Version Pragma - Structure of an Ethereum Smart Contract

This pragma directive tells the compiler to use the correction version to compile the contract and to reject compiling with an incompatible compiler. This annotation ensures that our code is always compiled correctly as we intended.

The version pragma is used as follows:

pragma solidity ^0.4.14;

This directive is optional, but is highly recommended to annotate every source file with this version pragma. The version pragma uses semantic versioning and is denoted by [major, minor, patch] tuple. As shown above 0.4.14.

In the above version directive we used caret range to specify the supported compilers. The caret range allows compiler greater than the specified version and does not allow compiler greater than the left most non-zero digit. In our definition the left most non-zero digit is 4 (0.4). So the caret range allows compiler greater than the specified version (0.4.14) and does not allow greater than the left most non-zero digit (0.5.0). In other words, only compiler with version >= 0.4.14 and < 0.5.0 be allowed to compile to compile our contract code. This version pragma directive can also include prerelease tags such as alpha, beta. Below are examples of caret ranges:

•  ^0.4.14 := >=0.4.14 and <0.5.0
•  ^1.2.3 := >=1.2.3 and <2.0.0
•  ^0.2.3 := >=0.2.3 <0.3.0
•  ^0.0.3 := >=0.0.3 <0.0.4

The solidity compiler can use complex rules for identifying the correct compiler version. But this may be rarely used. Unless you want to target a specific version range, you don’t need to go that complex.

This blog is part of Structure of an Ethereum Smart Contract, please refer to it for more details.