How are returns objects converted in geth?

Question

I have a function which returns an uint, but actually gets an object - how is that converted.

e.g.

f

   "0x91f35a1267f2c8d763f7a3fb35ffac845fcbb1417a64b030ed79cbaa4e29694f"

f is defined as the return to the following function:

function testReturn() returns (uint) {
    studentAge=90;
    return 89;
 }

There must be a way to convert the return from this function.

The contract is defined as:

contract CollegeAdmin {
    uint8 public studentAge=21;
    uint16 public studentIncome=15000;
    uint8 public studentScore=4;

    uint8 public studentAttendance=96;

    function testReturn() returns (uint) {
        studentAge=90;
        return 89;
    }
}

Hence f is defined using:

f = con.testReturn()

Also, con is defined:

con = eth.contract(abi).at(addr)

abi - abi for contract addr - contract address

score 1 · Answer 1 · answered Feb 26 '18 at 11:07

1

I tested by adding constant and that worked. I am unsure what it returned before, but with constant added it worked -

   function testReturn() constant returns (uint) {
       studentAge=90;
       return 89;
   }

answered Feb 26 '18 at 11:07

Trevor Lee Oakley

2,327
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Constants methods can not modify state. SO the studentAge will not be updated to 90. – Prashant Prabhakar Singh Feb 26 '18 at 11:10
That is useful to know about the state variable. I am only testing what functions can do. Constant is needed to return the integer apparently. – Trevor Lee Oakley Feb 26 '18 at 11:18
Yes. In case you have to modify state as well as return values. You have to Solidity events. :) – Prashant Prabhakar Singh Feb 26 '18 at 11:23
The issue is all about constant. It seems that is needed to do a call otherwise sendTransaction applies. – Trevor Lee Oakley Feb 26 '18 at 12:03

Prashant Prabhakar Singh · Answer 2 · 2018-02-26T10:37:29.523

0

Non-contract functions can not return values. Use Events instead.

Or mark your function constant (or view) (if the function doesn't modify the state).

function testReturn() constant returns (uint) {
    studentAge=90;
    return 89;
 }

The following statements are considered modifying the state:

Writing to state variables.
Emitting events.
Creating other contracts.
Using selfdestruct.
Sending Ether via calls.
Calling any function not marked view or pure.
Using low-level calls.
Using inline assembly that contains certain opcodes.

If you are not reading any state variables better make function pure.

function testReturn() pure returns (uint) {
        return 89;
     }

Read more about view functions and pure functions.

edited Feb 26 '18 at 10:37

answered Feb 26 '18 at 10:33

Prashant Prabhakar Singh

8,026
5
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The func is coded in a smart contract, and deployed into the ethereum blockchain and then referred via geth and the con object, the question I asked related to converting the returned object into a number. It is not related to view and pure, or events. – Trevor Lee Oakley Feb 26 '18 at 10:36
The smart-contract function can not return a value if this is not constant. It only returns transaction hash. The return type can use while while making calls from some other function. – Prashant Prabhakar Singh Feb 26 '18 at 10:39
Better if you post the code you are using along with the object you are getting. – Prashant Prabhakar Singh Feb 26 '18 at 10:40
I am only asking how to convert objects in geth. – Trevor Lee Oakley Feb 26 '18 at 10:41
What object did you want to convert? You are calling a non-constant function and this will not return you 89 (as you may be expecting). You need to use Events. See: returning value from non-constant functions – Prashant Prabhakar Singh Feb 26 '18 at 10:44
My issue is not related to events in anyway. I am only asking how to see a number using the geth console returned from a function. If my func did not return 89 what did it return? – Trevor Lee Oakley Feb 26 '18 at 10:57
It will return the transaction hash. You call a non-constant function that is changing state variable (studentAge). So this transaction is broadcasted to the network and when this tx is mined, the value of state variable will be updated. – Prashant Prabhakar Singh Feb 26 '18 at 11:09

How are returns objects converted in geth?

2 Answers2