Synopsis:

       partial_string=strsub(str,start_pos[,end_pos])

Arguments:

       str - The string to extract partial string from

       start_pos - The starting position from which to extract the partial string (first character is numbered 1)

       [end_pos] - Optional ending position for the partial string extraction

Description:  This function extracts a partial string from the given str using the start_pos and end_pos to specified the offsets in the str from which to obtain the partial string to return.        The start_pos must hold a value between 1 and the total number or characters in the string.     The optional end_pos should hold a value between 1 and the total number or characters in the string and must be greater than or equal to the start_pos.    If end_pos is not specified then it defaults to the offset of the last character in the given string and so the partial string returned will be from the start_pos to the end of the given str.

If invalid start_pos or end_pos values are given (such as negative values, start_pos > end_pos, start_pos past end of string etc) then the function will return an empty string.

For example:

       string="ABC123ZYX"

       // This will return ABC

       part_str=strsub(string,1,3);

       // This will return 123

       part_str=strsub(string,4,6);

       // This will return A

       part_str=strsub(string,1,1);

       // This will return 123ZYZ

       part_str=strsub(string,4);

 

       

Returns:  Returns the partial string as sepcifed by the start_pos and end_pos or an empty string if invalid parameters are passed.