Initialization of flexible array member in this way is not allowed as per C standard. C11: 6.7.2.1 Structure and union specifiers (p20-21): 21 EXAMPLE 2 After the declaration: struct s { int n; double d[]; }; the structure struct s has a flexible array member d. […] 22 Following the above declaration: struct s t1 … Read more
Does anyone know what I am doing wrong? Trying to use assignment to copy a struct with a flexible array member. From the standard (6.7.2.1): The assignment *s1 = *s2 only copies the member n [i.e. the part of the struct that isn’t a flexible array]; if any of the array elements are within the … Read more
No, flexible arrays must always be allocated manually. But you may use calloc to initialize the flexible part and a compound literal to initialize the fixed part. I’d wrap that in an allocation inline function like this: typedef struct person { unsigned age; char sex; size_t size; char name[]; } person; inline person* alloc_person(int a, … Read more
The C FAQ answers precisely this question. The quick answer is that this structure will include the double array inside the structure rather than a pointer to an array outside the structure. As a quick example, you could use your structure as in this example: struct s mystruct = malloc(sizeof(struct s) + 5 * sizeof(double)); … Read more
This is C99 feature called flexible arrays, the main feature is to allow the use variable length array like features inside a struct and R.. in this answer to another question on flexible array members provides a list of benefits to using flexible arrays over pointers. The draft C99 standard in section 6.7.2.1 Structure and … Read more
C++ was first standardized in 1998, so it predates the addition of flexible array members to C (which was new in C99). There was a corrigendum to C++ in 2003, but that didn’t add any relevant new features. The next revision of C++ (C++2b) is still under development, and it seems flexible array members still … Read more
It is an accepted “fact” that using goto is poor software engineering practice. That doesn’t make it true. There are times when goto is useful, particularly when handling cleanup and when porting from assembler. Flexible array members strike me as having one main use, off the top of my head, which is mapping legacy data … Read more
Yes this is a C-Hack. To create an array of any length: struct someData* mallocSomeData(int size) { struct someData* result = (struct someData*)malloc(sizeof(struct someData) + size * sizeof(BYTE)); if (result) { result->nData = size; } return result; } Now you have an object of someData with an array of a specified length.
This is a way to have variable sizes of data, without having to call malloc (kmalloc in this case) twice. You would use it like this: struct bts_action *var = kmalloc(sizeof(*var) + extra, GFP_KERNEL); This used to be not standard and was considered a hack (as Aniket said), but it was standardized in C99. The … Read more