Comparing an usart received uint8_t* data with a constant string - c++

Question

I'm working on an Arduino Due, trying to use DMA functions as I'm working on a project where speed is critical. I found the following function to receive through serial:
uint8_t DmaSerial::get(uint8_t* bytes, uint8_t length) {
// Disable receive PDC
uart->UART_PTCR = UART_PTCR_RXTDIS;
// Wait for PDC disable to take effect
while (uart->UART_PTSR & UART_PTSR_RXTEN);
// Modulus needed if RNCR is zero and RPR counts to end of buffer
rx_tail = (uart->UART_RPR - (uint32_t)rx_buffer) % DMA_SERIAL_RX_BUFFER_LENGTH;
// Make sure RPR follows (actually only needed if RRP is counted to the end of buffer and RNCR is zero)
uart->UART_RPR = (uint32_t)rx_buffer + rx_tail;
// Update fill counter
rx_count = DMA_SERIAL_RX_BUFFER_LENGTH - uart->UART_RCR - uart->UART_RNCR;
// No bytes in buffer to retrieve
if (rx_count == 0) { uart->UART_PTCR = UART_PTCR_RXTEN; return 0; }
uint8_t i = 0;
while (length--) {
bytes[i++] = rx_buffer[rx_head];
// If buffer is wrapped, increment RNCR, else just increment the RCR
if (rx_tail > rx_head) { uart->UART_RNCR++; } else { uart->UART_RCR++; }
// Increment head and account for wrap around
rx_head = (rx_head + 1) % DMA_SERIAL_RX_BUFFER_LENGTH;
// Decrement counter keeping track of amount data in buffer
rx_count--;
// Buffer is empty
if (rx_count == 0) { break; }
}
// Turn on receiver
uart->UART_PTCR = UART_PTCR_RXTEN;
return i;
}
So, as far as I understand, this function writes to the variable bytes, as a pointer, what is received as long as is no longer than length. So I'm calling it this way:
dma_serial1.get(data, 8);
without assigning its returning value to a variable. I'm thinking the received value is stored to the uint8_t* data but I might be wrong.
Finally, what I want to do is to check if the received data is a certain char to take decisions, like this:
if (data == "t"){
//do something//}
How could I make this work?

Answer 1

For comparing strings like intended by if (data == "t"), you'll need a string comparison function like, for example, strcmp. For this to work, you must ensure that the arguments are actually (0-terminated) C-strings:
uint8_t data[9];
uint8_t size = dma_serial1.get(data, 8);
data[size]='\0';
if (strcmp(data,"t")==0) {
...
}
In case that the default character type in your environment is signed char, to pass data directly to string functions, a cast is needed from unsigned to signed:
if (strcmp(reinterpret_cast<const char*>(data),"t")==0) {
...
}
So a complete MVCE could look as follows:
int get(uint8_t *data, int size) {
data[0] = 't';
return 1;
}
int main()
{
uint8_t data[9];
uint8_t size = get(data, 8);
data[size]='\0';
if (strcmp(reinterpret_cast<const char*>(data),"t")==0) {
cout << "found 't'" << endl;
}
}
Output:
found 't'