將32位長分成4個字節

Question

我知道有很多這方面的例子，但是他們都沒有工作。 PPTR是一個指向這種類型

typedef struct 
{ 
    TIMESTAMP_TYPE oTimeStamp; 
    ASSERT_ID_TYPE ucAssertID; 
    Int16 iData1; 
    Int16 iData2; 
    UInt16 uiChecksum; 
} 
LOG_ENTRY_TYPE; 

，我出列，我的日誌時，有一個我想關店到EEEPROM的臨時日誌。
oTimestamp的類型是

typedef struct 
{ 
    UInt32 ulSecond; 
    UInt16 usMilliSecond; 
    UInt16 usPowerCycleCount; 

} 
    TIMESTAMP_TYPE; 

所有其他的訪問，甚至可用於毫秒寫入工作，但我不能細分爲4個字節秒時間戳值。

這是我曾嘗試（很明顯，只有一個版本的註釋去掉了）：

UChar tmpByteHigh; 
UChar tmpByteLow; 

//Attempt1 
tmpByteHigh = (pPtr->oTimeStamp.ulSecond >> 24) & 0x000000FF; 
SPIwrite(tmpByteHigh); 
tmpByteLow = (pPtr->oTimeStamp.ulSecond >> 16) & 0x000000FF; 
SPIwrite(tmpByteLow); 
tmpByteHigh = (pPtr->oTimeStamp.ulSecond >> 8) & 0x000000FF; 
SPIwrite(tmpByteHigh); 
tmpByteLow = (pPtr->oTimeStamp.ulSecond) & 0x000000FF; 
SPIwrite(tmpByteLow); 

//Attempt 2 
tmpByteHigh = (pPtr->oTimeStamp.ulSecond & 0xFF000000UL) >> 24; 
SPIwrite(tmpByteHigh); 
tmpByteLow = (pPtr->oTimeStamp.ulSecond & 0x00FF0000UL) >> 16; 
SPIwrite(tmpByteLow); 
tmpByteHigh = (pPtr->oTimeStamp.ulSecond & 0x0000FF00UL) >> 8; 
SPIwrite(tmpByteHigh); 
tmpByteLow = (pPtr->oTimeStamp.ulSecond) & 0x000000FFUL; 
SPIwrite(tmpByteLow); 


//Attempt 3 
//get msw from 32 bit value and write the 2 msB from it 
tmpWord = (pPtr->oTimeStamp.ulSecond >> 16) & 0x0000FFFF; 
tmpByteHigh = (tmpWord >> 8) & 0x00FF; 
SPIwrite(tmpByteHigh); 
tmpByteLow = tmpWord & 0x00FF; 
SPIwrite(tmpByteLow); 
//get lsw from 32 bit value and write the 2 lsB from it 
tmpWord = pPtr->oTimeStamp.ulSecond & 0x0000FFFF; 
tmpByteHigh = (tmpWord >> 8) & 0x00FF; 
SPIwrite(tmpByteHigh); 
tmpByteLow = tmpWord & 0x00FF; 
SPIwrite(tmpByteLow); 


//Attempt 4 
UChar* myPointer = (UChar*)&pPtr->oTimeStamp.ulSecond; 
UChar myArray[4]; 
myArray[0]=myPointer[0]; 
myArray[1]=myPointer[1]; 
myArray[2]=myPointer[2]; 
myArray[3]=myPointer[3]; 
SPIwrite(myArray[0]); 
SPIwrite(myArray[1]); 
SPIwrite(myArray[2]); 
SPIwrite(myArray[3]); 

每一次我得到0×00 0×00 0×00 0x80的送過來SPI。有什麼想法嗎？對我來說簡單我不是一個優秀的程序員。

Answer 1

使用union，你可以以多種方式訪問​​相同的數據：

typedef union 
{ 
    struct { 
     UInt32 ulSecond; 
     UInt16 usMilliSecond; 
     UInt16 usPowerCycleCount; 
    }; 
    UInt8 byte[8]; 
} 
TIMESTAMP_TYPE; 

int main() { 
    TIMESTAMP_TYPE T; 
    T.ulSecond = 1; 
    T.usMilliSecond = 2; 
    T.usPowerCycleCount = 3; 
    printf("sizeof(T) = %ld\n", sizeof(T)); 
    for(int i = 0; i < 8; i++) 
     printf("T[%d] = 0x%2.2X\n", i, T.byte[i]); 
    return 0; 
} 

打印：

sizeof(T) = 8 
T[0] = 0x01 
T[1] = 0x00 
T[2] = 0x00 
T[3] = 0x00 
T[4] = 0x02 
T[5] = 0x00 
T[6] = 0x03 
T[7] = 0x00 

要注意的是字節數組有本地endianness。如果這不是所需的字節順序，你將不得不交換字節。