MQL4 ERR_INVALID_ARRAY
MQL4 error 4029 invalid array maps to ERR_INVALID_ARRAY: invalid array. An array argument, allocation, dimension, or operation does not satisfy the called array function. 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()
{
double values[];
int requested = 10;
int size = ArrayResize(values, requested);
if(size != requested)
{
Print("ArrayResize failed. error=", GetLastError());
return;
}
for(int i = 0; i < ArraySize(values); i++)
values[i] = i * 1.0;
Print("Last value: ", values[ArraySize(values) - 1]);
}The official MQL4 runtime table names error 4029 ERR_INVALID_ARRAY and defines it as “invalid array.” An array argument, allocation, dimension, or operation does not satisfy the called array function.
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.
Correct the allocation or array argument before repeating the operation. Retrying the same invalid array is not useful.
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 |
|---|---|
| A dynamic array was not resized before writing elements | Allocate the required logical size before writing. |
| An array function receives an unsupported dimension or array kind | Match the array function to the array type and supported dimension. |
| The code assumes ArrayResize succeeded without checking its result | Check the return value from ArrayResize and copy operations. |
| Array direction or logical size changes while cached indexes remain in use | Recalculate bounds after resize, copy, or ArraySetAsSeries changes. |
The script checks the allocated size, uses a strict less-than loop bound, and derives the final index from the current logical size.
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()
{
double values[];
int requested = 10;
int size = ArrayResize(values, requested);
if(size != requested)
{
Print("ArrayResize failed. error=", GetLastError());
return;
}
for(int i = 0; i < ArraySize(values); i++)
values[i] = i * 1.0;
Print("Last value: ", values[ArraySize(values) - 1]);
}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 4029, symbol, prices, volume, ticket, and terminal state relevant to the operation.
Allocate the required logical size before writing.
Compile the revised source, then test with the same MT4 build, broker, symbol, account permissions, and market state.
ERR_INVALID_ARRAY means invalid array. The code should still identify which API returned failure and log the inputs used for that call.
A dynamic array was not resized before writing elements An array function receives an unsupported dimension or array kind The code assumes ArrayResize succeeded without checking its result Array direction or logical size changes while cached indexes remain in use
Correct the allocation or array argument before repeating the operation. Retrying the same invalid array is not useful.
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