How to find out if an Ethereum address is a contract?

ethereum solidity smartcontracts
bortzmeyer picture bortzmeyer · Jun 5, 2016 · Viewed 15.4k times · Source

An address in Solidity can be an account or a contract (or other things, such as a transaction). When I have a variable x, holding an address, how can I test if it is a contract or not?

(Yes, I've read the chapter on types in the doc)

Answer

Manuel Araoz picture Manuel Araoz · Dec 2, 2016

Yes you can, by using some EVM assembly code to get the address' code size:

function isContract(address addr) returns (bool) {
  uint size;
  assembly { size := extcodesize(addr) }
  return size > 0;
}

Related questions

Are there null like thing in solidity

struct buyer{ uint amount; Status status; } mapping(address=>buyer) public buyers; mapping(uint=>address) buyerIndex; uint public buyerNum; //Order a product. function(){ uint doubleValue=value*2; uint amount=msg.value/doubleValue; if(buyers[msg.sender]==null){ //Error in this …

Read More
String concatenation in solidity?

how do i concatenate strings in solidity? var str = 'asdf' var b = str + 'sdf' seems not to work.. I looked up the documentation (https://github.com/ethereum/wiki/wiki/Solidity-Tutorial#elementary-types-value-types) and there is not much mentioned about string concatenation. …

Read More
String array in solidity

I came across quite a common problem that it seems I can't solve elegantly and efficiently in solidity. I've to pass an arbitrary long array of arbitrary long strings to a solidity contract. In my mind it should be something …

Read More