c - 函数结束后如何处理函数中声明的变量

Question

我想知道以下代码中内存/变量的行为如何。基本上，我使用 epd_power_on() 将 epd_tx_buffer 添加到 epd_driver_state 中的数组中。

然后这些缓冲区通过事件驱动机制异步消耗/使用。我担心/我想知道的是，“uint8_t * buffer”指向的内存区域的内容是否是常量，或者是否有可能被覆盖。当 epd_power_on 完成时，将会执行其他代码，直到异步事件消耗缓冲区。

struct epd_tx_buffer {
    uint8_t hasCmd;
    uint8_t * buffer;
    uint16_t bufferLen;
    uint8_t wait_ms;
};

static struct epd_driver_state {
    uint8_t cursor;
    uint8_t length;
    struct epd_tx_buffer buff[256];
    bool isRunning;
} epd_driver_state;

static void epd_power_on(void){
    addToSPIQueueCommandData( ( uint8_t[] ) { POWER_ON }, 1 );
    addToSPIQueueCommandData( ( uint8_t[] ) { PANEL_SETTING, 0x2F }, 2 );
    addToSPIQueueCommandData( ( uint8_t[] ) { PLL_CONTROL, 0x3A }, 2 );
    addToSPIQueueCommandData( ( uint8_t[] ) { POWER_SETTING, 0x03, 0x00, 0x2B, 0x2B, 0x09 }, 6 );
    addToSPIQueueCommandData( ( uint8_t[] ) { BOOSTER_SOFT_START, 0x07, 0x07, 0x17  }, 4);
    addToSPIQueueCommandData( ( uint8_t[] ) { VCM_DC_SETTING_REGISTER, 0x00 }, 2 );
    addToSPIQueueCommandData( ( uint8_t[] ) { VCOM_AND_DATA_INTERVAL_SETTING, 0x47 }, 2 );
}



bool addToSPIQueueCommandData(uint8_t * buffer, uint16_t bufferLen)
{
    if( epd_driver_state.length >= 255 ) return false;
    epd_driver_state.buff[ epd_driver_state.length ].hasCmd         = 1;
    epd_driver_state.buff[ epd_driver_state.length ].buffer         = buffer;
    epd_driver_state.buff[ epd_driver_state.length ].bufferLen      = bufferLen;
    epd_driver_state.length++;
    return true;
}

一些解释将不胜感激!

Answer 1

addToSPIQueueCommandData( ( uint8_t[] ) { POWER_ON }, 1 );
addToSPIQueueCommandData( ( uint8_t[] ) { PANEL_SETTING, 0x2F }, 2 );
addToSPIQueueCommandData( ( uint8_t[] ) { PLL_CONTROL, 0x3A }, 2 );
addToSPIQueueCommandData( ( uint8_t[] ) { POWER_SETTING, 0x03, 0x00, 0x2B, 0x2B, 0x09 }, 6 );
addToSPIQueueCommandData( ( uint8_t[] ) { BOOSTER_SOFT_START, 0x07, 0x07, 0x17  }, 4);
addToSPIQueueCommandData( ( uint8_t[] ) { VCM_DC_SETTING_REGISTER, 0x00 }, 2 );
addToSPIQueueCommandData( ( uint8_t[] ) { VCOM_AND_DATA_INTERVAL_SETTING, 0x47 }, 2 );

这些是数组复合文字，一旦控制退出函数，它们就会超出范围。因此，在函数外部使用引用访问它们是未定义的行为。

<小时/>

您可以考虑按如下方式进行操作。

uint8_t *temp = malloc(sizeof((( uint8_t[] ) { PLL_CONTROL, 0x3A })));
memcpy(temp, (( uint8_t[] ) { PLL_CONTROL, 0x3A }), 2);
addToSPIQueueCommandData(temp, 2);

Note: Make sure you free the memory once done processing.