MQL5 Programming for Traders

https://www.mql5.com/en/book
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This book serves as a comprehensive manual for MQL5, the algorithmic trading language for MetaTrader...
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### OnStart function beginning

Source: https://www.mql5.com/en/book/applications/objects/objects_width_height

Starts the main script logic: gets the chart window, displays the corner, and calculates the window dimensions and initial center coordinates.

```cpp
void OnStart() 
{ 
   const int t = ChartWindowOnDropped(); 
   Comment(EnumToString(Corner)); 

   const string name = "ObjSizeLabel"; 
   int h = (int)ChartGetInteger(0, CHART_HEIGHT_IN_PIXELS, t) - 1; 
   int w = (int)ChartGetInteger(0, CHART_WIDTH_IN_PIXELS) - 1; 
   int x = w / 2; 
   int y = h / 2;
```

--------------------------------

### Loop start in OnStart for iHighest example

Source: https://www.mql5.com/en/book/applications/timeseries/timeseries_highest_lowest

Beginning of the main loop in OnStart. It defines the time borders of the current higher timeframe bar using iTime. The rest of the loop is shown in the next snippet.

```mql5
for(int i = 0; i < BarCount; ++i) 
   { 
      const datetime next = iTime(WorkSymbol, TimeFrame, i); 
      const datetime prev = iTime(WorkSymbol, TimeFrame, i + 1); 
      ...
```

--------------------------------

### Usage of ChangeFileReader in OnStart

Source: https://www.mql5.com/en/book/advanced/calendar/calendar_change_last

This example shows how to use the ChangeFileReader class in OnStart. It opens a file, creates a reader, and then loops through the file, calling reader.check on each iteration to get changed news IDs.

```mql5
void OnStart() 
{ 
   const long day = 60 * 60 * 24; 
   datetime now = Start ? Start : (datetime)(TimeCurrent() / day * day); 

   int handle = FileOpen(Filename, 
      FILE_READ | FILE_SHARE_WRITE | FILE_SHARE_READ | FILE_BIN); 
   if(handle == INVALID_HANDLE) 
   { 
      PrintFormat("Can't open file '%s' for reading", Filename); 
      return; 
   } 

   ChangeFileReader reader(handle, now); 

   // reading step by step, time now artificially increased in this demo 
   while(!FileIsEnding(handle)) 
   { 
      // in a real application, a call to reader.check can be made on every tick 
      ulong records[]; 
      if(reader.check(now, records)) 
      { 
         Print(now);          // output time 
         ArrayPrint(records); // array of IDs of changed news 
      } 
      now += 60; // add 1 minute at a time, can be per second 
   } 

   FileClose(handle); 
}
```

--------------------------------

### OnStart example using HTTPSend and HTTPRecv

Source: https://www.mql5.com/en/book/advanced/network/network_socket_send_read

Shows how to use HTTPSend and HTTPRecv in OnStart to send a HEAD request and print the response. Uses PRTF for error reporting and a 5000 ms timeout.

```mql5
void OnStart() 
{ 
      ... 
      if(PRTF(HTTPSend(socket, StringFormat("HEAD / HTTP/1.1\r\nHost: %s \r\n" 
         "User-Agent: MetaTrader 5\r\n\r\n", Server)))) 
      { 
         string response; 
         if(PRTF(HTTPRecv(socket, response, 5000))) 
         { 
            Print(response); 
         } 
      } 
      ... 
}
```

--------------------------------

### StringGetCharacter example

Source: https://www.mql5.com/en/book/common/strings/strings_codepages

Shows how to get the character code at a specific position using StringGetCharacter and the equivalent operator indexing. The example prints the code for '5' (53) using both methods.

```MQL5
string numbers = "0123456789"; 
   PRT(StringGetCharacter(numbers, 5));      // 53 = code '5' 
   PRT(numbers[5]);                          // 53 - is the same
```

--------------------------------

### OnStart example using overloaded operators

Source: https://www.mql5.com/en/book/oop/classes_and_interfaces/classes_operator_overloading

