Defect Report #339

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Submitter: Joseph Myers (UK)
Submission Date: 2007-03-24
Source: Joseph Myers <>
Reference Document: ISO/IEC WG14 N1120
Version: 1.4
Date: 2008-07-21
Subject: Variably modified compound literals


Consider the code:

    extern int a;
    void *p = &(int (*)[a]){ 0 };

Does such a variably modified compound literal at file scope violate any constraint? says:

[#2] Only an ordinary identifier (as defined in 6.2.3) with both block scope or function prototype scope and no linkage shall have a variably modified type. If an identifier is declared to be an object with static storage duration, it shall not have a variable length array type.

However, this only seems to constrain declarations of identifiers, not any other expression with variably modified type (such as a compound literal, inside or outside a function). If however the above code is valid, when is a evaluated for the purposes of the requirement in that "each time it is evaluated it shall have a value greater than zero"? Must a have positive value throughout execution of the program, or is it only the initial value of a which must be positive? (I think the initializer is a constant expression, being the address of an object of static storage duration.)

The variably modified compound literal is an object, and I think it should be treated like other objects outside functions and required not to have variably modified type (even if inside sizeof, just like the initializers of compound literals outside functions must be constant even if inside sizeof).

Suggested Technical Corrigendum paragraph 3, after "shall consist of constant expressions" add "and the type name shall not specify a variably modified type".

Committee Discussion

Paragraph in question (paragraph 3 of has been changed by DR 328.

The suggested Technical Corrigendum looks appropriate, however, it could be redundant.

Committee Response

This defect report is answered by DR 328.

Constraints and Semantics are the same as 6.7.8 Initialization

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