Why struct are not stored in my smart contract

Question

I have written a code to add offer in my contract, however, when I compiled the code in the console and I tried to return the number of offer in this contract, I got 0. PS: I tried this code in the solidity compiler online and it works well !

pragma solidity ^0.4.9;

contract Offer {

    address public owner;
    struct Offer {
        string title;
        string description;
        uint  offerTime;
        mapping (address => uint) subscribers;
        mapping (uint => address) subscribersAddress;
        mapping (uint => uint) nbrSubscribersPerID;
        uint price;
    }

    Offer[] public  offers;


    // add offer
    function addOffer(string  description1, string title1, uint price1,uint offerTime1) 
      returns (uint, string, string, uint, uint) {
        uint offerID = offers.length++;
        Offer o = offres[offreID];

        o.description = description1;
        o.offerTime=offerTime1;
        o.title = title1;
        o.price = price1;
        return (offerID, offers[offerID].description, offers[offerID].title, offers[offerID].price, 
          offers[offerID].offerTime);
    }

    //return the  number of offers 
    function returnNbroffer() public returns(uint) {
        uint nbr_offer =offers.length;
        return(nbr_offer);
    }
}

---

I still getting 0 in my console! I replaced public with constant but it doesn't work! I dont know why it works well when I tested it in the solidity compiler online .

Answer 1

It is because your returnNbroffer() function was not marked constant. I have replaced public with constant and this code works:

pragma solidity ^0.4.9;

contract Offer {

    address public owner;
    struct Offer {
        string title;
        string description;
        uint  offerTime;
        mapping (address => uint) subscribers;
        mapping (uint => address) subscribersAddress;
        mapping (uint => uint) nbrSubscribersPerID;
        uint price;
    }

    Offer[] public  offers;


    // add offer
    function addOffer(string  description1, string title1, uint price1,uint offerTime1) 
      returns (uint, string, string, uint, uint) {
        uint offerID = offers.length++;
        Offer o = offers[offerID];

        o.description = description1;
        o.offerTime=offerTime1;
        o.title = title1;
        o.price = price1;
        return (offerID, offers[offerID].description, offers[offerID].title, offers[offerID].price, 
          offers[offerID].offerTime);
    }

    //return the  number of offers 
    function returnNbroffer() constant returns(uint) {
        uint nbr_offer =offers.length;
        return(nbr_offer);
    }
}

Here is the modified version of your code that I flattened, pasted and deployed from the geth console:

> var offerSource='pragma solidity ^0.4.9;contract Offer { address public owner; struct Offer { string title; string description; uint offerTime; mapping (address => uint) subscribers; mapping (uint => address) subscribersAddress; mapping (uint => uint) nbrSubscribersPerID; uint price; } Offer[] public offers;  function addOffer(string description1, string title1, uint price1,uint offerTime1)  returns (uint, string, string, uint, uint) { uint offerID = offers.length++; Offer o = offers[offerID]; o.description = description1; o.offerTime=offerTime1; o.title = title1; o.price = price1; return (offerID, offers[offerID].description, offers[offerID].title, offers[offerID].price,  offers[offerID].offerTime); }  function returnNbroffer() constant returns(uint) { uint nbr_offer =offers.length; return(nbr_offer); }}'
undefined
> var offerCompiled=web3.eth.compile.solidity(offerSource);
undefined
> var offerContract = web3.eth.contract(offerCompiled['<stdin>:Offer'].info.abiDefinition);
undefined
> var offer = offerContract.new({
    from: web3.eth.accounts[0],
    data: offerCompiled['<stdin>:Offer'].code, gas: 600000},
    function(e, contract) {
      if (!e) {
        if (!contract.address) {
          console.log("Contract transaction send: TransactionHash: " +
            contract.transactionHash + " waiting to be mined...");
        } else {
          console.log("Contract mined! Address: " + contract.address);
          console.log(contract);
        }
    }
});
Contract transaction send: TransactionHash: 0x68ee1322883fef739b82fea9c267d9941cfe19408a5c67b0f2d894d5c5d7fa39 waiting to be mined...
undefined
> Contract mined! Address: 0x31e137906cc44ff6e1a1a098303bd7573fe715cc