Demonstrates the overloaded operators in a complete OnStart function. It uses prefix and postfix increments, index access, assignment, and prefix decrement, printing results that match expected Fibonacci numbers.

```mql5
void OnStart() 
{ 
   Fibo f1, f2, f3, f4; 
   for(int i = 0; i < 10; ++i, ++f1) // prefix increment 
   { 
      f4 = f3++; // postfix increment and assignment overloading 
   } 

   // compare all values obtained by increments and by index [10] 
   Print(~f1, " ", ~f2[10], " ", ~f3, " ", ~f4); // 89 89 89 55 

   // counting in opposite direction, down to 0 
   Fibo f0; 
   Fibo f = f0[10]; // copy constructor (due to initialization) 
   for(int i = 0; i < 10; ++i) 
   { 
      // prefix decrement 
      Print(~--f); // 55, 34, 21, 13, 8, 5, 3, 2, 1, 1 
   } 
}
```

--------------------------------

### ShortArrayToString example from StringSymbols.mq5

Source: https://www.mql5.com/en/book/common/strings/strings_codepages

Converts part of an array of character codes to a string. The example shows converting an array of size 30 starting at index 0, producing a string that may include random characters beyond the intended content.

```MQL5
string s = ShortArrayToString(array2, 0, 30);
PRT(s); // "ABCDEАБВГД", additional random characters may appear here
```

--------------------------------

### StringSubstr function examples

Source: https://www.mql5.com/en/book/common/strings/strings_find_replace_split

Demonstrates the StringSubstr function for extracting substrings. Shows various start and length parameters, including extracting a fixed length, extracting to the end when length is -1 or too large, and returning an empty string when start is out of range.

```MQL5
PRT(StringSubstr("ABRACADABRA", 4, 3));        // 'CAD' 
PRT(StringSubstr("ABRACADABRA", 4, 100));      // 'CADABRA' 
PRT(StringSubstr("ABRACADABRA", 4));           // 'CADABRA' 
PRT(StringSubstr("ABRACADABRA", 100));         // ''
```

--------------------------------

### OnStart loop to create multiple bitmap labels

Source: https://www.mql5.com/en/book/applications/objects/objects_bitmap_offset

The OnStart function sets the icon size to 46 pixels and loops through 7 icons, calling SetupBitmap for each to place them vertically at the right edge of the window. The same image file is used for all objects, but different offsets display different fragments.

```MQL5
void OnStart() 
{ 
   const int icon = 46; // size of one icon 
   for(int i = 0; i < 7; ++i) // loop through the icons in the file 
   { 
      SetupBitmap(i, 10, 10 + i * icon, icon, 
         "\\Files\\MQL5Book\\icons-322-46.bmp"); 
   } 
}
```

--------------------------------

### OnStart: create table and count records

Source: https://www.mql5.com/en/book/advanced/sqlite/sqlite_example_ts

Opens the database, deletes and recreates the table, then reads bars in chunks and prints the total record count.

```MQL5
void OnStart() 
{ 
   Print(""); 
   DBSQLite db(Database + _Symbol + PeriodToString()); 
   if(!PRTF(db.isOpen())) return; 

   PRTF(db.deleteTable(typename(MqlRatesDB))); 

   if(!PRTF(db.createTable<MqlRatesDB>(true))) return; 
   ...
```

```MQL5
int offset = 0; 
   while(ReadChunk(db, offset, TransactionSize) && !IsStopped()) 
   { 
      offset += TransactionSize; 
   }
```

```MQL5
DBRow *rows[]; 
   if(db.prepare(StringFormat("SELECT COUNT(*) FROM %s", 
      typename(MqlRatesDB))).readAll(rows)) 
   { 
      Print("Records added: ", rows[0][0].integer_value); 
   } 
}
```

--------------------------------

### ObjectTimeframes.mq5 - OnStart with EnumToArray

Source: https://www.mql5.com/en/book/applications/objects/objects_timeframes

Starts the test script by including ObjectPrefix.mqh and MQL5Book/EnumToArray.mqh, then uses EnumToArray to get all timeframe values into an array.

```MQL5
#include "ObjectPrefix.mqh" 
#include <MQL5Book/EnumToArray.mqh> 

void OnStart() 
{ 
   ENUM_TIMEFRAMES tf = 0; 
   int values[]; 
   const int n = EnumToArray(tf, values, 0, USHORT_MAX); 
   ...
```

