MQL4 to MQL5 compatibility library - MetaTrader 5용 라이브러리

Put mql4compat.mqh in your Include directory (it resides on your Windows user roaming profile).

In your MQL4 EA/indicator/library/script please add right after #property definitions:

#include <mql4compat.mqh>

Change MQL4 functions:

int init() to int OnInit()
int deinit() to void OnDeinit(const int reason);
int start() in script to void OnStart();
int start() in  indicator to:
int OnCalculate(const int rates_total,
                const int prev_calculated,
                const datetime &time[],
                const double &open[],
                const double &high[],
                const double &low[],
                const double &close[],
                const long &tick_volume[],
                const long &volume[],
                const int &spread[])
  {

The last line with return() function then should be as following:

   return(rates_total);

 Change conflicting functions between MQL4 and MQL5 due their changed parmeters by adding MQL4 to their names:

   int ArrayInitializeMQL4(double &array[], double value)
   int ArrayMaximumMQL4(double &array[], int count=WHOLE_ARRAY, int start=0)
   int ArrayMinimumMQL4(double &array[], int count=WHOLE_ARRAY, int start=0)
   int ArraySortMQL4(double &array[], int count=WHOLE_ARRAY, int start=0, int sort_dir=MODE_ASCEND)
   double CopyBufferMQL4(int handle,int index,int shift)
   double EnvelopesMQL4(string symbol, int tf, int ma_period, int method, int ma_shift, int price, double deviation, int mode, int shift)
   double FileReadDoubleMQL4(int handle, int size=DOUBLE_VALUE)
   bool FileSeekMQL4(long handle, int offset, ENUM_FILE_POSITION origin)
   int IndicatorCountedMQL4(int _prev_calculated=0)
   bool ObjectCreateMQL4(string name, ENUM_OBJECT type, int window, datetime time1, double price1, datetime time2=0, double price2=0, datetime time3=0, double price3=0)
   bool ObjectDeleteMQL4(string name)
   string ObjectDescriptionMQL4(string name)
   int ObjectFindMQL4(string name)
   bool ObjectMoveMQL4(string name, int point, datetime time1, double price1)
   string ObjectNameMQL4(int index)
   int ObjectsDeleteAllMQL4(int window=EMPTY, int type=EMPTY)
   int ObjectsTotalMQL4(int type=EMPTY, int window=-1)
   bool SetIndexBufferMQL4(int index, double &array[])
   string StringConcatenateMQL4(string _str1,string _str2, ... string _str64="")
   int StringGetCharMQL4(string text, int pos)
   string StringSetCharMQL4(string text, int pos, int value)
   double iACMQL4(string symbol, int tf, int shift)
   double iADMQL4(string symbol, int tf, int shift)
   double iADXMQL4(string symbol, int tf, int period, int price, int mode, int shift)
   double iAOMQL4(string symbol, int tf, int shift)
   double iATRMQL4(string symbol, int tf, int period, int shift)
   double iAlligatorMQL4(string symbol, int tf, int jaw_period, int jaw_shift, int teeth_period, int teeth_shift, int lips_period, int lips_shift, int method, int price, int mode, int shift)
   double iBWMFIMQL4(string symbol, int tf, int shift)
   double iBandsMQL4(string symbol, int tf, int period, double deviation, int bands_shift, int method, int mode, int shift)
   double iBearsPowerMQL4(string symbol, int tf, int period, int price, int shift)
   double iBullsPowerMQL4(string symbol, int tf, int period, int price, int shift)
   double iCCIMQL4(string symbol, int tf, int period, int price, int shift)
   double iDeMarkerMQL4(string symbol, int tf, int period, int shift)
   double iForceMQL4(string symbol, int tf, int period, int method, int price, int shift)
   double iFractalsMQL4(string symbol, int tf, int mode, int shift)
   double iGatorMQL4(string symbol, int tf, int jaw_period, int jaw_shift, int teeth_period, int teeth_shift, int lips_period, int lips_shift, int method, int price, int mode, int shift)
   double iIchimokuMQL4(string symbol, int tf, int tenkan_sen, int kijun_sen, int senkou_span_b, int mode, int shift)
   double iMACDMQL4(string symbol, int tf, int fast_ema_period, int slow_ema_period, int signal_period, int price, int mode, int shift)
   double iMAMQL4(string symbol, int tf, int period, int ma_shift, int method, int price, int shift)
   double iMFIMQL4(string symbol, int tf, int period, int shift)
   double iMomentumMQL4(string symbol, int tf, int period, int price, int shift)
   double iOBVMQL4(string symbol, int tf, int price, int shift)
   double iOsMAMQL4(string symbol, int tf, int fast_ema_period, int slow_ema_period, int signal_period, int price, int shift)
   double iRSIMQL4(string symbol, int tf, int period, int price, int shift)
   double iRVIMQL4(string symbol, int tf, int period, int mode, int shift)
   double iSARMQL4(string symbol, int tf, double step, double maximum, int shift)
   double iStdDevMQL4(string symbol, int tf, int ma_period, int ma_shift, int method, int price, int shift)
   double iStochasticMQL4(string symbol, int tf, int Kperiod, int Dperiod, int slowing, int method, int field, int mode, int shift)
   double iWPRMQL4(string symbol, int tf, int period, int shift)

In indicators the manual tweaks are needed for OnInit() function and #property headers. Also IndicatorCounted() function needs to be changed to variable for same name by removing clauses or changing to MQL5 prev_calculated variable:

#define IndicatorCounted IndicatorCountedMQL4(prev_calculated)

In custom indicators please see how #property headers are in MQL5 and then swap input parameters definitions type extern to input. Also in MQL5 they are now constants and any attempt to change values will lead to errors. The fix is by adding temporary variables then copy input parameters values to them instead.

On first line of your base code please add MQL4 reserved variables initialization function (the custom indicators will have warnings about OHLC/Time/Volume reserved variables if they are used in OnCalculate() function, safe to ignore): 

// -- Init MQL4 compatible environment
   InitMQL4Env();