I am new to Solidity. I am facing an issue in a simple operation of storing and retrieving data from mapping (uint=> address).

I have defined a simple contract:

contract test {
    mapping (uint => address) public testmap;

    function add_to_map  (uint _key, address _val) public{
        testmap[_key] = _val;
    function get_from_map(uint _key) returns (address){
        return testmap[_key];

In html, I am trying to do:

function createTestContract(){
    var test = testContract.at("0xc383dfb5fc71ff1bb2bbadb812229681fb7a8e3c");
    test.add_to_map(1, "0x12ca4a043753cd5537af99ad314a299962238ed2");       
    console.log('Key: 1'  + ' address: ' + test.get_from_map(1));

As output I am expecting address - 0x12ca4a043753cd5537af99ad314a299962238ed2 which I am stored against key 1. However, it is returning some random address in the console log.

Key: 1 address: 0x07824f2f2a330dd2e260437af299800175dc2642a63c71a5f824cee54eae2264

I am using private chain on AlethZero. Appreciate if anyone can help.

1 Answer 1


You need to specify constant so that you get the return value of a call:

function get_from_map(uint _key) constant returns (address).

Without constant, test.get_from_map(1) is a sendTransaction which always returns a transaction hash. See What is the difference between a transaction and a call?

  • Thank you @eth. It is clear now and it worked. Many thanks.
    – jrocky
    May 21, 2016 at 10:05

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