Modbus library for modern C++

Library for high level Modbus frame/packet manipulation, including encoding and decoding, all written in modern C++17.

that you can use as a starting point for you application ! Until there will some reliable way to test it, it will be treated as such.

Table of content

• Why
• Important Concept
• Possibilities
• Dependencies
• Installation

Why

When I was working on my last project and tried to find a good C++ Modbus library (other than Qt) I was unable to find it. That is why I have decided to share my own implementation of Modbus.

Important Concept

This library is mainly for providing Modbus logic. It doesnt aim to have best communication implementation, as it is usually HW-specific. It gives user ability to create Modbus frames using high level api and convert them to raw bytes or show them as string. That is why Modbus Core is OS independent and can be easily used with other communication frameworks, assuming that you compiler supports at least C++17.

Modbus communiaction module is enabled by default and works pretty well on linux. If you are using your own communication, be sure to disable it via cmake variable.

Possibilities

Quick example of what Modbus Core can do:

Code:

#include "MB/modbusException.hpp"
#include "MB/modbusRequest.hpp"
#include "MB/modbusResponse.hpp"

// Create simple request
MB::ModbusRequest request(1, MB::utils::ReadDiscreteOutputCoils, 100, 10);

std::cout << "Stringed Request: " << request.toString() << std::endl;

std::cout << "Raw request:" << std::endl;

// Get raw represenatation for request
std::vector<uint8_t> rawed = request.toRaw();

// Method for showing byte
auto showByte = [](const uint8_t &byte) {
    std::cout << " 0x" << std::hex << std::setw(2) << std::setfill('0')
                << static_cast<int>(byte);
};

// Show all bytes
std::for_each(rawed.begin(), rawed.end(), showByte);
std::cout << std::endl;

// Create CRC and pointer to its bytes
uint16_t CRC = MB::utils::calculateCRC(rawed);
auto CRCptr  = reinterpret_cast<uint8_t *>(&CRC);

// Show byted CRC for request
std::cout << "CRC for the above code: ";
std::for_each(CRCptr, CRCptr + 2, showByte);
std::cout << std::endl;

auto request1 = MB::ModbusRequest::fromRaw(rawed);
std::cout << "Stringed Request 1 after rawed: " << request1.toString() << std::endl;

// Add CRC to the end of raw request so that it can be loaded with CRC check
rawed.insert(rawed.end(), CRCptr, CRCptr + 2);
auto request2 = MB::ModbusRequest::fromRawCRC(rawed); // Throws on invalid CRC
std::cout << "Stringed Request 2 after rawed: " << request2.toString() << std::endl;

Output:

Stringed Request: Read from output coils, from slave 1, starting from address 100, on 10 registers
Raw request:
 0x01 0x01 0x00 0x64 0x00 0x0a
CRC for the above code:  0xfd 0xd2
Stringed Request 1 after rawed: Read from output coils, from slave 1, starting from address 100, on 10 registers
Stringed Request 2 after rawed: Read from output coils, from slave 1, starting from address 100, on 10 registers

Dependencies

Library core is dependency free - except for C++ standard library.

For communication module, you may need:

• libnet - only for tcp communication (not needed if communication is disabled)

How to learn Modbus ?

Just use Simply modbus.

How to install it ?

First go to directory that will contain this library.

git clone AbdelrahmanOKAsh/Modbus_ModernCppProject
cd Build && make