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mql4mt4

How to avoid array out of range

Does somebody know how to avoid the error array out of range when trying to display long number of bars (lets say 7000) in an indicator buffer?

Solution

  • While the arrays (problem) look similar, there is a major difference

    MQL4 Indicators use "other" mechanics for handling arrays than "ordinary" arrays have.

    ...  Testing pass stopped due to a critical error in the EA
...  array out of range in '!2015-09-08___!EA 2xAMA 01 2015-09-08_msMOD_0.00.mq4' (519,39)

    Yes, MT4 throws Fatal Error on an attempt to handle a wrong ptr->array[aStaticSIZE] and one has to take due care to either avoid such case, or trim ptr ( alike in low-latency circular-buffer scenarios ) not to direct past the array boundary ( underflow / overflow ) or extend the array[] via ArrayResize() so as to keep pace with the ptr growth ( until memory allows ) ) on arrays declared as dynamic double Array[];, however MQL4 Technical Indicators have completely other situation.

    Limits? Yes. . . . . . ( And one ought to review on each New-MQL4.56789 stealth update )

    As of a "New"-MQL4.56789-Build-840, your "ordinary" array cannot have more than 2.147.483.647 elements, if O/S memory-pool manager allows, so you ought to have plenty of space, even if using higher dimensionality mappings { 2D | 3D | 4D }.

    Years ago 've used many parallel 2D / 3D-arrays for fast and private ( safely encapsulated ) heap / stack-handlers for maintaining highly dynamic entities in scales of 100k+ rows / 2D-planes and all worked well-oiled in old-MQL4.

    So some 7k+ elements should not make you any worries.

    Indicators use array indirectly, via an automated Buffer-handler

    In this sense, your code need not care about these issues.

    /*
#property "pragmas" help MQL4-compiler decide about setup of internal handlers
          so this part of code "speaks" to MetaLang.exe at compile-time*/

#property indicator_buffers      3             // .DEF N-Buffs

#property indicator_color1       White         // .SET Buf[0].color
#property indicator_color2       SeaGreen      // .SET Buf[1].color
#property indicator_color3       FireBrick     // .SET Buf[2].color

#property indicator_width1       1             // .SET Buf[0].width
#property indicator_width2       2             // .SET Buf[1].width
#property indicator_width3       2             // .SET Buf[2].width

         double   buffer_line_up[],            // .DEF Arrays as dynamic ...[]
                  buffer_line_dn[],            //      with human-readable-names
                  buffer_line_ax[];            //      and MT4 will take care

int   init()   {

      SetIndexBuffer(   0, buffer_line_ax );   // .ASSOC IndexBuffer.0<-array[]
      SetIndexLabel(    0, "SuperTrend"     );

      SetIndexBuffer(   1, buffer_line_up   ); // .ASSOC IndexBuffer.0<-array[]
      SetIndexLabel(    1, "Up Trend"       );
      SetIndexStyle(    1, DRAW_LINE,
                           STYLE_SOLID,
                           1 + int( ATR_Multiplier / 5 ),
                           SeaGreen
                           );

      SetIndexBuffer(   2, buffer_line_dn );   // .ASSOC IndexBuffer.0<-array[]
      SetIndexLabel(    2, "Down Trend"     );
      SetIndexStyle(    2, DRAW_LINE,
                           STYLE_SOLID,
                           1 + int( ATR_Multiplier / 5 ),
                           FireBrick
                           );

      SetIndexDrawBegin(0, ATR_Period );       // .DEF initial depth of Buffer before 1st GUI output

      IndicatorShortName( "xxxx[" + ATR_Period + "," + ATR_Multiplier + "]" );

      IndicatorDigits( MarketInfo( Symbol(), MODE_DIGITS ) );