--------------------------------

### OnStart function calling SetupChannel for three channels

Source: https://www.mql5.com/en/book/applications/objects/objects_rays

This function creates three standard deviation channels with different ray settings: one with right ray only, one with left ray only, and one with no rays. It demonstrates the usage of the SetupChannel helper function.

```mql5
void OnStart() 
{ 
   SetupChannel(24, 1.0, true); 
   SetupChannel(48, 2.0, false, true, clrBlue); 
   SetupChannel(36, 3.0, false, false, clrGreen); 
}
```

--------------------------------

### Plot customization setup

Source: https://www.mql5.com/en/book/applications/indicators_use/indicators_flexible_create

Defines a static array of colors, gets the indicator short name, and calculates the number of buffers to use.

```MQL5
... 
   static color defColors[BUF_NUM] = {clrBlue, clrGreen, clrRed, clrCyan, clrMagenta}; 
   const string s = indicator.getName(); 
   const int n = (IndicatorSelector != iCustom_) ? IND_BUFFERS(IndicatorSelector) : BUF_NUM; 
   ...
```

--------------------------------

### OnStart handler with WebRequest call

Source: https://www.mql5.com/en/book/advanced/network/network_http

Calls WebRequest with the given parameters, logs the response headers, and either saves the response data to a file or prints the first 80 bytes as UTF-8. Uses URL::parse to construct a filename from the host and path.

```MQL5
void OnStart() 
{ 
   uchar data[], result[]; 
   string response; 

   int code = PRTF(WebRequest(Method, Address, Headers, Timeout, data, result, response)); 
   if(code > -1) 
   { 
      Print(response); 
      if(ArraySize(result) > 0) 
      { 
         PrintFormat("Got data: %d bytes", ArraySize(result)); 
         if(DumpDataToFiles) 
         { 
            string parts[]; 
            URL::parse(Address, parts); 

            const string filename = parts[URL_HOST] + 
               (StringLen(parts[URL_PATH]) > 1 ? parts[URL_PATH] : "/_index_.htm"); 
            Print("Saving ", filename); 
            PRTF(FileSave(filename, result)); 
         } 
         else 
         { 
            Print(CharArrayToString(result, 0, 80, CP_UTF8)); 
         } 
      } 
   } 
}
```

--------------------------------

### ObjectCornerLabel.mq5: OnStart initialization and window dimensions

Source: https://www.mql5.com/en/book/applications/objects/objects_corner_x_y

Starts the script by getting the subwindow index from ChartWindowOnDropped(), converting the corner enum to a string for the object name, and retrieving the chart's width and height in pixels. It initializes the label's starting position to the center of the window.

```MQL5
void OnStart() 
{ 
   const int t = ChartWindowOnDropped(); 
   const string legend = EnumToString(Corner); 

   const string name = "ObjCornerLabel-" + legend; 
   int h = (int)ChartGetInteger(0, CHART_HEIGHT_IN_PIXELS, t); 
   int w = (int)ChartGetInteger(0, CHART_WIDTH_IN_PIXELS); 
   int x = w / 2; 
   int y = h / 2; 
   ...
```

--------------------------------

### Prefix and postfix increment examples (ExprIncDec.mq5)

Source: https://www.mql5.com/en/book/basis/expressions/increment_decrement

Shows the difference between prefix (++i) and postfix (i++) increment. In the first line, j gets the new value of i (1) and i becomes 1. In the second line, j gets the old value of i (1) and i becomes 2.

```cpp
int i = 0, j; 
j = ++i;       // j = 1, i = 1 
j = i++;       // j = 1, i = 2
```

