Validating for non-zero Fields in Solidity for Contracts

Question

In the sample code below, I wanted to check the input data (non-empty) using require/assert and create the contract if it passes the two test.

The code is not working. It still creates an instance of a Contract ABC, if I provide just the _name value as input, without the _number.

How do you make the function "create" exit if the require conditions are not met. How would I tweak this code to achieve the above? Do I have to wrap the require condition with an if-then-else to return false if tests fail? Thanks.

pragma solidity ^0.4.15;
contract ABC {

    bytes32 public name;
    uint public number;
    event Log(string _myString);        

    function ABC (bytes32 _name, uint _number) public {
        Log("object created");
        name = _name;
        number = _number;

    }
}

contract XYZ {

    ABC myABC;

    event Log(string _myString);

    function create(bytes32 _name, uint _number) public returns (bool isSuccess) {

        Log("checking name");
        require(_name != 0);

        Log("name valid, now checking number");
        require(_number != 0);

        Log("name and number non-empty, creating a new contract");
        myABC = new ABC(_name,_number);

        Log("new contract created");

        return true;

    }


}

Answer 1

As far as I know, in Solidity there is no "null" equivalent. This means you need to get a bit clever with how you check for empty values.

bytes32 is really an array with a fixed length of 32. In order to check for an empty value here you can try the following:

require(_name[0] != 0);

This will check whether or not the string being passed in is empty.

As for the uint, I made the following change in the XYZ contract:

uint public number;
...
number = _number;

Since public variables in Solidity have "built-in" getter functions I was able to check its value (after deploying it on Remix). It appears that it is initialized as 0. This means that as long as you consider 0 to be a valid value to be passed into ABC you don't even need to check whether or not _number is non-zero.

Hope that helps!

Answer 2

I tried your code and it is working as expected. It is throwing error when not passing the _number argument to create method of contract XYZ.

You can try to compile the code on remix and check the same.