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sub_return_substring_of_string_.htm
Navigation:  Language Reference > 13 - Built-in Functions >====== SUB (return substring of string) ====== Previous pageReturn to chapter overviewNext page

SUB(string,position,length)

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SUB Returns a portion of a string.
string A string constant, variable or expression.
position A integer constant, variable, or expression. If positive, it points to a character position relative to the beginning of the string. If negative, it points to the character position relative to the end of the string (i.e., a position value of -3 points to a position 3 characters from the end of the string). If position is omitted or zero, the default in Clarion Win32 is 1.In Clarion#, position uses a zero-based index. A value of zero (0) points to character position 1, 1 points to 2, etc.
length A numeric constant, variable, or expression of number of characters to return.

The SUB procedure parses out a sub-string from a string by returning length characters from the string, starting at position.

The SUB procedure is similar to the “string slicing” operation on STRING, CSTRING, and PSTRING variables. SUB is less flexible and efficient than string slicing, but SUB is “safer” because it ensures that the operation does not overflow the bounds of the string.

“String slicing” is more flexible than SUB because it may be used on both the destination and source sides of an assignment statement, while the SUB procedure can only be used as the source. It is more efficient because it takes less memory than individual character assignments or the SUB procedure (however, no bounds checking occurs).

To take a “slice” of a string, the beginning and ending character numbers are separated by a colon (:) and placed in the implicit array dimension position within the square brackets ([]) of the string. The position numbers may be integer constants, variables, or expressions. If variables are used, there must be at least one blank space between the variable name and the colon separating the beginning and ending number (to prevent PREfix confusion).

Return Data Type:     STRING

Example:

!SUB('ABCDEFGHI',1,1) returns 'A'
!SUB('ABCDEFGHI',-1,1) returns 'I'
!SUB('ABCDEFGHI',4,3) returns 'DEF'
!Get the file extension using SUB procedure
Extension = SUB(FileName,INSTRING('.',FileName,1,1)+1,3)
!The same operation using string slicing
Extension = FileName[(INSTRING('.',FileName,1,1)+1) : (INSTRING('.',FileName,1,1)+3)]
!
IF FILEDIALOG('Pick file',FileName)
  IF SUB(FileName,1,2)='\\' THEN
     STOP('\\UNC paths are not supported!')
  ELSIF UPPER(SUB(FileName,1,11))='C:\WINDOWS\' THEN
     STOP('Do not select Windows folder!')
  END
END
IF FILEDIALOG('Pick file',FileName)
  CASE UPPER(SUB(CLIP(FileName),-4,4))  !Note CLIP(), else get trailing spaces
  OF '.TPS' ; DO TPS_File
  OF '.DBF' ; DO DBase_File
  OF '.CSV' ; DO Text_File
  ELSE
     Message('Unknown file type ' & RIGHT(FileName,4))
  END
END

See Also:

LEFT

RIGHT

INSTRING

STRING

CSTRING

PSTRING

String Slicing

sub_return_substring_of_string_.htm.txt · Last modified: 2021/04/15 15:57 (external edit)