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elisp: Modifying Strings

 
 4.4 Modifying Strings
 =====================
 
 The most basic way to alter the contents of an existing string is with
 ‘aset’ (Array Functions).  ‘(aset STRING IDX CHAR)’ stores CHAR
 into STRING at index IDX.  Each character occupies one or more bytes,
 and if CHAR needs a different number of bytes from the character already
 present at that index, ‘aset’ signals an error.
 
    A more powerful function is ‘store-substring’:
 
  -- Function: store-substring string idx obj
      This function alters part of the contents of the string STRING, by
      storing OBJ starting at index IDX.  The argument OBJ may be either
      a character or a (smaller) string.
 
      Since it is impossible to change the length of an existing string,
      it is an error if OBJ doesn’t fit within STRING’s actual length, or
      if any new character requires a different number of bytes from the
      character currently present at that point in STRING.
 
    To clear out a string that contained a password, use ‘clear-string’:
 
  -- Function: clear-string string
      This makes STRING a unibyte string and clears its contents to
      zeros.  It may also change STRING’s length.
 

Info Catalog elisp: Creating Strings elisp: Strings and Characters elisp: Text Comparison