I checked the transaction receipt:

> eth.getTransactionReceipt("0x68ee1322883fef739b82fea9c267d9941cfe19408a5c67b0f2d894d5c5d7fa39")
{
  blockHash: "0xf3b2ba913e43ad8b7a1377ec3e066f6a1436605fbf2423a08bc189d04dae6557",
  blockNumber: 7932,
  contractAddress: "0x31e137906cc44ff6e1a1a098303bd7573fe715cc",
  cumulativeGasUsed: 577610,
  from: "0x000d1009bd8f0b1301cc5edc28ed1222a3ce671e",
  gasUsed: 577610,
  logs: [],
  logsBloom: "0x00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000",
  root: "0x4a336c0521b10b59bd335a2b1242ff9a79bb30be7f22e31c3d884a60c63030d7",
  to: null,
  transactionHash: "0x68ee1322883fef739b82fea9c267d9941cfe19408a5c67b0f2d894d5c5d7fa39",
  transactionIndex: 0
}

I sent an addOffer(...) transaction and waited for a short while:

> offer.addOffer("one", "one", 1, 1, {from: eth.accounts[0], gas: 400000});
"0x103f16250f3b5e71144bde66b61ddbe07a02b3dfc2ac670513dae77083cf525a"

I then checked the constant function:

> offer.returnNbroffer()
1

With the constant function modifier added, your contract seems to work as expected. Sometime you also have to increase the gas.

Answer 2

I found two issues in your code:

I. Typos

Offer o = offres[offreID];

should be

Offer o = offres[offerID];

II. There is a difference between a read and a write operation in the blockchain.

o Write means you send a transaction which will be mined. This operation cost gas and takes a few seconds.

To declare a write function in Solidity, just do what you wrote:

function functionName(args) returns (return_args) {
}

o Read doesn't cost any gas because your node contains the blockchain, no transaction are processed for that. To explicitly tag a function for read, use the keyword constant

function functionName(args) constant returns (return_args) {
    return a;
}

In your case

//return the  number of offers 
function returnNbroffer() constant returns(uint) {
    uint nbr_offer =offers.length;
    return(nbr_offer);
}

Documentation:

• Solidity Constant function

• Web3 (Javascript console) - Call a function

---

EDIT

truffle(development)> var c = web3.eth.contract(Offer.abi);
undefined
truffle(development)> Offer.address
'0x10fdfeecd15082519ab1b0648df07831c665d5d6'
truffle(development)> var i = c.at('0x10fdfeecd15082519ab1b0648df07831c665d5d6');
undefined
truffle(development)> i.addOffer("a", "b", 10, 5, {from: web3.eth.accounts[0]});
'0xbaaf59c7ce30a54a44a56553d58ecb2aa4e84b02e59508d97ad43419491733e7'
truffle(development)> i.returnNbroffer.call().toNumber()
1

Answer 3

May help you. I tested with Mist.

pragma solidity ^0.4.9;

contract OfferContract {

    address public owner;
    struct Offer {
        string title;
        string description;
        uint  offerTime;
        mapping (address => uint) subscribers;
        mapping (uint => address) subscribersAddress;
        mapping (uint => uint) nbrSubscribersPerID;
        uint price;
    }

    Offer[] public  offers;


    // add offer
    function addOffer(string  description1, string title1, uint price1,uint offerTime1) public
      returns (uint, string, string, uint, uint) {
        uint offerID = offers.length++;
        Offer storage o = offers[offerID];

        o.description = description1;
        o.offerTime=offerTime1;
        o.title = title1;
        o.price = price1;
        return (offerID, offers[offerID].description, offers[offerID].title, offers[offerID].price, 
          offers[offerID].offerTime);
    }

    //return the  number of offers 
    function returnNbroffer() constant public returns(uint) {
        uint nbr_offer =offers.length;
        return(nbr_offer);
    }
}