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1. The incomplete array type must be the last element within the structure.
2. There cannot be an array of structures that contain flexible array members.
3. Structures that contain a flexible array member cannot be used as a member in the middle of another structure.
4. The sizeof operator cannot be applied to a flexible array.

Automated Detection

The tool Compass / ROSE could try flagging violations of this rule simply by searching for structs where the last element is an array, with a small index (0 or 1). Alternately, it could flag violations by searching for arguments to malloc() of the form sizeof( struct) * sizeof( arraytype ) - 1.

Risk Assessment

Failing to use the correct syntax can result in undefined behavior, although the incorrect syntax will work on most implementations.

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