Statically initializing array inside struct upon struct initialization

Question

I am trying to build a ring buffer by using statically allocated array (requirement, already built dinamical, later decided to go statical). However, I would like to have a generic ring buffer structure that would enable instantiating different sizes of arrays inside of it. I have this structure:

typedef struct measurementsRingBuffer
{   
    int maxSize;
    int currentSize;
    double measurementsArray[MEAS_ARRAY_CAPACITY];
} measurementsRingBuffer;

I instantiate the structure by:

measurementsRingBuffer buffer = { .maxSize = MEAS_ARRAY_CAPACITY, .currentSize = 0 };

Is there any way I could define array size upon struct instantiation, instead of defining it in structure itself? I does not sound possible, but I will give it a shot.

I'm not sure but if you use a pointer instead of an array, and if the array is the last member of your structure, then I guess you can decide of its size when you allocate the memory. Anyway instead of having sizeof(measurementsRingBuffer) you will have the cumulated size of all the members plus n*sizeof(double) with n the size of your array — Tim
– Tim, Commented Jul 4, 2016 at 9:50
It is real-time system with strict memory consumption requirements. It needs to know how much memory will be needed. — omegasbk
– omegasbk, Commented Jul 4, 2016 at 9:50
If the array is defined before the structure is defined, you could simply use sizeof(the_array) as array size. — Lundin
– Lundin, Commented Jul 4, 2016 at 12:47

2501 · Accepted Answer · 2016-07-04 09:53:22Z

6

You can use a pointer to an array:

typedef struct measurementsRingBuffer
{   
    int maxSize;
    int currentSize;
    double* measurementsArray ;
} measurementsRingBuffer;

double small_array[10];
measurementsRingBuffer small = { .maxSize = 10 , .measurementsArray = small_array } ;

or even a compound literal:

measurementsRingBuffer small = { .maxSize = 10 , .measurementsArray = ( double[10] ){ 0 } } ;

Note that the if compound literal is defined outside of a body of a function, it has static storage duration.

edited Jul 4, 2016 at 9:53

answered Jul 4, 2016 at 9:50

2501

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1 Comment

omegasbk Over a year ago

Nice! This sounds correct, gonna try it. Thanks a lot!

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