States

The state refers to the persistent data of a contract — essentially the member variables defined within the contract struct. It holds the current values of the contract and must remain identical across all nodes in the Qubic network to maintain deterministic execution and consensus. Any modification to the state must be performed carefully through defined procedures.

The contract state is passed to the functions & procedures as a reference named state.

1. Example how to create a state number

The myNumber variable is called state of the MYTEST contract

struct MYTEST : public ContractBase
{
public:
  sint64 myNumber;
};

1. Example how to modify state number

struct MYTEST : public ContractBase
{
public:
  sint64 myNumber;

  struct changeNumber_input
  {
    sint64 myNumber;
  };

  struct changeNumber_output
  {
  };

  // Reminder: The contract state is passed to the functions & procedures
  // as a reference named `state`.
  PUBLIC_PROCEDURE(changeNumber)
  {
    // myNumber = input.myNumber; is wrong
    state.myNumber = input.myNumber;
  }

  // WRONG, function can't modify state
  // PUBLIC_FUNCTION(changeNumber)
  // {
  //   state.myNumber = input.myNumber;
  // }
};

warning

Attempting to modify the state inside a function will result in the error "expression must be a modifiable lvalue", because functions are not allowed to change contract state.

info

The memory available to the contract is allocated statically, but extending the state will be possible between epochs through special EXPAND events (this event is not implemented yet).