A tiny problem about mapping in solidity (parse error when initializing the mapping)

Question

I encountered this problem when I designed a test contract and initialized the mapping therein as provided below.

pragma solidity ^0.4.10;

contract test{

    mapping (uint256 => string) uintTostring;

    uintTostring[uint256(1)]="1";
}

The compiler says there is parse error about this command " uintTostring[1]='1' " Where do I make wrong and how I can solve this problem?

Answer 1

You need to create a setter function to set the value of the mapping variable "uintTostring".

Below is a very basic and simple example for the same:

pragma solidity ^0.4.10;
contract test{
    mapping (uint256 => string) uintTostring;
    function setValueOfVariable() {
        uintTostring[1] = "1";
    }
}

You can also pass the parameters to this function to make it more flexible. Also to retrieve the variable a getter function would be required or declare the variable as public.

Hope this helps..!

Answer 2

try this code :

pragma solidity ^0.4.10;

contract test{

function bytes32ToString (bytes32 data) returns (string) {
    bytes memory bytesString = new bytes(32);
    for (uint j=0; j<32; j++) {
        byte char = byte(bytes32(uint(data) * 2 ** (8 * j)));
        if (char != 0) {
            bytesString[j] = char;
        }
    }
    return string(bytesString);
}
    mapping (uint256 => string) uintTostring;

   function f(uint i){
       uintTostring[i]=bytes32ToString(bytes32(i));
   } 
}

and read about conversion of uint to string : Conversion of uint to string