Error handling

As I mentioned many times in the previous articles if a function returns an error the code of this error you can get with the help of the GetLastError() function:

   int GetLastError()

After this function is called the last error code is set to zero, that’s why if a new error doesn’t emerge between two calls of the GetLastError() function for the second time it will return 0.

The GetLastError() function returns the numerical code of an error. If You want to get a text messages of errors you should use the ErrorDescription() function, defined in the stdlib.mqh file:

   string ErrorDescription(int error_code)
     {
      string error_string;
   //----
      switch(error_code)
        {
         //---- codes returned from trade server
         case 0:
           case 1:   error_string="no error";            break;
           case 2:   error_string="common error";   break;
            ...
        }
   //----
      return(error_string);
     }

The error codes returned from the trade server:

Constant	Value	Description
ERR_NO_ERROR	0	No error returned
ERR_NO_RESULT	1	No error returned, but the result is unknown
ERR_COMMON_ERROR	2	Common error
ERR_INVALID_TRADE_PARAMETERS	3	Invalid parameters
ERR_SERVER_BUSY	4	The trading server is busy
ERR_OLD_VERSION	5	The old version of the client terminal
ERR_NO_CONNECTION	6	No connection with the trading server
ERR_NOT_ENOUGH_RIGHTS	7	Not enough rights
ERR_TOO_FREQUENT_REQUESTS	8	Too frequent requests
ERR_MALFUNCTIONAL_TRADE	9	Malfunctional trade operation
ERR_ACCOUNT_DISABLED	64	Account disabled
ERR_INVALID_ACCOUNT	65	Invalid account
ERR_TRADE_TIMEOUT	128	Trade timeout
ERR_INVALID_PRICE	129	Invalid price
ERR_INVALID_STOPS	130	Invalid stops
ERR_INVALID_TRADE_VOLUME	131	Invalid trade volume
ERR_MARKET_CLOSED	132	Market is closed
ERR_TRADE_DISABLED	133	Trade is disabled
ERR_NOT_ENOUGH_MONEY	134	Not enough money for performing an operation
ERR_PRICE_CHANGED	135	Price changed
ERR_OFF_QUOTES	136	Off quotes
ERR_BROKER_BUSY	137	Broker is busy
ERR_REQUOTE	138	Requote (new prices)
ERR_ORDER_LOCKED	139	Order is locked and is being processed
ERR_LONG_POSITIONS_ONLY_ALLOWED	140	Long positions only are allowed
ERR_TOO_MANY_REQUESTS	141	Too many requests
ERR_TRADE_MODIFY_DENIED	145	Modification denied because order is too close to market
ERR_TRADE_CONTEXT_BUSY	146	Trade context is busy
ERR_TRADE_EXPIRATION_DENIED	147	To use expiration date of an order is prohibited by broker
ERR_TRADE_TOO_MANY_ORDERS	148	The number of open and pending orders has reached the limit set by broker

MQL4 run time error codes:

