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MQL5 runtime error reference

MQL5 Error 4802: Indicator cannot be created

MQL5 error 4802 officially means "Indicator cannot be created." An iCustom or built-in indicator constructor returned INVALID_HANDLE because the indicator path, inputs, symbol, timeframe, or required resource was not valid in that context. Check the returned handle immediately, verify the exact indicator path and parameter order, compile the dependency, and ensure it is available to the terminal or Strategy Tester. Capture GetLastError immediately around the failing call so an older error is not mistaken for the current failure.

Open MQL5 Coding AgentReview the diagnostic example

Open the Coding Agent and choose MQL5 from the language menu.

Isolate runtime error 4802.mq5
int handle=INVALID_HANDLE;

int OnInit()
  {
   ResetLastError();
   handle=iCustom(_Symbol,_Period,"Examples\CustomIndicator",14);
   if(handle==INVALID_HANDLE)
     {
      PrintFormat("iCustom failed, error=%d",GetLastError());
      return INIT_FAILED;
     }
   return INIT_SUCCEEDED;
  }
  • Official meaning: Indicator cannot be created
  • Layer: terminal runtime
  • Read with: GetLastError
  • First step: isolate the failing call

Where error 4802 comes from

An iCustom or built-in indicator constructor returned INVALID_HANDLE because the indicator path, inputs, symbol, timeframe, or required resource was not valid in that context. The numeric value is listed in the official runtime error table, which is separate from MetaEditor compilation errors and trade server return codes.

Reset the last-error state before the suspected call, save its direct return value, and read GetLastError immediately afterward. This produces a causal log instead of a stale code.

Checks that narrow the cause

Preserve the exact parameters and terminal context that produced the failure. Check one precondition at a time before adding retries.

  • Test every created handle against INVALID_HANDLE.
  • For iCustom, verify the relative path and escaped folder separators.
  • Match the custom indicator input count, order, and types.
  • In Strategy Tester, make dynamic dependencies discoverable with #property tester_indicator when required.

Apply the smallest repair

Check the returned handle immediately, verify the exact indicator path and parameter order, compile the dependency, and ensure it is available to the terminal or Strategy Tester.

After the repair, test both the expected path and a deliberately invalid input. The second test confirms that the diagnostic branch still exposes failures.

Use a focused diagnostic

The initialization fails explicitly when the indicator handle cannot be created. Replace the path and input list with the exact compiled dependency contract.

A clean compile or a cleared error code does not prove strategy logic, broker compatibility, backtest quality, or live-trading safety. Reproduce the result in the target MetaTrader 5 terminal and account environment.

Isolate runtime error 4802.mq5
int handle=INVALID_HANDLE;

int OnInit()
  {
   ResetLastError();
   handle=iCustom(_Symbol,_Period,"Examples\CustomIndicator",14);
   if(handle==INVALID_HANDLE)
     {
      PrintFormat("iCustom failed, error=%d",GetLastError());
      return INIT_FAILED;
     }
   return INIT_SUCCEEDED;
  }
Where Pineify fits

Repair editable MQL5 source with compiler feedback

Pineify can generate or revise MQL5 source and use MQL5 compilation diagnostics during the coding workflow. Keep the exact error, source location, program type, and intended behavior in the request so the change remains reviewable.

Open MQL5 Coding Agent

Pineify does not run your broker terminal, Strategy Tester, market data, or live orders. Validate the final program in your own MetaTrader 5 environment.

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A practical verification workflow

  1. 1

    Reset the error state

    Call ResetLastError directly before the suspected function so the next code belongs to that operation.

  2. 2

    Record call and inputs

    Save the function return value, every input, and GetLastError. Confirm that the captured runtime code is 4802.

  3. 3

    Validate the preconditions

    Test every created handle against INVALID_HANDLE. For iCustom, verify the relative path and escaped folder separators. Match the custom indicator input count, order, and types. In Strategy Tester, make dynamic dependencies discoverable with #property tester_indicator when required.

  4. 4

    Retest in the target terminal

    Compile the changed source, repeat the failing operation, and test the surrounding EA or indicator behavior in MetaTrader 5.

Frequently asked questions

What does MQL5 error 4802 mean?

The official runtime error table defines 4802 as "Indicator cannot be created."

Is error 4802 a compiler error?

No in this context. It is a terminal runtime code. Compiler diagnostics and MqlTradeResult.retcode values use separate code tables.

Why should I call ResetLastError first?

The terminal stores the last runtime error. Resetting it before the suspected call makes the following GetLastError value easier to attribute to that call.

Last verified against the linked official references on . Compile and test the final source in the MetaTrader 5 build, broker, symbol, and account environment you plan to use.

Continue with reviewable MQL5 source

Provide the exact diagnostic and intended behavior, inspect the generated change, compile it, and verify it in your MT5 test environment.

Open MQL5 Coding Agent