Good day I've got a struct like this, and I also declare an array to store this struct.

Then in the same contract, I tried to check if the corresponding struct is null or not by checking its length equals to zero.

But the compiler shows me the error msg in if (propertyList[_id].length == 0) throw; of removeProperty function

Member "length" not found or not visible after argument-dependent lookup in struct Property storage ref

But if I create a function

function getPropertiesLength() constant returns(uint){
    return propertyList.length;

Then modify my code to if (getPropertiesLength() == 0) throw;

it works just fine. Why? 0.0

My code is listed below. I appreciate any suggestions and opinions :)

Many thanks!!!

contract usingProperty{
    struct Property{
        bytes32 name;
        uint id;
        mapping (address => bool) accessStakeholders;
        uint[] rating;

    Property[] public propertyList;

    function addProperty(bytes32 _name, address[] _accessStakeholders, uint _rating) returns(bool success, uint _id){

        _id = propertyList.length++;

        Property prop = propertyList[_id];
        for (uint i = 0 ; i < _accessStakeholders.length ; i++){
          prop.accessStakeholders[_accessStakeholders[i]] = true;

        prop.name = _name;
        prop.id= _id;

    function removeProperty(uint _id){
        if (propertyList[_id].length == 0) throw;


1 Answer 1


Ethereum Virtual Machine (EVM) cannot differ between non-inialized and zero data.

Check the struct for a zero value member that should not be zero. What you can do is:

  if (propertyList[_id].id == 0) throw; 

Of course, in this case, id zero must be a special reserved id in your decentralizd application logic.

  • it works ! But I'm wondering why it also works once I replace getPropertiesLength() function with propertyList[_id].length ?
    – johnhckuo
    Commented Feb 22, 2017 at 11:55
  • The reason is becase with propertyList[_id] you're possibly accessing a Property value in your propertyList mapping and the Property struct doesn't have a length member. getPropertiesLength() works because it executes length on the propertyList mapping itself, that has a length member. Commented Aug 12, 2017 at 22:10

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