c - MDK-ARM C错误: expression must have a constant value

Question

我正在使用RealView(基于ARMCC)编译器的MDK-ARM环境中编写基于状态机的嵌入式C代码。

IDE 生成错误:

error: #28: expression must have a constant value.

部分代码如下:

struct wspace
{
    struct netimer period;
    struct nequeue deferred;
    struct nevent *deferred_queue_storage[EPA_EEPROM_QUEUE_SIZE];
    struct nepa *producer;
    struct event_i2c_transfer transfer;
    uint32_t i2c_retry;
    uint8_t i2c_buffer[3];
    uint32_t address;
    uint8_t *raw_buffer;
    uint32_t size;
    uint32_t idx;
    uint32_t max_size;
    uint32_t dev_id;
};

static naction state_init_eeprom(struct nsm * sm, const struct nevent * event) {
    struct wspace * ws = nsm_wspace(sm);

    switch (event->id) {
        case NSM_INIT : {
            struct nequeue_define deferred_queue =
            **NEQUEUE_DEF_INIT(ws->deferred_queue_storage, sizeof(ws->deferred_queue_storage));** // this is the line pointed by compiler

            netimer_init(&ws->period);
            nequeue_init(&ws->deferred, &deferred_queue);
            ws->transfer.super          = g_default_event;
            ws->transfer.super.producer = nepa_get_current();
            ws->transfer.dev_id         = EEPROM_I2C_ID;
            ws->transfer.timeout_ms     = EEPROM_I2C_TIMEOUT_MS;
            ws->max_size                = 8 * 1024;
            ws->dev_id                  = EEPROM_I2C_ID;

            return (naction_transit_to(sm, state_idle));
        }
        default : {
            return (naction_ignored());
        }
    }
}

重要定义:

#define NEQUEUE_SIZEOF(elements)                                                
    (sizeof(struct nevent * [elements]))

#define NEQUEUE_DEF_INIT(storage, size)                                         
    {storage, size}     

struct nequeue_define
{
    struct nevent ** storage;/**<@brief Allocated memory storage   */
    size_t size;   /**<@brief Size of queue in bytes     */
};


struct nequeue
{
    struct nqueue               queue;
    #if (CONFIG_REGISTRY == 1)
    ncore_reg                   min;
    #endif
    #if (CONFIG_API_VALIDATION == 1)
    unsigned int                signature;
    #endif
};

我在这个主题上发现的所有内容都与以下事实有关:常量变量不能作为初始值设定项分配给数组的元素或结构的成员，即使它之前已经初始化过。

有人知道如何解决这个问题吗？

Answer 1

您不能在常量表达式中使用变量的内容，并且您的结构初始化器是常量表达式。

虽然 sizeof(ws->deferred_queue_storage) 没问题，因为它的值可以在编译时确定； ws->deferred_queue_storage 无效，因为该变量的内容可以是任何内容。

解决方案是在分配后使用赋值:

struct nequeue_define deferred_queue;
deferred_queue.storage = ws->deferred_queue_storage;
deferred_queue.size = sizeof(ws->deferred_queue_storage);