将16位变量存储到解引用变量写入32位

Question

Consider the following:

// main.h
struct
{
    uint16_t aChargeOption0;
    uint16_t aChargeOption1;
} oBattChargerInfo;

typedef struct CHGRRM
{
    uint16_t nRegIndex;
    uint8_t  nDataType;
    uint32_t nDataWidth;
    uint32_t nRegAddress;
    bool     IsWritable;
    bool     HasBits;
    uint32_t nBitStoreStart;
        uint32_t nBitStoreEnd;
    int  *ptrToData;
} chargerRegMap_t;

extern chargerRegMap_t charger_reg_map[];



// main.c

chargerRegMap_t charger_reg_map[] =
{
  { &oBattChargerInfo.aChargeOption0 },
  { &oBattChargerInfo.aChargeOption1 },
};




// code to store a variable to the de-referenced variable
uint16_t aFinalBuff=0x00;
aFinalBuff=buff[1]<<8;     // buff[0] and buff[1] is uint8 
aFinalBuff=aFinalBuff+buff[0];
*charger_reg_map[nRegIndex].ptrToData=aFinalBuff;

When I store the first variable ( charger_reg_map[0].ptrToData which in the first case is oBattChargerInfo.aChargeOption0 ) the 16 bit variable overwrites the adjacent variable oBattChargerInfo.aChargeOption1 . Other than setting each variable in my oBattChargerInfo structure to 32 bits each, is there another solution? It seems strange that a dereferenced variable would work this way.

I tried *charger_reg_map[nRegIndex].ptrToData=(uint16_t)aFinalBuff; to make clear my intention. Didn't matter.

What am I doing wrong here?

Answer 1

If you want differently-sized variables, there is no pointer type you can use to write to all of them.

The design is a bit brittle, since you would need to know which member your pointer is pointing to, or at least its type.

I think a better option would be to do the work with memcpy through a function, and add a 'size' member to chargerRegMap_t for sanity checking.

Something like

void write_data(chargerRegMap_t* map, void* data, size_t size)
{
    assert(size == map->data_size);
    memcpy(map->ptrToData, data, size);
}

/* ... */
uint16_t aFinalBuff = 0x00;
aFinalBuff = buff[1] << 8; 
aFinalBuff = aFinalBuff + buff[0];
write_data(charger_reg_map + nRegIndex, &aFinalBuff, sizeof(aFinalBuff));  

I would probably add a macro to that as well, to eliminate sizeof typos and make it less tedious:

#define WRITE_DATA(map, data) write_data(map, &data, sizeof(data))
/* ... */
WRITE_DATA(charger_reg_map + nRegIndex, aFinalBuff);