C++03 Changes and Corrections

Value Initialization

C++03 clarified three initialization semantics:

int a;          // Default initialization (for built-in types: indeterminate value)
int b = int();  // Value initialization (for built-in types: zero initialization) → b = 0
int c();        // Note: this is a function declaration! (most vexing parse)

For class types:

struct Widget {
    int x;
    double y;
};

Widget w1;         // Default initialization: calls the default constructor
Widget w2 = Widget();  // Value initialization: zero-initialized first, then calls the default constructor

Two-Phase Name Lookup for Templates

C++03 refined the two-phase name lookup rules in templates:

1. Phase 1 (at template definition): Lookup of non-dependent names
2. Phase 2 (at template instantiation): Lookup of dependent names

template<typename T>
void foo(T t) {
    bar(t);        // Dependent name — looked up in Phase 2
    baz();         // Non-dependent name — looked up in Phase 1
}

This ensures that template code can detect a subset of errors at definition time, rather than deferring all errors to instantiation.

Other Corrections

• Corrections to std::allocator member functions
• Refinement of exception specification behavior
• Fixes for several Defect Reports in library implementations