C++ Code Compilation and Behavior Quiz

General Information

• Game to assess understanding: "Don't do this at work".
• Rules:
  • Presenter shows a code snippet.
  • Audience decides if it compiles and predicts the output.
  • Participants shout answers, with 5 to 10 seconds per question.
  • Assume C++ 20.

Code Snippets and Solutions

Boolean Incrementation

• Snippet: bool b = true; ++b; printf("%d", b);
• Question: Does it compile? What's the output?
• Answer: No, because boolean incrementation was deprecated in C++17.

Char Array with Pi

• Snippet: char arr[3] = "Pi"; printf("%s", arr);
• Question: What's the output?
• Answer: The null terminator maintains the string, so output is Pi.

3D Array Conversion

• Snippet: Assign 3D array to a 2D pointer.
• Question: Does it compile? What's the output?
• Answer: Doesn't compile, requires unsigned char pointer of array type.
• Alternative: If using correct type, it prints true.

Array Indexing Trick

• Snippet: Indexing with integer on array.
• Question: Does it compile?
• Answer: Yes, equivalent to adding addresses and dereferencing.

Variadic Function with Fold Expressions

• Snippet: Variadic function with unfold: func(args...)
• Question: Does it compile?
• Answer: Yes, unfolds to a calculation and results in 6.

Struct with Bit Field Overflow

• Snippet: Bit manipulation within struct with bit field.
• Question: Does it compile? What's the output?
• Answer: Compiles, results in an overflow and prints 2.
• Additional: Could be implementation-defined behavior.

Aggregate Initialization for Structs

• Snippet: Struct initialized out of member order.
• Question: Does it compile? What's the output?
• Answer: Doesn't compile, members must be initialized in order.
• Note: Rust-like syntax works in GCC and Clang, not MSVC.

Templated Lambda with Explicit Type

• Snippet: Templated lambda with explicit int type.
• Question: Does it compile?
• Answer: No, cannot specify explicit type on templated lambda.

Constant Evaluated Function

• Snippet: if consteval function returning different values based on evaluation.
• Question: What’s the output?
• Answer: Varies; consteval generally ensures certain behavior.

Struct Inheritance and Operator Overloading

• Snippet: Complex struct inheritance example.
• Question: Does it compile? What's the output?
• Answer: Compiles; used pattern for std::visit, possibly causing a conversion error.

T1 and T2 Inheritance with Operator Overloading

• Snippet: Struct hierarchy with call operator overload.
• Question: What's the output?
• Answer: bang bang question mark. The special member function call overrides the template deduction guide.