MQL4 ERR_OBJECT_ALREADY_EXISTS
error 4200 MQL4 object already exists maps to ERR_OBJECT_ALREADY_EXISTS: object already exists. ObjectCreate was asked to create a chart object whose name already exists in the target chart. Capture GetLastError immediately after the failed call, correct the cause, and retry only when the condition can change.
Open the Coding Agent, then choose MQL4 from the language menu.
#property strict
void OnStart()
{
string object_name = "pineify_diagnostic_line";
if(ObjectFind(0, object_name) >= 0)
{
Print("Object already exists: ", object_name);
return;
}
ResetLastError();
if(!ObjectCreate(0, object_name, OBJ_HLINE, 0, 0, Bid))
{
Print("ObjectCreate failed. error=", GetLastError());
return;
}
ChartRedraw(0);
}The official MQL4 runtime table names error 4200 ERR_OBJECT_ALREADY_EXISTS and defines it as “object already exists.” ObjectCreate was asked to create a chart object whose name already exists in the target chart.
The error number is evidence about one failed call, not a diagnosis of the whole EA. Read the API sentinel first, then call GetLastError immediately because that function returns the current _LastError value and resets it.
Start with the inputs and external state that existed at the failure point. A later log entry or a successful call can overwrite the useful context.
Do not call ObjectCreate again with the same name. Update, delete, or rename the existing object first.
Keep the original trading and risk rules intact. A workaround that widens stops, increases volume, changes an account setting, or ignores a failed return value can hide the symptom while changing the system.
| Check | Action |
|---|---|
| OnInit or OnCalculate recreates the same object name | Check for the object before creating it. |
| Multiple indicator instances share a fixed object name | Include chart, symbol, timeframe, or instance identity in the name. |
| Old objects remain after removal or template changes | Update an existing object when reuse is intended. |
| The code does not check ObjectFind before ObjectCreate | Delete only objects owned by the program during cleanup. |
The script checks ObjectFind before creating the horizontal line and redraws the chart only after success.
The example improves validation and logging. It does not prove the operation will be accepted by a broker or behave safely in live trading.
#property strict
void OnStart()
{
string object_name = "pineify_diagnostic_line";
if(ObjectFind(0, object_name) >= 0)
{
Print("Object already exists: ", object_name);
return;
}
ResetLastError();
if(!ObjectCreate(0, object_name, OBJ_HLINE, 0, 0, Bid))
{
Print("ObjectCreate failed. error=", GetLastError());
return;
}
ChartRedraw(0);
}Pineify can generate or revise one self-contained .mq4 file with MQL4-specific reference context. Its independent static checker returns MetaEditor diagnostics so you can repair source issues before testing in your own MT4 environment.
Open MQL4 Coding AgentStatic diagnostics do not prove runtime behavior, backtest results, broker compatibility, or live-trading safety.
Check the API return value before interpreting an error number from the log.
Call GetLastError immediately and record error 4200, symbol, prices, volume, ticket, and terminal state relevant to the operation.
Check for the object before creating it.
Compile the revised source, then test with the same MT4 build, broker, symbol, account permissions, and market state.
ERR_OBJECT_ALREADY_EXISTS means object already exists. The code should still identify which API returned failure and log the inputs used for that call.
OnInit or OnCalculate recreates the same object name Multiple indicator instances share a fixed object name Old objects remain after removal or template changes The code does not check ObjectFind before ObjectCreate
Do not call ObjectCreate again with the same name. Update, delete, or rename the existing object first.
It reports the current _LastError value and resets it. Other operations can change the error state, so a delayed read may describe the wrong call.
Pineify can revise a self-contained .mq4 file, add validation and error logging, and return static MetaEditor diagnostics. It cannot prove broker acceptance, account permissions, market availability, or live execution.
Last verified against the linked official references on . Compile and test the final source in the MetaTrader 4 build, broker, symbol, and account environment you plan to use.
Define the requirement, inspect the generated source, repair diagnostics, and test the behavior in your own MT4 environment.
Open Coding Agent