试图将struct成员复制到c中的字节数组

Question

我试图将包含int,char和char数组的结构的成员复制到字节数组中以发送到串行线.到目前为止我有

struct msg_on_send
{
    char descriptor_msg[5];
    int  address;
    char space;
    char cmdmsg[5];
    char CR;
    char LF;
};

void switch_output_on()
{
    int member;
    struct msg_on_send SendMsg_on[sizeof member] =
     {

    };
    unsigned char buffer [ sizeof SendMsg_on[0] ];
    showbytes(buffer, serialize(buffer, SendMsg_on));
}

/*************************************************************************** 
*   Function:   ArrayBuild                                                 *
*   Purpose:    Uses memcopy to transfer the struct members sequentially   *
*               into an array of char                                      *
*   Arguments:                                                             *
*   Returns:    size_t i = a count of the number of bytes in the array     *
***************************************************************************/    

size_t ArrayBuild(unsigned char *dst, const struct msg_on_send *object)
{
    size_t i = 0;

    memcpy(&dst[i], &object->descriptor_msg, sizeof object->descriptor_msg);
    i += sizeof object->descriptor_msg;

    memcpy(&dst[i], &object->address, sizeof object->address);
    i += sizeof object->address;

    memcpy(&dst[i], &object->space, sizeof object->space);
    i += sizeof object->space;

    memcpy(&dst[i], &object->cmdmsg, sizeof object->cmdmsg);
    i += sizeof object->cmdmsg;

    memcpy(&dst[i], &object->CR, sizeof object->CR);
    i += sizeof object->CR;

    memcpy(&dst[i], &object->LF, sizeof object->LF);
    i += sizeof object->LF;

    return i;
}

/*********************************************************************** 
*   Function:   USARTWrite                                             *
*   Purpose:    Writes the array data to the USART data register       *
*   Arguments:  void *object = struct member                           *
*               size_t size =  size of array remaining                 *
*   Returns:    None                                                   *
***********************************************************************/

void USARTWrite(const void *object, size_t size)        
{
    const unsigned char *byte;
    for ( byte = object; size--; ++byte )
    {
        printf("%02X", *byte);
    }
    putchar('\n');
}

当我获得此代码时,我不完全理解它是如何工作的.我可以看到memcpy接受结构的每个元素并使其成为由'i'变量索引的串行流,但我不知道USARTWrite函数如何将其分组为字符串,或者如何加载数组我的结构初始化.

对不起,这篇文章有点长,但我刚刚开始编程,并试图了解这个概念.

谢谢戴夫

编辑:

哇,很快就有很多好的答案 - 谢谢你们.

slaz:这对我来说似乎是合乎逻辑的,我还没有真正考虑过这种方法,因为我还没有真正掌握指针,但我开始看到它们是C的重要组成部分,所以我真的会有看看.

• 这行代码将数据发送到我的UART,我将用包含消息内容的数组替换？看起来我错过了一个合乎逻辑的步骤,我有一个变量告诉我我的结构在哪里开始,它有多大,但没有数组要发送

  USART_SendData(USART1, message_on_contents[array_count]);
  

哈珀谢尔比:谢谢你的描述,让我的想法更加清晰.

RGDS

戴夫

Answer 1

您不必将结构实际复制到字节数组中.你可以选择这样做:

struct msg_on_send myMessage;

// code to set myMessage to whatever values...

// get a byte pointer that points to the beginning of the struct    
uint8_t *bytePtr = (uint8_t*)&myMessage;

// pass that into the write function, and it will write the amount of bytes passed in
USARTWrite(bytePtr, sizeof(myMessage));

指针的力量!:)

Answer 2

对不起,直到现在我才看到你的评论.下面的代码在Linux上编译就好了,所以我希望它适合你.
printf()以十六进制打印,每个字节将获得2个字符.

#include <stdio.h>

struct msg_on_send
{
char descriptor_msg[5];
int  address;
char space;
char cmdmsg[5];
char CR; 
char LF; 
};

void USARTWrite(const void *object, size_t size)    
{
    const unsigned char *byte;
      for ( byte = object; size--; ++byte )                                     
      {   
          printf("%02X", *byte);
      }   
      putchar('\n');
}

int main (int argc, char**argv)
{
    struct msg_on_send myMsg;
    unsigned char* ptr= (unsigned char*)&myMsg;

    USARTWrite(ptr, sizeof(myMsg));

    return 0;
}

我希望这有帮助.

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