Constant	Value	Description
ERR_NO_MQLERROR	4000	No error
ERR_WRONG_FUNCTION_POINTER	4001	Wrong function pointer
ERR_ARRAY_INDEX_OUT_OF_RANGE	4002	Array index is out of range
ERR_NO_MEMORY_FOR_FUNCTION_CALL_STACK	4003	No memory for function call stack
ERR_RECURSIVE_STACK_OVERFLOW	4004	Recursive stack overflow
ERR_NOT_ENOUGH_STACK_FOR_PARAMETER	4005	Not enough stack for parameter
ERR_NO_MEMORY_FOR_PARAMETER_STRING	4006	No memory for parameter string
ERR_NO_MEMORY_FOR_TEMP_STRING	4007	No memory for temporary string
ERR_NOT_INITIALIZED_STRING	4008	Not initialized string
ERR_NOT_INITIALIZED_ARRAYSTRING	4009	Not initialized string in array
ERR_NO_MEMORY_FOR_ARRAYSTRING	4010	No memory for array string
ERR_TOO_LONG_STRING	4011	Too long string
ERR_REMAINDER_FROM_ZERO_DIVIDE	4012	Remainder from zero divide
ERR_ZERO_DIVIDE	4013	Zero divide
ERR_UNKNOWN_COMMAND	4014	Unknown command
ERR_WRONG_JUMP	4015	Wrong jump
ERR_NOT_INITIALIZED_ARRAY	4016	Not initialized array
ERR_DLL_CALLS_NOT_ALLOWED	4017	DLL calls are not allowed
ERR_CANNOT_LOAD_LIBRARY	4018	Cannot load library
ERR_CANNOT_CALL_FUNCTION	4019	Cannot call function
ERR_EXTERNAL_EXPERT_CALLS_NOT_ALLOWED	4020	External expert function calls are not allowed
ERR_NOT_ENOUGH_MEMORY_FOR_RETURNED_STRING	4021	Not enough memory for temp string returned from function
ERR_SYSTEM_BUSY	4022	System is busy
ERR_INVALID_FUNCTION_PARAMETERS_COUNT	4050	Invalid function parameters count
ERR_INVALID_FUNCTION_PARAMETER_VALUE	4051	Invalid function parameter value
ERR_STRING_FUNCTION_INTERNAL_ERROR	4052	String function internal error
ERR_SOME_ARRAY_ERROR	4053	Some array error
ERR_INCORRECT_SERIES_ARRAY_USING	4054	Incorrect series array using
ERR_CUSTOM_INDICATOR_ERROR	4055	Custom indicator error
ERR_INCOMPATIBLE_ARRAYS	4056	Arrays are incompatible
ERR_GLOBAL_VARIABLES_PROCESSING_ERROR	4057	Global variables processing error
ERR_GLOBAL_VARIABLE_NOT_FOUND	4058	Global variable not found
ERR_FUNCTION_NOT_ALLOWED_IN_TESTING_MODE	4059	Function is not allowed in testing mode
ERR_FUNCTION_NOT_CONFIRMED	4060	Function is not confirmed
ERR_SEND_MAIL_ERROR	4061	Send mail error
ERR_STRING_PARAMETER_EXPECTED	4062	String parameter expected
ERR_INTEGER_PARAMETER_EXPECTED	4063	Integer parameter expected
ERR_DOUBLE_PARAMETER_EXPECTED	4064	Double parameter expected
ERR_ARRAY_AS_PARAMETER_EXPECTED	4065	Array as parameter expected
ERR_HISTORY_WILL_UPDATED	4066	Requested history data in updating state
ERR_TRADE_ERROR	4067	Trade error
ERR_END_OF_FILE	4099	End of file
ERR_SOME_FILE_ERROR	4100	Some file error
ERR_WRONG_FILE_NAME	4101	Wrong file name
ERR_TOO_MANY_OPENED_FILES	4102	Too many opened files
ERR_CANNOT_OPEN_FILE	4103	Cannot open a file
ERR_INCOMPATIBLE_ACCESS_TO_FILE	4104	Incompatible access to a file
ERR_NO_ORDER_SELECTED	4105	No order selected
ERR_UNKNOWN_SYMBOL	4106	Unknown symbol
ERR_INVALID_PRICE_PARAM	4107	Invalid price parameter for trading function
ERR_INVALID_TICKET	4108	Invalid ticket
ERR_TRADE_NOT_ALLOWED	4109	Trade is not allowed
ERR_LONGS_NOT_ALLOWED	4110	Longs are not allowed
ERR_SHORTS_NOT_ALLOWED	4111	Shorts are not allowed
ERR_OBJECT_ALREADY_EXISTS	4200	Object exists already
ERR_UNKNOWN_OBJECT_PROPERTY	4201	Unknown object property is requested
ERR_OBJECT_DOES_NOT_EXIST	4202	Object does not exist
ERR_UNKNOWN_OBJECT_TYPE	4203	Unknown object type
ERR_NO_OBJECT_NAME	4204	No object name
ERR_OBJECT_COORDINATES_ERROR	4205	Object coordinates error
ERR_NO_SPECIFIED_SUBWINDOW	4206	No specified subwindow
ERR_SOME_OBJECT_ERROR	4207	Some object error

Next article: "Secrets of proper trade"