Category: Computer Programming

Solidity – Style Guide ”; Previous Next Style Guide helps to maintain code layout consistent and make code more readable. Following are the best practices following while writing contracts with Solidity. Code Layout Indentation − Use 4 spaces instead of tab to maintain indentation level. Avoid mixing spaces with tabs. Two Blank Lines Rule − Use 2 Blank lines between two contract definitions. pragma solidity ^0.5.0; contract LedgerBalance { //… } contract Updater { //… } One Blank Line Rule − Use 1 Blank line between two functions. In case of only declaration, no need to have blank lines. pragma solidity ^0.5.0; contract A { function balance() public pure; function account() public pure; } contract B is A { function balance() public pure { // … } function account() public pure { // … } } Maximum Line Length − A single line should not cross 79 characters so that readers can easily parse the code. Wrapping rules − First argument be in new line without opening parenthesis. Use single indent per argument. Terminating element ); should be the last one. function_with_a_long_name( longArgument1, longArgument2, longArgument3 ); variable = function_with_a_long_name( longArgument1, longArgument2, longArgument3 ); event multipleArguments( address sender, address recipient, uint256 publicKey, uint256 amount, bytes32[] options ); MultipleArguments( sender, recipient, publicKey, amount, options ); Source Code Encoding − UTF-8 or ASCII encoding is to be used preferably. Imports − Import statements should be placed at the top of the file just after pragma declaration. Order of Functions − Functions should be grouped as per their visibility. pragma solidity ^0.5.0; contract A { constructor() public { // … } function() external { // … } // External functions // … // External view functions // … // External pure functions // … // Public functions // … // Internal functions // … // Private functions // … } Avoid extra whitespaces − Avoid whitespaces immediately inside parenthesis, brackets or braces. Control structures − Braces should open on same line as declaration. Close on their own line maintaining the same indentation. Use a space with opening brace. pragma solidity ^0.5.0; contract Coin { struct Bank { address owner; uint balance; } } if (x < 3) { x += 1; } else if (x > 7) { x -= 1; } else { x = 5; } if (x < 3) x += 1; else x -= 1; Function Declaration − Use the above rule for braces. Always add a visibility label. Visibility label should come first before any custom modifier. function kill() public onlyowner { selfdestruct(owner); } Mappings − Avoid whitespaces while declaring mapping variables. mapping(uint => uint) map; mapping(address => bool) registeredAddresses; mapping(uint => mapping(bool => Data[])) public data; mapping(uint => mapping(uint => s)) data; Variable declaration − Avoid whitespaces while declaring array variables. uint[] x; // not unit [] x; String declaration − Use double quotes to declare a string instead of single quote. str = “foo”; str = “Hamlet says, ”To be or not to be…””; Order of Layout Elements should be layout in following order. Pragma statements Import statements Interfaces Libraries Contracts Within Interfaces, libraries or contracts the order should be as − Type declarations State variables Events Functions Naming conventions Contract and Library should be named using CapWords Style. For example, SmartContract, Owner etc. Contract and Library name should match their file names. In case of multiple contracts/libraries in a file, use name of core contract/library. Owned.sol pragma solidity ^0.5.0; // Owned.sol contract Owned { address public owner; constructor() public { owner = msg.sender; } modifier onlyOwner { //…. } function transferOwnership(address newOwner) public onlyOwner { //… } } Congress.sol pragma solidity ^0.5.0; // Congress.sol import “./Owned.sol”; contract Congress is Owned, TokenRecipient { //… } Struct Names − Use CapWords Style like SmartCoin. Event Names − Use CapWords Style like Deposit, AfterTransfer. Function Names − Use mixedCase Style like initiateSupply. Local and State variables − Use mixedCase Style like creatorAddress, supply. Constants − Use all capital letters with underscore to seperate words like MAX_BLOCKS. Modifier Names − Use mixCase Style like onlyAfter. Enum Names − Use CapWords Style like TokenGroup. Print Page Previous Next Advertisements ”;

