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How to Concatenate the Strings in Solidity?

How to Concatenate the Strings in Solidity

Overview

Concatenating the strings means combining two strings to make one string. In Solidity, concatenating a string is a complex step. Like in some programming languages, we have a straightforward method: simply use the “+” sign and concatenate a string. But in Solidity, we can’t do this.

In Solidity, we have different built-in functions that offer string concatenation. In this article, we will discuss two functions one by one. So, let’s dive in.

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#1: Using the abi.encodePacked() function

In Solidity, some built-in functions can be called without importing any other contract. These functions are ABI-encoded functions. To concatenate the strings we can use abi.encodePacked() function. This function simply takes two strings and returns a single-byte type array which we convert to string to create one concatenated string.

Let’s look at an example.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract ExampleContract {

    function concatenate(string memory str1, string memory str2) public pure returns (string memory)
    {
				// Concatenating the strings
        return string(abi.encodePacked(str1, str2));
    }
}

Explanation

Let’s look at what we did in the example code.

  • We created a contract named ExampleContract.
  • We created a pure public function named concatenate that takes two memory-type string arguments and returns a memory-type string.
  • We return a string inside the function by concatenating the strings using the abi.encodePacked() function and then type-casting it to the string using the string() function.

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Output

Let’s look at how the output will look after running the code in the RemixIDE.

#2: Using the string.concat() function

Same as abi.encodePacked() function, Solidity’s newer versions offer a built-in function called string.concat() that you can use to perform string concatenation without importing any other contract. The string.concat() function takes two string arguments and returns one concatenated string.

Let’s look at an example.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract ExampleContract {

    function concatenate(string memory str1, string memory str2) public pure returns (string memory)
    {
				// Concatenating the strings 
        return string.concat(str1, str2);
    }
}

Explanation

Let’s look at what we did in the example code.

  • We created a contract named ExampleContract.
  • We created a pure public function named concatenate that takes two memory-type string arguments and returns a memory-type string.
  • Inside the function, we return a string by concatenating the two strings using the string.concat() function.

Output

Let’s look at how the output will look after running the code in the RemixIDE.

Conclusion

Concatenating the strings has become a straightforward process now as Solidity has evolved using the newer versions. There is also an iterative approach to concatenate the strings, but it is long and a bit tricky to implement. So, it is better to use the built-in functions and make your life easy peasy lemon squeezy.

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