This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21 Core Issues List revision 115e. See http://www.open-std.org/jtc1/sc22/wg21/ for the official list.

2024-11-11

467. Jump past initialization of local static variable

Section: 8.8  [stmt.dcl]     Status: NAD     Submitter: Kerch Holt     Date: 31 Mar 2004

When jumping past initialization of a local static variable the value of the static becomes indeterminate. Seems like this behavior should be illegal just as it is for local variables with automatic linkage.

Here is an example:

struct X {
    X(int i) : x(i) {}
    int x;
};
int f(int c) {
    if (c)
        goto ly;    // error here for jumping past next stmt.
    static X a = 1;
ly:
    return a.x;  // either 1 or 0 depending on implementation.
}

8.8 [stmt.dcl] P3 should be changed to:

A program that jumps from a point where a local variable with automatic or static storage duration is not in scope to a point where it is in scope is ill-formed unless the variable has POD type (3.9) and is declared without an initializer (8.5).
This would imply "static X a = 1;" should be flagged as an error. Note that this behavior a may be a "quality of implementation issue" which may be covered in 6.7 P4. Paragraph 4 seems to make the choice of static/dynamic initialization indeterminate. Making this an error and thus determinate seems the correct thing to do since that is what is already required of automatic variables.

Steve Adamczyk: Some version of this may be appropriate, but it's common to have code that is executed only the first time it is reached, and to have an initialization of a static variable inside such a piece of code. In such a case, on executions after the first there is indeed a jump over the declaration, but the static variable is correctly initialized -- it was initialized the first time the routine was called.

  void f() {
    static bool first_time = true;
    if (!first_time) goto after_init;
    static int i = g();
    first_time = false;
  after_init:
    ...
  }

Rationale (October, 2004):

The CWG sees no reason to change this specification. Local static variables are different from automatic variables: automatic variables, if not explicitly initialized, can have indeterminate (“garbage”) values, including trap representations, while local static variables are subject to zero initialization and thus cannot have garbage values.

The latitude granted to implementations regarding performing dynamic initialization of local static objects as if it were static initialization is exactly parallel to namespace scope objects (6.9.3.2 [basic.start.static]), as are the restrictions on programmer assumptions.