A declaration disguised as a variable

#include <iostream>

struct Widget {
    Widget() {}
    void greet() { std::cout << "hi\n"; }
};

int main() {
    Widget w();
    w.greet();
}

Widget w(); does not declare a variable — it declares a function named w returning Widget. So w.greet() fails. GCC says so directly, and even suggests the fix:

warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
error: request for member 'greet' in 'w', which is of non-class type 'Widget()'

This program does not compile, so there is no runtime output to quote.

Fix: Widget w; or Widget w{};.

Lesson: when a declaration can be read as a function, the compiler reads it as a function.

Facts verified 2026-11-04. The code on this page was compiled and run on the box with GCC 16.2.0 at -std=c++23 -Wall -Wextra; the outputs quoted are the observed outputs. MSVC was not tested.

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