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The problem with this code is that the {{flexArrayStruct}} does not actually reserve space for the integer array data:; Itit can't because the size hasn't been specified. Consequently, while initializing the {{num}} member to zero is allowed, attempting to write even one value into data (that is, {{data\[0\]}}) is likely to overwrite memory outside of the object's bounds.

Compliant

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Solution (Storage Allocation)

This compliant solution dynamically allocates storage for struct flexArrayStruct.

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The problem with this noncompliant code example is that when the structure is copied, the size of the flexible array member is not considered

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and only the first member of the structure, num, is copied.

Compliant Solution (Copying)

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struct flexArrayStruct *flexStructA;
struct flexArrayStruct *flexStructB;
size_t array_size;
size_t i;

/* Initialize array_size */

/* Allocate memory for flexStructA */

/* Allocate memory for flexStructB */

/* Initialize flexStructA */

/* ... */

memcpy(
  flexStructB, 
  flexStructA, 
  (sizeof(struct flexArrayStruct) + sizeof(int) * array_size)
);

This compliant solutions solution ensures that the entire structure, including the flexible array member, is copied correctly.

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Flexible array structs should not be

• declared on the stack: They , they should be on the heap.
• copied via assignment: They , they should be copied using memcpy() or a similar function.
• passed as raw arguments to functions; A , a pointer should be passed to flexArrayStruct intead.

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