Consider the following contract in Solidity:

pragma solidity ^0.4.2;

contract Registry {
    struct Name {
        string first;
        string last;

    mapping(address => Name) reg;

    function newName(string first, string last) {
        address sender = msg.sender;

        if(reg[sender] != 0) {

        reg[sender].first = first;
        reg[sender].last = last;

In the if statement above, which is incorrect, I would like to check whether the struct Name is defined, or is still in the default value with all fields initialized to zero. Is there a language operator to do it?

3 Answers 3


I would go with:

if (reg[sender].first != "" || reg[sender].last != "") {

There's no operator but you can check the length of both strings against zero:

if (bytes(reg[sender].first).length != 0 || bytes(reg[sender].last).length != 0) { throw; }

Note: use of ||



To update this Answer to the latest version of Solidity. try the following: require(reg[sender].first && reg[sender].last);

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