How to read and write arrays of bytes on serial port in C/C++

Introduction

This page explains how to read and write arrays of bytes using the Serialib library. Serialib is a cross-platform library written in C++.

No dependencies
Only two files (serialib.h and serialib.cpp)
Cross-platform

The library has been tested on Windows and Linux. This project has been developed with Qt Creator and succesfully compile with:

gcc on Linux
MinGW on Windows The library should work on Mac OS and be compiled with others IDE.

rightBytes

int serialib::writeBytes(const void *Buffer, const unsigned int NbBytes)

The Serialib class has a writeBytes() method that expect two parameters:

Buffer is an array of bytes containing at least NbBytesbytes
NbBytes is the number of bytes to transmit

writeString() return an integer:

1 in case of success
-1 if an error happened while sending the strings

readBytes

int serialib::readBytes ( void *buffer,
                          unsigned int maxNbBytes,
                          unsigned int timeOut_ms, 
                          unsigned int sleepDuration_us);

The readBytes() method reads an array of maxNbBytes bytes on the serial device. This method expects two mandatory and two optional parameters:

buffer is the array where populated by the function with the read bytes. Note that memory allocation must be large enough to store the bytes.
maxNbBytes is the maximum number of bytes read. When then number of bytes read is equal to maxNbBytes, the function exits.
timeOut_ms [optional] is the time out in milliseconds. When the timeout is over, the function returns the populated array and exit. If the timeout is set to zéro or not set, time out is disabled.
sleepDuration_us[optional] is the delay of CPU relaxing in microseconds (Linux only). After everytime the function try to read data on the serial device, the CPU is relaxed to perfom other task (thread for example).

The function returns the number of bytes read when succesfull.

If a problem happens, the function returns one of the following values:

0 timeout is reached
-1 error while setting the Timeout
-2 error while reading the bytes

Example

The following example send an array of 8 bytes. And then try to read 8 bytes on the serial device. This example has been tested with an Arduino that returns each byte received multiply by two. Download the full example on Github.

// Serial object
serialib serial;

// Connection to serial port
char errorOpening = serial.openDevice(SERIAL_PORT, 115200);

// If connection fails, return the error code otherwise, display a success message
if (errorOpening!=1) return errorOpening;
printf ("Successful connection to %s\n",SERIAL_PORT);

// Create an array of bytes
unsigned char prime[8] = { 1, 3, 5, 7, 11, 13, 17, 19 };

// Write the array on the serial device
serial.writeBytes(prime, 8);
printf ("Data sent\n");

// Read the bytes
unsigned char received[8];
serial.readBytes(received, 8, 2000, 1000);

// Display each byte received
for (int i=0; i<8 ; i++)
    printf("Receive [%d] = %d\n", i, received[i]);

// Close the serial device
serial.closeDevice();

return 0 ;

Arduino code

Here is the Arduino code used for checking the example:

// Setup, initialize
void setup() {
  Serial.begin(115200);
}

// Loop forever
void loop() {
  // If serial data is pending, read, write twice the received byte
  if (Serial.available())
    Serial.write( 2*Serial.read() );
}

Output

If everything is fine, the C code should display something like:

Successful connection to /dev/ttyACM0
Data sentReceive [0] = 2
Receive [1] = 6
Receive [2] = 10
Receive [3] = 14
Receive [4] = 22
Receive [5] = 26
Receive [6] = 34
Receive [7] = 38