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Flexible array members are defined in Section 6.7.2.1, paragraph 16 of the C99 standard as follows,:

As a special case, the last element of a structure with more than one named member may have an incomplete array type; this is called a flexible array member. In most situations, the flexible array member is ignored. In particular, the size of the structure is as if the flexible array member were omitted, except that it may have more trailing padding than the omission would imply. However, when a . (or ->) operator has a left operand that is (a pointer to) a structure with a flexible array member and the right operand names that member, it behaves as if that member were replaced with the longest array (with the same element type) that would not make the structure larger than the object being accessed; the offset of the array shall remain that of the flexible array member, even if this would differ from that of the replacement array. If this array would have no elements, it behaves as if it had one element but the behavior is undefined if any attempt is made to access that element or to generate a pointer one past it.

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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.

Guideline MEM33-C. Allocate and copy structures containing flexible array members dynamically describes how to allocate and copy structures containing flexible array members.

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The problem with using this approach is that the behavior is undefined when accessing other than the first element of data. (see See Section 6.5.6, Paragraph 8 of the C99 standard.) . Consequently, the compiler can generate code that does not return the expected value when accessing the second element of data.

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\[[ISO/IEC 9899:1999|AA. Bibliography#ISO/IEC 9899-1999]\] Section 6.7.2.1, "Structure and union specifiers"
\[[McCluskey 012001|AA. Bibliography#McCluskey 01]\] ;login:, July 2001, Volume 26, Number 4

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