Is gcc or clang correct about this behavior?

Question

I have a little toy program:

static int value = 0;  int function(int &value=value) {     return value; }  int main() {     function(); } 

Compiling with g++ 7.2:

g++ -std=c++11 -Wall -Wextra test.cc -o test

No problem.

Compiling with clang++-3.9:

clang++-3.9 -std=c++11 -Wall -Wextra test.cc -o test

test.cc:3:25: error: default argument references parameter 'value' int function(int &value=value) {                         ^~~~~ test.cc:8:5: error: no matching function for call to 'function'     function();     ^~~~~~~~ test.cc:3:5: note: candidate function not viable: requires single argument 'value', but no arguments were provided int function(int &value=value) {     ^ 2 errors generated. 

Kaboom. Who's right?

Answer 1

I think clang is correct. From basic.scope.pdecl:

The point of declaration for a name is immediately after its complete declarator (Clause [dcl.decl]) and before its initializer (if any), except as noted below. [ Example:

int x = 12;{ int x = x; } 

Here the second x is initialized with its own (indeterminate) value. — end example ]

Also, from dcl.fct.default:

Default arguments are evaluated each time the function is called. The order of evaluation of function arguments is unspecified. Consequently, parameters of a function shall not be used in a default argument, even if they are not evaluated. Parameters of a function declared before a default argument are in scope and can hide namespace and class member names