Hello everyone,
in c99 I can make a struct with a flexible array member at the end. Is it possible to create such a variable at compile time?
e.g:
struct monitoredArray { unsigned int const arrSize; unsigned int nUsed; uint8_t array[]; }; static struct monitoredArray myArray = {10, 0, [10] /* this won't work... */};
I'd like to use this for a generic kind of initialization (in respect to the array size) so I can use this in different modules without big modification or use of malloc and an init-function. I just want to know how to write that [10] in the example above.
Thanks Alexander
Use a pointer and have the array either NULL-terminated, or store the number of elements.
#define NELEM(a) (sizeof(a)/sizeof(a[0])) elemt_t elements_a[] = { {...}, {...}, ... }; monitor_t my_monitored_info = { "a","TCP",10,127,NELEM(elements_a),elements_a }; monitor_t my_other_monitored_info = { "b","UDP",19,32,NELEM(elements_b),elements_b }; ... process_elements(&my_monitored_info); process_elements(&my_other_monitored_info);
All statically allocated during build time.
Is it possible to create such a variable at compile time?
Yes. But you can't initialize the flexible-array element, because it's not really considered part of the struct.
It would be rather pointless anyway. What good is that flexibility if you're not going to use it, but instead fix the size of that array at compile time?
I don't want to create to initialize the array elements. The purpose is to write a managed container for data like a fifo. The user should be able to create a variable of that type and use it with provided functions:
fifoRet_t fifo_push(fifo_t * pFifo, int elem) fifoRet_t fifo_pop(fifo_t * pFifo, int * elem)
I want it to be as convenient as possible, so I don't want to use a init function but provide a generic size for the buffer.
My current solution is the following:
typedef struct fifo_s { uint32_t nextRead; uint32_t nWritten; uint32_t const sizePerElement; uint32_t const nElements; int * const container; }fifo_t; #define FIFO_DECLARE(name,numElements) \ int name##_container[ (numElements) ]; \ fifo_t name = {0,0,(numElements) , (& name##_container[0])}
What I don't like about this is that it is not possible to create both the container and the fifo_t element static with
static FIFO_DECLARE(foo,128);
Then I was reading about the new language features in c99 and read about the flexible array elements. Now I think I can create my buffer with those.