does it cost gas when executing view or pure function in solidity?

Question

Let's suppose i have the following code in ethereum's solidity function:

function getArray() external pure returns(uint[]) {
  // Instantiate a new array in memory with a length of 3
  uint[] memory values = new uint[](3);
  // Add some values to it
  values.push(1);
  values.push(2);
  values.push(3);
  // Return the array
  return values;
}

As it's pure, it doesn't even read data from storage, doesn't change anything in storage. So imagine I deployed this contract. then there're people who want to invoke this function from web3.js or remix for example. Will this function cost them gas? I've read that view functions and pure functions are the way that don't change the storage. so they're free (no gas). If users use above function, why is it free? i still make the calculation and save temprorary data to memory.

Answer 1

It depends,

If they call a pure function itself, like the one in your example, getArray(), then no, it won't cost anything.

However, if they call a function which isn't pure or view, and that function internally calls the getArray() function, then they will have to pay for the whole transaction.

Answer 2

Nothing is free. Processing instructions cost gas, just much much less than a transaction that changes state. It may not cost gas when the EVM is run in popular IDEs, which can lead to the false belief that pure functions cost nothing.

This basic function:

    function bigLoop(uint max) public pure returns (uint) {
      uint n;
      for(n = 0; n < max; n++) {
      }
      return n;
    }

called from a web3 client with max = 310000 hitting a local dev geth node (geth --dev) will throw an out of gas exception. If you throw this into the loop:

    function bigLoop(uint max) public pure returns (uint) {
      uint n;
      for(n = 0; n < max; n++) {
         bytes memory dummy = new bytes(256);
      }
      return n;
    }

then max = 11000 will throw out of gas.