How to sprintf with uint8_t array? - c

Question

The main problem is that actually I have a uint8_t* data buffer. It an array and I only know Its size and Its pointer.
I want to sprintf the data from this pointer in a buffer like this :
void send_bin(uint8_t* binarypayload, uint8_t size, uint32_t mode)
{
char buffer[256];
sprintf(buffer, "AT+ZF=%s,%lu\r\n", binarypayload, mode);
HAL_UART_Transmit(&husart1, (uint8_t*)buffer, strlen((char*) buffer), 1000);
}
But on my uart I can only see the binary value on my uart:
þTÞ­˜.
Where am I going wrong ?
Sorry I have forgotten to say that my datas is like :
uint8_t buffer[4] = {0x45, 0xAD, 0xEF, 0x5B};
And I want it to look like this on my uart :
AT+ZF=45ADEF5B,45
but I only have access to its pointer

Answer 1

You need to convert the binary data into a hexadecimal format. The easiest way, is to convert each byte individually:
void send_bin(uint8_t* binarypayload, uint8_t size, uint32_t mode)
{
char buffer[256];
strcpy(buffer, "AT+ZF=");
for (int i = 0; i < size; i++) {
sprintf(buffer + strlen(buffer), "%02x", binarypayload[i]);
}
sprintf(buffer + strlen(buffer), ",%lud\r\n", mode);
HAL_UART_Transmit(&husart1, (uint8_t*)buffer, strlen(buffer), 1000);
}

Answer 2

snprintf can convert the bytes into their hexadecimal format in a string, but it doesn't have the automatic ability to do that to an array of them. We can call it multiple times in a for loop to enable that ability though.
void send_bin(uint8_t* binarypayload, uint8_t size, uint32_t mode) {
char buffer[256] = {};
int offset = 0;
int ret = snprintf(buffer + offset, sizeof(buffer) - offset,
"AT+ZF=");
assert(ret == 6);
offset += ret;
for (int i = 0; i < size; i++) {
ret = snprintf(buffer + offset, sizeof(buffer) - offset;
"%02X", binarypayload[i]);
assert(ret == 2);
offset += ret;
}
ret = snprintf(buffer + offset, sizeof(buffer) - offset,
"\r\n");
assert(ret == 2);
HAL_UART_Transmit(&husart1, (uint8_t*)buffer, strlen((char*) buffer), 1000);
}

Answer 3

sprintf on uC for this simple task is overkill. And it will not work if you decide to use RTOS in your project.
I would:
const char digits[] = "0123456789ABCDEF";
char *dumphex(char *buff, const void *data, size_t size)
{
char *wrk = buff;
const uint8_t *u8data = data;
if(buff && data)
{
while(size--)
{
*wrk++ = digits[*u8data >> 4];
*wrk++ = digits[*u8data & 0x0f];
}
*wrk = 0;
}
return buff;
}
or if you do not want to use lookup string
#define GETDIGIT(x) ((x) > 9 ? ((x) - 10) + 'A' : (x) + '0')
char *dumphex1(char *buff, const void *data, size_t size)
{
char *wrk = buff;
const uint8_t *u8data = data;
if(buff && data)
{
while(size--)
{
*wrk++ = GETDIGIT(*u8data >> 4);
*wrk++ = GETDIGIT(*u8data & 0x0f);
}
*wrk = 0;
}
return buff;
}