What is the memory keyword in Solidity?

In Solidity, we use the memory keyword to store the data temporarily during the execution of a smart contract.

When a variable is declared using the memory keyword, it is stored in the memory area of the EVMEthereum Virtual Machine. This is the default storage location for variables in Solidity. Moreover, it is used to store function arguments and return values.

It is easy to access memory and there is low cost involved. However, it is also volatile and has a limited capacity. That means the data stored in memory is not persistent and will be lost when the contract execution is finished. If we want data to persist, we will use the storage keyword.

How to use memory and storage

Output

The memory_working function returns array numbers=[1, 2, 3, 4, 5].

The storage_working function returns array numbers=[0, 2, 3, 4, 5].

Explanation

• Line 4: We create a contract HelloWorld.

• Line 6: We allocate a uint array numbers.

• Line 9: In memory_working function, we create a uint array A using the memory keyword and allocated it to the numbers array.

• Line 15: In storage_working function, we create a uint array B using the storage keyword. This will point B to the original array and any changes in B will change the array numbers.

After the execution of the contract the array A, which was allocated using memory keyword will be wiped out, but the array B will stay and can be accessed by future contracts.