Solidity – Comments ”; Previous Next Solidity supports both C-style and C++-style comments, Thus − Any text between a // and the end of a line is treated as a comment and is ignored by Solidity Compiler. Any text between the characters /* and */ is treated as a comment. This may span multiple lines. Example The following example shows how to use comments in Solidity. function getResult() public view returns(uint){ // This is a comment. It is similar to comments in C++ /* * This is a multi-line comment in solidity * It is very similar to comments in C Programming */ uint a = 1; uint b = 2; uint result = a + b; return result; } Print Page Previous Next Advertisements ”;

Solidity – Strings ”; Previous Next Solidity supports String literal using both double quote (“) and single quote (”). It provides string as a data type to declare a variable of type String. pragma solidity ^0.5.0; contract SolidityTest { string data = “test”; } In above example, “test” is a string literal and data is a string variable. More preferred way is to use byte types instead of String as string operation requires more gas as compared to byte operation. Solidity provides inbuilt conversion between bytes to string and vice versa. In Solidity we can assign String literal to a byte32 type variable easily. Solidity considers it as a byte32 literal. pragma solidity ^0.5.0; contract SolidityTest { bytes32 data = “test”; } Escape Characters Sr.No. Character & Description 1 n Starts a new line. 2 \ Backslash 3 ” Single Quote 4 “ Double Quote 5 b Backspace 6 f Form Feed 7 r Carriage Return 8 t Tab 9 v Vertical Tab 10 xNN Represents Hex value and inserts appropriate bytes. 11 uNNNN Represents Unicode value and inserts UTF-8 sequence. Bytes to String Conversion Bytes can be converted to String using string() constructor. bytes memory bstr = new bytes(10); string message = string(bstr); Example Try the following code to understand how the string works in Solidity. pragma solidity ^0.5.0; contract SolidityTest { constructor() public{ } function getResult() public view returns(string memory){ uint a = 1; uint b = 2; uint result = a + b; return integerToString(result); } function integerToString(uint _i) internal pure returns (string memory) { if (_i == 0) { return “0”; } uint j = _i; uint len; while (j != 0) { len++; j /= 10; } bytes memory bstr = new bytes(len); uint k = len – 1; while (_i != 0) { bstr[k–] = byte(uint8(48 + _i % 10)); _i /= 10; } return string(bstr); } } Run the above program using steps provided in Solidity First Application chapter. Output 0: string: 3 Print Page Previous Next Advertisements ”;

Solidity – Environment Setup ”; Previous Next This chapter explains how we can setup Solidity compiler on CentOS machine. If you do not have a Linux machine then you can use our Online Compiler for small contracts and for quickly learning Solidity. Method 1 – npm / Node.js This is the fastest way to install Solidity compiler on your CentoS Machine. We have following steps to install Solidity Compiler − Install Node.js First make sure you have node.js available on your CentOS machine. If it is not available then install it using the following commands − # First install epel-release $sudo yum install epel-release # Now install nodejs $sudo yum install nodejs # Next install npm (Nodejs Package Manager ) $sudo yum install npm # Finally verify installation $npm –version If everything has been installed then you will see an output something like this − 3.10.10 Install solc Once you have Node.js package manager installed then you can proceed to install Solidity compiler as below − $sudonpm install -g solc The above command will install solcjs program and will make it available globally through out the system. Now you can test your Solidity compiler by issuing following command − $solcjs-version If everything goes fine, then this will print something as follows − 0.5.2+commit.1df8f40c.Emscripten.clang Now you are ready to use solcjs which has fewer features than the standard Solidity compiler but it will give you a good starting point. Method 2 – Docker Image You can pull a Docker image and start using it to start with Solidity programming. Following are the simple steps. Following is the command to pull a Solidity Docker Image. $docker pull ethereum/solc:stable Once a docker image is downloaded we can verify it using the following command. $docker run ethereum/solc:stable-version This will print something as follows − $ docker run ethereum/solc:stable -version solc, the solidity compiler commandlineinterfaceVersion: 0.5.2+commit.1df8f40c.Linux.g++ Method 3: Binary Packages Installation If you are willing to install full fledged compiler on your Linux machine, then please check official website Installing the Solidity Compiler. Print Page Previous Next Advertisements ”;