Detecting datatype from a string

[Omega J Msigwa]

Does anyone know a way to detect a datatype from a string value?

This can be important when reading from a CSV file, as we all know mql5 reads a csv file as a data of one type it, for example reading the information from a CSV as strings which works better and gives you the option to convert the data loaded from a file into whatever datatype you intend to, Just like using pandas.read_csv 

matrix ReadCsv(string file_name,string delimiter=",",bool common=false)
  {
   matrix mat_ = {};
   int rows_total=0;
   
   int handle = FileOpen(file_name,FILE_SHARE_READ|FILE_CSV|FILE_ANSI|(common?FILE_COMMON:FILE_ANSI),delimiter);
   
   if(handle == INVALID_HANDLE)
     {
      printf("Invalid %s handle Error %d ",file_name,GetLastError());
      Print(GetLastError()==0?" TIP | File Might be in use Somewhere else or in another Directory":"");
     }

   else
     {
      int column = 0, rows=0;

      while(!FileIsEnding(handle) && !IsStopped())
        {
         string data = FileReadString(handle); 
         
         //---
         
         if(rows ==0)
           {
            ArrayResize(csv_header,column+1);
            csv_header[column] = data;
           }
         
         
         if(rows>0)  //Avoid the first column which contains the column's header
          {
              mat_[rows-1,column] = (double(data));
          }
         
         
         column++;

         //---

         if(FileIsLineEnding(handle))
           {
            rows++;

            mat_.Resize(rows,column);
            
            column = 0;
           }
        }

      rows_total = rows;

      FileClose(handle);
     }
   
   Comment("");
   
   mat_.Resize(rows_total-1,mat_.Cols());

   return(mat_);
  }

I would like to be able to detect the datatype from a string which could have data in different formats like: 

Something like this,

enum dt_type
  {
   DT_DOUBLE_FLOAT_INT,
   DT_DATETIME,
   DT_STRING
  };

dt_type DetectType(string val)
 {
   //if (StringToDouble(val))
   //How can one detect a data type here ???
   
   return DT_DATETIME; //In case datetime was detected
 }

[R4tna C]

Omega J Msigwa:
//if (StringToDouble(val))    //How can one detect a data type here ???

The problem I found with StringToDouble() is that it will return 0.0 for incorrect strings - no easy way of knowing whether it is pass/fail.

For example:

      string test = "AB.12";
      
      double result = StringToDouble(test);
      
      PrintFormat("%s = %f", test, result);

Outputs:

AB.12 = 0.000000

So I think you need to write your own utils to check the strings in detail - I have done that, not just in MQL5 but other languages too whenever I find the standard tools omit something I need. 

This thread has some good examples which may help:

https://www.mql5.com/en/forum/151881

[Omega J Msigwa]

R4tna C #:

Yeah, not to mention converting a string "0.0", will result into 0.0 just like converting "AB.12" leads to 0

[Le Minh Duc]

Omega J Msigwa:

Does anyone know a way to detect a datatype from a string value?

This can be important when reading from a CSV file, as we all know mql5 reads a csv file as a data of one type it, for example reading the information from a CSV as strings which works better and gives you the option to convert the data loaded from a file into whatever datatype you intend to, Just like using pandas.read_csv 

I would like to be able to detect the datatype from a string which could have data in different formats like: 

Something like this,

You can use MqlParam to detect the datatype from a string.
I just found an example for reading file: https://www.mql5.com/en/code/24777