--------------------------------

### ARGBbitmap.mq5 script: OnStart function

Source: https://www.mql5.com/en/book/advanced/resources/resources_resourcecreate

Creates the dynamic resource, displays it in a chart object, and waits for ESC to clean up.

```mql5
void OnStart() 
{ 
   ResourceCreate(ResName, Data, ArrayRange(Data, 1), ArrayRange(Data, 0), 
      0, 0, 0, ColorFormat); 

   ObjectCreate(0, BitmapObject, OBJ_BITMAP_LABEL, 0, 0, 0); 
   ObjectSetInteger(0, BitmapObject, OBJPROP_XDISTANCE, 50); 
   ObjectSetInteger(0, BitmapObject, OBJPROP_YDISTANCE, 50); 
   ObjectSetString(0, BitmapObject, OBJPROP_BMPFILE, ResName); 

   Comment("Press ESC to stop the demo"); 
   const ulong start = TerminalInfoInteger(TERMINAL_KEYSTATE_ESCAPE); 
   while(!IsStopped()  // waiting for the user's command to end the demo 
   && TerminalInfoInteger(TERMINAL_KEYSTATE_ESCAPE) == start) 
   { 
      Sleep(1000); 
   } 

   Comment(""); 
   ObjectDelete(0, BitmapObject); 
   ResourceFree(ResName); 
}
```

--------------------------------

### Wrapping OnStart with #define

Source: https://www.mql5.com/en/book/basis/preprocessor/preprocessor_define_simple

Demonstrates how to wrap the original OnStart function by defining a macro that renames it to _OnStart, allowing a header file to add extra actions around the original implementation.

```mql5
void OnStart() 
{ 
   Print("OnStart wrapper started"); 
   // ... additional actions 
   \_OnStart(); 
   // ... additional actions 
   Print("OnStart wrapper stopped"); 
} 

#define OnStart \_OnStart
```

--------------------------------

### Floating-point division: double d = 24.0 / 7;

Source: https://www.mql5.com/en/book/basis/expressions/operators_arithmetic

To get a fractional result, at least one operand must be of real type. This example yields d = 3.4285714285714284.

```mql5
double d = 24.0 / 7; // ok: d = 3.4285714285714284
```

--------------------------------

### OnStart with filter object and branch on ShowPerSymbolDetails

Source: https://www.mql5.com/en/book/automation/symbols/symbols_swaps

The OnStart function creates a SymbolFilter object and prints a header. It then branches based on ShowPerSymbolDetails: if true, it outputs a summary table of swaps for the selected Mode; otherwise, it calculates mode statistics.

```MQL5
void OnStart() 
{ 
   SymbolFilter f;                // filter object 
   PrintFormat("===== Swap modes for %s symbols =====", 
      (UseMarketWatch ? "Market Watch" : "all available")); 

   if(ShowPerSymbolDetails) 
   { 
      // summary table of swaps of the selected Mode 
      ... 
   } 
   else 
   { 
      // calculation of mode statistics 
      ... 
   } 
}
```

--------------------------------

### OnInit timer scheduling for one-time execution

Source: https://www.mql5.com/en/book/automation/experts/experts_market_buy_sell

In OnInit, schedules a delayed start using EventSetTimer(1) so the action runs once on a timer, as in previous examples.

```MQL5
void OnInit()
{
   // scheduling a delayed start
   EventSetTimer(1);
}
```

--------------------------------

### StringToTime usage example from ConversionTime.mq5

Source: https://www.mql5.com/en/book/common/conversions/conversions_datetime

Demonstrates converting strings containing only time, only date, and a long value to datetime. Shows that time-only strings get the current date, date-only strings get time 00:00:00, and casting a long to datetime interprets it as seconds since 1970.

```MQL5
void OnStart()
{
   string timeonly = "21:01";   // time only
   PRT(timeonly);
   PRT((datetime)timeonly);
   PRT(StringToTime(timeonly));

   string date = "2000-10-10";  // date only
   PRT((datetime)date);
   PRT(StringToTime(date));
   PRT((long)(datetime)date);
   long seconds = 60;
   PRT((datetime)seconds); // 1 minute from the beginning of 1970
}
```

--------------------------------

### OnInit handler with Settings initialization

Source: https://www.mql5.com/en/book/automation/experts/experts_multisymbol

Initializes a Settings structure with input parameters and validates it. If valid, prints the settings and proceeds to initialize the trading algorithm.

```MQL5
int OnInit() 
{ 
   Settings settings = 
   { 
      UseTime, HourStart, HourEnd, 
      Lots, Factor, Limit, 
      StopLoss, TakeProfit, 
      StartType, Magic, SkipTimeOnError, Trailing, _Symbol 
   }; 

   if(settings.validate()) 
   { 
      settings.print(); 
      ... 
      // here you will need to initialize the trading algorithm with these settings 
   } 
   ... 
}
```

