MQL4 error diagnosis
For an MQL4 exit with error, record the failure where it occurs, return from the current handler, and let OnDeinit release resources when the terminal actually unloads or reinitializes the program. OnDeinit receives a reason code, but it is not a general exception handler and should not start new trades.
Open the Coding Agent, then choose MQL4 from the language menu.
#property strict
int OnInit()
{
Print("EA initialized.");
return(INIT_SUCCEEDED);
}
void OnDeinit(const int reason)
{
Print("EA deinitialized. reason=", reason,
" last_error=", GetLastError());
// Release files, timers, objects, and other owned resources here.
// Do not start a new trade while the program is being removed.
}
void OnTick()
{
if(Bars < 2)
return;
}Returning from OnTick, OnTimer, or a helper stops the current path only. The EA remains attached and can receive later events. Use a disabled state flag when a critical failure should block future work without removing the program.
Initialization can return INIT_FAILED when required inputs or resources are unavailable. That communicates failure through the documented lifecycle.
The terminal calls OnDeinit before reinitialization or unloading and supplies a reason such as chart change, input change, account change, template application, removal, or terminal close.
Keep the original runtime error in its own log. The deinitialization reason describes lifecycle state and is not a replacement for the earlier GetLastError value.
Kill timers, close valid file handles, release resources, and delete only objects created under the program’s own prefix. Cleanup should be idempotent because partial initialization is possible.
The EA has documented OnInit, OnTick, and OnDeinit signatures. OnDeinit records its reason and is reserved for resource cleanup, not recovery trading.
Shutdown paths should not change account exposure unexpectedly. Test lifecycle events on a demo setup and keep position management outside OnDeinit.
#property strict
int OnInit()
{
Print("EA initialized.");
return(INIT_SUCCEEDED);
}
void OnDeinit(const int reason)
{
Print("EA deinitialized. reason=", reason,
" last_error=", GetLastError());
// Release files, timers, objects, and other owned resources here.
// Do not start a new trade while the program is being removed.
}
void OnTick()
{
if(Bars < 2)
return;
}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.
Log the failed API, return, immediate error, and relevant state where it occurred.
Return or switch to a disabled state so later code cannot use invalid resources.
Use OnDeinit for timers, handles, objects, and other lifecycle cleanup.
Exercise removal, chart changes, input changes, failed initialization, and terminal shutdown.
Log the failure and return from the current handler. Use INIT_FAILED for an initialization failure or a disabled state for a critical runtime condition.
No. It ends only the current OnTick call. The EA can receive later events while it remains attached.
Not as a general exception handler. It is called for program uninitialization or reinitialization events defined by the terminal.
Do not start new trade work during shutdown. Any position-exit policy belongs in normal, testable trade-management logic with explicit risk rules.
Log the deinitialization reason and cleanup result separately from the original operation error.
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