A quiz about C++ quirkiness and subtle syntatic constructs to raise awareness for the things that can go wrong.

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C++ Quiz
Felix Morgner
Computer Science
Hochschule f¨ur Technik Rapperswil
February 24, 2016

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What we will see
Quirky stuff
Undefined Behavior
Unspecified things

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Scoring
+1 per correct answer
+1 per correct reason
-1 per wrong answers

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#include <iostream>
struct S {
int memfun() { return 1; }
int memfun() && { return 2; }
};
int main() {
S o{};
std::cout << o.memfun();
std::cout << S{}.memfun();
}

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#include <iostream>
struct B {
virtual ~B() = default;
float a;
float b;
};
struct D : B {
float c;
};
int main() {
// assume: sizeof(float) = 4
// assume: sizeof(void*) = 8
std::cout << sizeof(B) << ’n’;
std::cout << sizeof(D) << ’n’;
}

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#include <iostream>
struct S { };
int main() {
std::cout << sizeof(S) << ’n’;
}

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#include <iostream>
auto f(unsigned long long & n) {
(***(int * * *)n)++;
}
int main() {
int constexpr n{43};
auto p1 = &n;
auto p2 = &p1;
auto p3 = (unsigned long long) &p2;
f(p3);
std::cout << (**(int * * *)p3 == &n) << ’ ’;
std::cout << *p1 << ’ ’ << n << ’n’;
}

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#include <iostream>
int main() {
char const c{’c’};
char * ptr1;
char const * * ptr2{&ptr1};
*ptr2 = &c;
(*ptr1)++;
std::cout << c << ’n’;
}

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#include <iostream>
int main()
{
https://github.com/fmorgner/cppquiz
std::cout << "cppugzhn";
}

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#include <iostream>
struct S {
S() { std::cout << "c"; }
~S() { std::cout << "d"; }
};
int main() {
int i{};
mark:
S s{};
while(!i++) {
goto mark;
}
}

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#include <iomanip>
#include <iostream>
#include <type_traits>
using namespace std;
int main() {
int i, &j = i;
[=]{
cout << std::is_same<decltype( j ), int &>()
<< std::is_same<decltype((j)), int const &>()
<< std::is_same<int &, int const &>();
}();
}

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#include <iostream>
struct A {
A() = default;
A(A const &) { std::cout << "An"; }
};
struct B {
B() = default;
B(B const &) { std::cout << "Bn"; }
};
auto f(B const &) { }
int main() {
A a{};
B b{};
[=]{
std::cout << sizeof(a) << ’n’;
f(b);
}();
}

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#include <iostream>
struct E {
template<typename ...Types>
E(Types const & ...) {}
};
template<typename ...Types>
auto println(Types const & ...args) {
E{(std::cout << args)..., std::cout << ’n’};
}
int main() {
using namespace std::literals;
println("C", ’+’, "+"s, "RocksMySocks");
}

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#include <iostream>
template<typename ...Types>
auto call(Types const & ...) { }
template<typename ...Types>
auto println(Types const & ...args) {
call((std::cout << args)..., std::cout << ’n’);
}
int main() {
using namespace std::literals;
println("C", ’+’, "+"s, "RocksMySocks");
}

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#include <iostream>
#include <string>
#include <vector>
int main() {
auto a = "cppug";
std::vector<std::string> v{a, a, a};
for(auto const & s : v) {
std::cout << s;
}
std::cout << ’n’ << v.size() << ’n’;
}

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#include <iostream>
#include <string>
#include <vector>
int main() {
auto a = "cppug";
std::vector<std::string> v{{a, a, a}};
for(auto const & s : v) {
std::cout << s;
}
std::cout << ’n’ << v.size() << ’n’;
}

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#include <iostream>
#include <string>
#include <vector>
int main() {
auto a = "cppug";
std::vector<std::string> v{{a, a}};
for(auto const & s : v) {
std::cout << s;
}
std::cout << ’n’ << v.size() << ’n’;
}

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#include <iostream>
void f(long) {
std::cout << 1 << ’n’;
}
void f(float) {
std::cout << 2 << ’n’;
}
int main() {
f(4);
}

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#include <iostream>
void f(int, int, int, int);
void f(int, int, int, int = 1);
void f(int, int, int = 2, int);
void f(int, int = 3, int, int);
void f(int = 4, int, int, int);
void f(int a, int b, int c, int d) {
std::cout << a << b << c << d << ’n’;
}
int main() {
f();
}

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#include <iostream>
template<typename T>
void o(T) {
std::cout << 1;
}
template<typename T>
void f(T a) {
o(a);
}
void o(float) {
std::cout << 2;
}
int main() {
f(1.0f);
}

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#include <iostream>
int main() {
auto x = 41; // Is this the right answer ??/
x = 42;
std::cout << x;
}

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int main() <%<:=??)??<??(&:><%??(]<%??>();%>();}();%>

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int main() <%
<:=??)??<
??(&:><%
??(]<%??>();
%>();
}();
%>

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int main() {
[=]{
[&]{
[]{}();
}();
}();
}

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Thanks
https://www.youtube.com/watch?v=rNNnPrMHsAA - Piotr
Padlewski - C++ WAT
http://cppquiz.org/ - C++ Quiz
http://olvemaudal.com/ - Olve Maudal
ISO14882:2014

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Code and Slides
https://github.com/fmorgner/cpp-quiz
http://www.slideshare.net/fmorgner/cpp-quiz