C 结构体成员不存储分配的值

Question

我正在使用微处理器（PIC32MX250），并且创建了一个存储各种成员的结构：

typedef struct {
    char element1[20];
    unsigned char element2;
    unsigned char element3[2];
    unsigned char element4[2];
    unsigned char element5[2];
    unsigned char element6[2];
    unsigned char element7;
    unsigned char element8;
    unsigned char element9[2];
    unsigned char element10;
    unsigned char element11[2];
    unsigned char element12;
    char element13[7];
    unsigned char service_day;
    unsigned char service_month;
    unsigned char service_year;
    unsigned char service_hour;
    unsigned char service_minute;
    unsigned char service_status[2];
} usb_service_t;

然后我调用一个函数来读取闪存内的元素并将它们传输到该结构，如下所示：

usb_service_t g_service_container;
void read_service (unsigned int memory_address)
{
    byte loop_idx = 0;
    byte buf[64] = { 0 };

    (void) Flash_Read(memory_address, buf, 64, 0);

    g_service_container.service_day= buf[0]; // <<< PROBLEM HERE

    g_service_container.service_month= buf[1];
    g_service_container.service_year= buf[2];
    g_service_container.service_hour= buf[3];
    g_service_container.service_minute= buf[4];
    for (loop_idx = 0; loop_idx < 20; loop_idx++)
    {
        g_service_container.targa[loop_idx] = buf[5 + loop_idx];   
        if (g_service_container.element1[loop_idx] == 0x8e)
        {
            g_service_container.element1[loop_idx] = 'A';
        }
        else if (g_service_container.element1[loop_idx] == 0x99)
        {
            g_service_container.element1[loop_idx] = 'O';
        }
        else if (g_service_container.element1[loop_idx] == 0x9a)
        {
            g_service_container.element1[loop_idx] = 'U';
        }
    }
    g_service_container.element1[20] = '\0';
    g_service_container.element2= buf[25];
    for (loop_idx = 0; loop_idx < 2; loop_idx++)
    {
        g_service_container.element3[loop_idx] = buf[26 + 1 - loop_idx];
        g_service_container.element4[loop_idx] = buf[28 + 1 - loop_idx];
        g_service_container.element5[loop_idx] =
                                                    buf[30 + 1 - loop_idx];
        g_service_container.element6[loop_idx] = buf[32 + 1 - loop_idx];
        g_service_container.element9[loop_idx] = buf[36 + 1 - loop_idx];
        g_service_container.service_status[loop_idx] = buf[38 + 1 - loop_idx];
        g_service_container.element11[loop_idx] =
                                                    buf[41 + 1 - loop_idx];
    }
    g_service_container.element7= buf[34];
    g_service_container.element8= buf[35];
    g_service_container.element10= buf[40];
    g_service_container.element12= buf[43];
    for (loop_idx = 0; loop_idx < 7; loop_idx++)
    {
        g_service_container.element13[loop_idx] = buf[44 + loop_idx];
    }
    g_service_container.element13[7] = '\0';

}

当我从结构体成员的缓冲区，我可以使用 MPLAB 调试器看到，g_service_container.service_day 始终为 0，特别是 buf[0] 不为零（其他人则读取缓冲区值）。

我试图强制成员的值写入一个常量值并且它接受它。

然而以不同的方式编写结构，如下所示，它可以工作：

typedef struct {
    char element1[20];
    unsigned char element2;
    unsigned char element3[2];
    unsigned char element4[2];
    unsigned char element5[2];
    unsigned char element6[2];
    unsigned char element7;
    unsigned char element8;
    unsigned char element9[2];
    unsigned char element10;
    unsigned char element11[2];
    unsigned char element12;
    char element13[7];
    unsigned char service_status[2];  // NOW I CHANGE THE ORDER OF THIS MEMBER
    unsigned char service_day;
    unsigned char service_month;
    unsigned char service_year;
    unsigned char service_hour;
    unsigned char service_minute;
} usb_service_t;

Answer 1

听起来编译器正在填充结构。请参阅这篇文章了解其工作原理：https://stackoverflow.com/a/40642888/9766462