跳至内容

FileReadInteger

FileReadInteger

此函数根据指定的字节数,从文件指针的当前位置读取 int、short 或 char 类型的值。

int  FileReadInteger(
   int  file_handle,        // File handle
   int  size=INT_VALUE      // Size of an integer in bytes
   );

参数

file_handle

[in] 由 FileOpen() 返回的文件描述符。

size=INT_VALUE

[in] 需要读取的字节数(最多包含 4 个字节)。相应的常量如下:CHAR_VALUE = 1,SHORT_VALUE = 2,INT_VALUE(LONG_VALUE) = 4,因此该函数可以读取 char、short、int 或 long 类型的值。

返回值

int 类型的值。此函数的结果必须显式转换为目标类型,即需要读取的数据类型。由于返回的是 int 类型的值,因此可以轻松将其转换为任何整数值。文件指针会向后移动读取的字节数。

注意

当读取的字节数少于 4 个时,接收的结果总是正数。如果读取了 1 或 2 个字节,可以通过显式转换为 char(1 个字节)或 short(2 个字节)来确定数的符号。获取 3 个字节数的符号并不简单,因为不存在相应的底层类型

示例(此处使用了执行 FileWriteInteger() 函数后得到的文件)

//+------------------------------------------------------------------+
//|                                         Demo_FileReadInteger.mq4 |
//|                        Copyright 2014, MetaQuotes Software Corp. |
//|                                              https://www.mql5.com |
//+------------------------------------------------------------------+
#property copyright "Copyright 2014, MetaQuotes Software Corp."
#property link      "https://www.mql5.com"
#property version   "1.00"
#property strict
#property indicator_chart_window
#property indicator_buffers 1
//---- plot Label1
#property indicator_label1  "Trends"
#property indicator_type1   DRAW_SECTION
#property indicator_color1  clrRed
#property indicator_style1  STYLE_SOLID
#property indicator_width1  2
//--- parameters for data reading
input string InpFileName="Trend.bin"; // File name
input string InpDirectoryName="Data"; // Folder name
//--- global variables
int      ind=0;
int      size=0;
datetime time_buff[];
//--- indicator buffers
double   buff[];
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit()
  {
   int def_size=100;
//--- allocate memory for the array
   ArrayResize(time_buff,def_size);
//--- open the file
   ResetLastError();
   int file_handle=FileOpen(InpDirectoryName+"//"+InpFileName,FILE_READ|FILE_BIN);
   if(file_handle!=INVALID_HANDLE)
     {
      PrintFormat("%s file is available for reading",InpFileName);
      PrintFormat("File path: %s\\Files\\",TerminalInfoString(TERMINAL_DATA_PATH));
      //--- additional variables
      int    arr_size;
      uchar  arr[];
      //--- read data from the file
      while(!FileIsEnding(file_handle))
        {
         //--- find out how many bytes are used for writing the time
         arr_size=FileReadInteger(file_handle,INT_VALUE);
         ArrayResize(arr,arr_size);
         for(int i=0;i<arr_size;i++)
            arr[i]=(char)FileReadInteger(file_handle,CHAR_VALUE);
         //--- store the time value
         time_buff[size]=StringToTime(CharArrayToString(arr));
         size++;
         //--- increase the sizes of the arrays if they are filled
         if(size==def_size)
           {
            def_size+=100;
            ArrayResize(time_buff,def_size);
           }
        }
      //--- close the file
      FileClose(file_handle);
      PrintFormat("Data is read, %s file is closed",InpFileName);
     }
   else
     {
      PrintFormat("Failed to open %s file, Error code = %d",InpFileName,GetLastError());
      return(INIT_FAILED);
     }
//--- bind the array to the indicator buffer
   SetIndexBuffer(0,buff,INDICATOR_DATA);
//---- set the indicator values that will not be visible on the chart
   SetIndexEmptyValue(0,0.0);
//--- set indexing as timeseries
   ArraySetAsSeries(time_buff,true);
//---
   return(INIT_SUCCEEDED);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
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[])
  {
   ArraySetAsSeries(time,true);
   ArraySetAsSeries(close,true);
//--- the loop for the bars that have not been handled yet
   for(int i=prev_calculated;i<rates_total;i++)
     {
      //--- 0 by default
      buff[i]=0;
      for(int j=0;j<size;j++)
        {
         //--- if dates coincide, set as close price
         if(time[i]==time_buff[j])
           {
            //--- set as close price
            buff[i]=close[i];
           }
        }
     }
//---
   return(rates_total);
  }

另请参阅

IntegerToString()StringToInteger()整数类型FileWriteInteger()

最后更新于