Error 28: Expression must have a constant value

问题

I have a section of c++ code in keil uvision5 that is getting error 28: expression must have a constant value. I am trying to figure out how to fix it.

this is the line (inside of a function) that it is happening on:

osPoolDef_t pool_def = { queue_def->queue_sz,  queue_def->item_sz};

it does not like the variables queue_sz or item_sz.

here is the definition of osPoolDef_t:

typedef const struct os_pool_def  {
  uint32_t                 pool_sz;    /*  number of items (elements) in the pool */
  uint32_t                 item_sz;    /*  size of an item */
  void                     *pool;      /*  pointer to memory for pool */
} osPoolDef_t;

and queue_def is a pointer to osMailQDef_t shown below:

typedef const struct os_mailQ_def  {
  uint32_t                queue_sz;    /*  number of elements in the queue */
  uint32_t                 item_sz;    /*  size of an item */
  struct os_mailQ_cb **cb;
} osMailQDef_t;

hopefully that is enough information.

It seems that the problem is that I am not using c99 anymore, but the code worked fine for that file when I used c99. Is there a way to force the compilation of just that file to be done with c99?

回答1:

You can force the armcc compiler to use C99 with the --c99 option.

来源：https://stackoverflow.com/questions/24528084/error-28-expression-must-have-a-constant-value