Info Catalog eintr: zap-to-char body eintr: zap-to-char eintr: progn

eintr: search-forward

 
 8.1.3 The ‘search-forward’ Function
 -----------------------------------
 
 The ‘search-forward’ function is used to locate the zapped-for-character
 in ‘zap-to-char’.  If the search is successful, ‘search-forward’ leaves
 point immediately after the last character in the target string.  (In
 ‘zap-to-char’, the target string is just one character long.
 ‘zap-to-char’ uses the function ‘char-to-string’ to ensure that the
 computer treats that character as a string.)  If the search is
 backwards, ‘search-forward’ leaves point just before the first character
 in the target.  Also, ‘search-forward’ returns ‘t’ for true.  (Moving
 point is therefore a side effect.)
 
    In ‘zap-to-char’, the ‘search-forward’ function looks like this:
 
      (search-forward (char-to-string char) nil nil arg)
 
    The ‘search-forward’ function takes four arguments:
 
   1. The first argument is the target, what is searched for.  This must
      be a string, such as ‘"z"’.
 
      As it happens, the argument passed to ‘zap-to-char’ is a single
      character.  Because of the way computers are built, the Lisp
      interpreter may treat a single character as being different from a
      string of characters.  Inside the computer, a single character has
      a different electronic format than a string of one character.  (A
      single character can often be recorded in the computer using
      exactly one byte; but a string may be longer, and the computer
      needs to be ready for this.)  Since the ‘search-forward’ function
      searches for a string, the character that the ‘zap-to-char’
      function receives as its argument must be converted inside the
      computer from one format to the other; otherwise the
      ‘search-forward’ function will fail.  The ‘char-to-string’ function
      is used to make this conversion.
 
   2. The second argument bounds the search; it is specified as a
      position in the buffer.  In this case, the search can go to the end
      of the buffer, so no bound is set and the second argument is ‘nil’.
 
   3. The third argument tells the function what it should do if the
      search fails—it can signal an error (and print a message) or it can
      return ‘nil’.  A ‘nil’ as the third argument causes the function to
      signal an error when the search fails.
 
   4. The fourth argument to ‘search-forward’ is the repeat count—how
      many occurrences of the string to look for.  This argument is
      optional and if the function is called without a repeat count, this
      argument is passed the value 1.  If this argument is negative, the
      search goes backwards.
 
    In template form, a ‘search-forward’ expression looks like this:
 
      (search-forward "TARGET-STRING"
                      LIMIT-OF-SEARCH
                      WHAT-TO-DO-IF-SEARCH-FAILS
                      REPEAT-COUNT)
 
    We will look at ‘progn’ next.
 

Info Catalog eintr: zap-to-char body eintr: zap-to-char eintr: progn