如何将uint8_t从uart_read_bytes转换为char或可以添加到cJSON对象的内容？

Question

Here I am reading from a UART that is communicating with another device that is sending it bytes. If I am getting an integer value in 3 bytes, how best to convert it to something I can send using cJSON. I can get the value and iterate over it, but once I put it in a char array, i cannot even see the value any longer. Thoughts?

{
  uint8_t buf[BUF_SIZE];
  memset(buf, 0, sizeof(buf));
  // Read data from the UART
  int checkIt = uart_write_bytes(UART_NUM_2, (const char *)hex, 
  strlen(hex));
  ESP_LOGI(LOG_TAG, "this is the length of transmit: %i: ", checkIt);
   int len2 = uart_read_bytes(UART_NUM_2, buf, BUF_SIZE - 1, 1000 
  portTICK_RATE_MS);

  ParseData(buf);

}

 ParseData(char * data)
{
 //initialize char array to zeros
 char temporary[4] = {0};

 for(int i=0; i<3; i++)
 {
  //first two bytes are not needed, so skip them for now
   temporary[i] = data[i+2];
   ESP_LOGI(LOG_TAG, " temporary # %i %i ", i, temporary[i]);
 }
temporary[3] = '\0';
ESP_LOGI(LOG_TAG, " temp char contents update %s ", temporary;

}

The for loop will show me each of the values, like 1, 2, 3 (individual integers sent as individual bytes, not a string and not '1', '2', '3' - but I wan't to combine it into 123 which is why I setup the temporary array. It is printing out nothing, even if I don't add the null character to it. If I can get it to a single value (123), or even a char (string type), then I can add it to a cJSON object and send it.

Answer 1

If the line:

ESP_LOGI(LOG_TAG, " temporary # %i %i ", i, temporary[i]);

is indicating integer values 1, 2, 3 then the data is integer data not character data. To represent the data as a string of decimal digit characters change:

temporary[i] = data[i+2];

to

temporary[i] = '0' + data[i+2];

However it seems unlikely that the data is intended to be interpreted in that manner - it is a very inefficient and wasteful method of transferring integer data. Are you sure that he data is not in fact a single 24 bit integer, where rather then the loop and array, you in fact need:

int value = data[2] << 16 | data[3] << 8 | data[4] ;

or

int value = data[4] << 16 | data[3] << 8 | data[2] ;

depending on the byte order of the data?

Answer 2

So, it appears that for my situation, I am converting individual bytes read from a UART to an integer

char data[3]  = {0};
data[0] = 0x01
data[1] = 0x02
data[2] = 0x03

ParseData(data);

void ParseData(uint8_t * data)
{
    uint32_t val = (data[0] * 100) + (data[1] * 10) + data[2];
    ESP_LOGI(LOG_TAG, " val # %i ", val);
}