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There are 3 contracts; A, B, and C. C has a state variable that with a default value. A changes that state variable to Yerevan. After that, B sees that variable. Evaluating by A is successful but B sees the default value again. It appears that B cannot call a updated smart contract. How can i change a state variable by an other smart contract constantly? is there any related work? please guide a beginner man. Thank you.

C:

pragma solidity ^0.5.12;

contract C{
   bytes public name;
   function rep(bytes memory pseudonym)  public returns(string memory){
       name=pseudonym;
       return string(name);
   }
   }

A:

pragma solidity ^0.5.12;
import "./C.sol";
contract A{
   bytes public fname="Yerevan";
   function naming() public returns(string memory){
      return C(0x8fcECc5B8d42EcF099E1cF032B1F505fbDA230A3).rep(fname);
  }
  }

B:

pragma solidity ^0.5.12;
import "./C.sol";
contract B{
   function rep() public returns(string memory){
      return string(C(0x8fcECc5B8d42EcF099E1cF032B1F505fbDA230A3).name());
   }
   }
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  • So what exactly is C c=new C() used for in here??? – goodvibration Feb 14 '20 at 19:04
  • It has to be deleted. Sorry for that. – Alireza Feb 14 '20 at 19:04
  • It was deleted. – Alireza Feb 14 '20 at 19:05
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There are some cases maybe you didn't pay attention:

  1. You are executing naming() from A by .call() not by .sendTransaction(). Obviously, it never mutates the state. I did guess that because of truffle-contract that there is in the tags list of your question.
  2. Maybe, you made a mistake in inserting the real address of C when you call it in both A and B. I mean here: C(0x8fcECc5B8d42EcF099E1cF032B1F505fbDA230A3).rep(...). That can be address of another deployed C.
  3. The same case @Rob Hitchens answered.
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Not enough is known about your tool stack and testing methodology to be sure. The comment about new C() suggests a situation that might have been enough to create unexpected results.

Intuitively, it may be about waiting for confirmation. It is almost a rite of passage to get confused about ti.

  • A is mutating the state, and that means nothing really happens until the transaction is mined. Mining/confirmation might take some time.

  • B is inspecting the state, and the Ethereum node will inspect its local copy of the blockchain without waiting. In particular, without waiting for A to update. It's entirely possible you might think A failed to do its job because you peeked too soon.

The asynchronous nature of this platform takes some getting used to.

Have a look at this explainer to see if any insights or oversights jump out. https://blog.b9lab.com/calls-vs-transactions-in-ethereum-smart-contracts-62d6b17d0bc2

Hope it helps.

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