C++ syntax basics: what is the only technical difference between a struct and a class in C++ (ignoring stylistic conventions)?

Introduction / Context:
In modern C++, structs and classes are nearly identical constructs. The notable distinction is their default access level, which affects encapsulation when you omit explicit access specifiers.

Given Data / Assumptions:

• Both struct and class can contain data members, member functions, constructors, destructors, and even inheritance.
• Access specifiers available: public, protected, private.
• We focus on defaults when none are specified.

Concept / Approach:
By default, members of a struct are public; members of a class are private. Likewise for base-class inheritance: struct defaults to public inheritance, class to private inheritance. Otherwise, capabilities are the same. You can override defaults with explicit access specifiers.

Step-by-Step Solution:
1) struct S { int x; }; → x is public by default.2) class C { int x; }; → x is private by default.3) struct D : Base {}; → public inheritance by default; class E : Base {}; → private by default.4) Functionality (constructors, operators, templates) is shared; only defaults differ.

Verification / Alternative check:
Compile code accessing S::x directly vs C::x; you will see that access to C::x fails unless made public.

Why Other Options Are Wrong:
Protected-by-default: incorrect for both forms.“Structs cannot have member functions”: false—structs are classes under a different keyword.

Common Pitfalls:
Assuming “struct is C-style POD only”—not true in C++; use struct for passive aggregates by convention, but it has full class features.

Final Answer:
Member function and data are by default public in structures but private in classes.