--------------------------------

### OnStart function for WebSocket echo client

Source: https://www.mql5.com/en/book/advanced/project/project_echo_chat_mql5

Creates a WebSocketClient instance, opens the connection, waits for a welcome message, sends the message, and receives the echo. Uses AutoPtr for automatic memory management.

```MQL5
void OnStart() 
{ 
   Print("\n"); 
   WebSocketClient<Hybi> wss(Server); 
   Print("Opening..."); 
   if(wss.open()) 
   { 
      Print("Waiting for welcome message (if any)"); 
      AutoPtr<IWebSocketMessage> welcome(wss.readMessage()); 
      ...
```

--------------------------------

### Get environment property string (simplified)

Source: https://www.mql5.com/en/book/common/environment/env_signature

Shows how to construct a string describing an environment property, e.g., 'TERMINAL_LANGUAGE=German', using EnumToString and TerminalInfoString. This is a simplified example for illustration.

```mql5
string language = EnumToString(TERMINAL_LANGUAGE) + 
            "=" + TerminalInfoString(TERMINAL_LANGUAGE);
```

--------------------------------

### OnStart function demonstrating pointer usage

Source: https://www.mql5.com/en/book/oop/classes_and_interfaces/classes_ref_pointers_const

Shows how to declare constant and non-constant Counter objects and call the previously defined functions. It includes type casting to bypass const restrictions, with comments indicating errors.

```mql5
void OnStart() 
{ 
   Counter counter; 
   const Counter constCounter; 

   counter.increment(); 

   // ERROR: 
   // constCounter.increment(); // call non-const method for constant object 
   Counter \*ptr = (Counter \*)&constCounter; // trick: type casting without const 
   ptr.increment(); 

   functionVolatile(&counter); 

   // ERROR: cannot convert from a const pointer... 
   // functionVolatile(&constCounter); // to a non-const pointer 

   functionVolatile((Counter \*)&constCounter); // type casting without const 

   functionConst(&counter); 
   functionConst(&constCounter); 

   functionConstConst(&counter); 
   functionConstConst(&constCounter); 
}
```

--------------------------------

### SymbolListSync.mq5: Indicator properties and OnInit timer setup

Source: https://www.mql5.com/en/book/automation/symbols/symbols_sync

Sets up the indicator with no plots and an input parameter SyncCheckupPeriod (seconds) that controls the timer interval. The timer is started in OnInit.

```MQL5
#property indicator_chart_window 
#property indicator_plots 0 

input int SyncCheckupPeriod = 1; // SyncCheckupPeriod (seconds) 

void OnInit() 
{ 
   EventSetTimer(SyncCheckupPeriod); 
}
```

--------------------------------

### Write and read array with FileSave and FileLoad

Source: https://www.mql5.com/en/book/common/files/files_save_load

In the OnStart function, an array of Simple structures is initialized, written to a file using FileSave, read back using FileLoad, and compared with ArrayCompare. The filename includes the MQL5Book subfolder. The expected results are true for FileSave, 2 for FileLoad, and 0 for ArrayCompare.

```MQL5
void OnStart() 
{ 
   Simple write[] = 
   { 
      {+1.0, -1, D'2021.01.01', clrBlue, {'a'}, true, {1000, 16000}}, 
      {-1.0, -2, D'2021.01.01', clrRed,  {'b'}, true, {1000, 16000}}, 
   }; 
   ...
```

```MQL5
const string filename = "MQL5Book/rawdata";
```

```MQL5
PRT(FileSave(filename, write/*, FILE_COMMON*/)); // true 

   Simple read[]; 
   PRT(FileLoad(filename, read/*, FILE_COMMON*/)); // 2 

   PRT(ArrayCompare(write, read)); // 0
```

--------------------------------

### SymbolFilterCurrency.mq5 script setup

Source: https://www.mql5.com/en/book/automation/symbols/symbols_currencies

Starts a script that filters symbols based on base and profit currency. Includes the SymbolFilter.mqh header and an input parameter MarketWatchOnly that defaults to true.

```MQL5
#include <MQL5Book/SymbolFilter.mqh> 

input bool MarketWatchOnly = true; 

void OnStart() 
{ 
   SymbolFilter f;   // filter object 
   string symbols[]; // array for results 
   ...
```

