>(cast_to_derived_a) << endl << '\t';
81 cout << "dynamic_cast<DerivedB*>(obj)=" << static_cast<const void*>(cast_to_derived_b) << endl << endl;
82 }
83
84 cout << "Example finished." << endl;
85 }
86
87 /* Helper function which converts typeid().name() to a human-readable type name */
demangle(const char * name)88 static std::string demangle(const char* name)
89 {
90 int status = 0;
91 char* result = abi::__cxa_demangle(name, NULL, NULL, &status);
92 string str_result;
93 if (status == 0) {
94 str_result = result;
95 } else {
96 str_result = name;
97 }
98 free(result);
99 return str_result;
100 }
101