--------------------------------

### OnStart with comment and loop start

Source: https://www.mql5.com/en/book/applications/objects/objects_anchor

Starts the script by displaying the selected corner as a comment on the chart, then enters an infinite loop that will change the anchor point.

```MQL5
void OnStart() 
{ 
   Comment(EnumToString(Corner)); 
   ...
```

--------------------------------

### CryptDecode.mq5 OnStart: key generation and array setup

Source: https://www.mql5.com/en/book/advanced/crypt/crypt_decode

The OnStart function initializes arrays and obtains a key from a string or by simple generation (demo only). The key is used for decryption; for zip and base64, an empty key is suitable. The code prints the key bytes or a message if no key is provided.

```mql5
void OnStart()
{
   ENUM_CRYPT_METHOD method = 0;
   int methods[];
   uchar key[] = {};        // default empty key suitable for zip and base64
   uchar data[], result[];
   uchar zip[], opt[] = {1, 0, 0, 0};

   if(GenerateKey == DUMMY_KEY_CUSTOM)
   {
      if(StringLen(CustomKey))
      {
         PRTF(CustomKey);
         StringToCharArray(CustomKey, key, 0, -1, CP_UTF8);
         ArrayResize(key, ArraySize(key) - 1);
      }
   }
   else if(GenerateKey != DUMMY_KEY_0)
   {
      ArrayResize(key, GenerateKey);
      for(int i = 0; i < GenerateKey; ++i) key[i] = (uchar)i;
   }

   if(ArraySize(key))
   {   
      Print("Key (bytes):");
      ByteArrayPrint(key);
   }
   else
   {
      Print("Key is not provided");
   }
```

--------------------------------

### offsetof operator example

Source: https://www.mql5.com/en/book/oop/structs_and_unions/structs_pack_dll

Shows how to use offsetof(Result, status) to get the byte offset of the status field. The output is 36 because four double values and one int precede it.

```MQL5
Print(offsetof(Result, status)); // 36
```

--------------------------------

### Preparing and executing a query with DBQuery

Source: https://www.mql5.com/en/book/advanced/sqlite/sqlite_crud_examples

Shows how to open a database, prepare a query, get a cursor, and retrieve an array of objects from the query result. This example reads table metadata from the database.

```mql5
DBSQLite db("MQL5Book/DB/Example1");                            // open base 
DBQuery *query = db.prepare("PRAGMA table_xinfo('Struct')");    // prepare the request 
DBRowStruct<DBTableColumn> *row = query.start<DBTableColumn>(); // get object cursor 
DBTableColumn columns[];                                        // receiving array of objects 
while(row.next())             // loop while there are records in the query result 
{ 
   PUSH(columns, row.get());  // getting an object from the current record 
} 
ArrayPrint(columns);
```

--------------------------------

### Print Hello, world in MQL5

Source: https://www.mql5.com/en/book/intro/first_program

Basic MQL5 script that prints "Hello, world" to the Expert Advisors log using the Print function inside OnStart.

```MQL5
void OnStart() 
{ 
  Print("Hello, world"); 
}
```

--------------------------------

### Reservoir.mq5 script - packing data into resource

Source: https://www.mql5.com/en/book/advanced/resources/resources_resourcereadimage

First half of OnStart: creates a Reservoir object, packs a string, a MqlTick structure, and a double number into it, then submits the data to a resource and clears the object.

```MQL5
#include <MQL5Book/Reservoir.mqh> 
#include <MQL5Book/PRTF.mqh> 

void OnStart() 
{ 
   const string resource = "::reservoir"; 

   Reservoir res1; 
   string message = "message1";     // string to write to the resource 
   PRTF(res1.packString(message)); 

   MqlTick tick1[1];                // add a simple structure 
   SymbolInfoTick(_Symbol, tick1[0]); 
   PRTF(res1.packArray(tick1)); 
   PRTF(res1.packNumber(DBL_MAX));  // real number 
   ...
```

```MQL5
res1.submit(resource);           // create a resource with storage data 
   res1.clear();                    // clear the object, but not the resource
```
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