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Filename : gdecl.awk
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#!/usr/bin/mawk -f

# parse a C declaration by recursive descent
# 
#  decl.awk with extra escapes \

################################################
############################################


#   lexical scanner -- gobble()
#   input : string s -- treated as a regular expression
#   gobble eats SPACE, then eats longest match of s off front
#   of global variable line.
#   Cuts the matched part off of line
#


function gobble(s,  x)  
{
  sub( /^ /, "", line)  # eat SPACE if any

  # surround s with parenthesis to make sure ^ acts on the
  # whole thing

  match(line, "^" "(" s ")")
  x = substr(line, 1, RLENGTH)
  line = substr(line, RLENGTH+1)
  return x 
}


function ptr_to(n,  x)  # print "pointer to" , n times
{ n = int(n)
  if ( n <= 0 )  return ""
  x = "pointer to" ; n--
  while ( n-- )  x = x " pointer to"
  return x
}


#recursively get a decl
# returns an english description of the declaration or
# "" if not a C declaration.

function  decl(   x, t, ptr_part)
{

  x = gobble("[* ]+")   # get list of *** ...
  gsub(/ /, "", x)   # remove all SPACES
  ptr_part = ptr_to( length(x) )

  # We expect to see either an identifier or '('
  #

  if ( gobble("\\(") )
  { 
    # this is the recursive descent part
    # we expect to match a declaration and closing ')'
    # If not return "" to indicate  failure

      if ( (x = decl()) == "" || gobble( "\\)" ) == "" ) return ""

  }
  else  #  expecting an identifier
  {
    if ( (x = gobble(id)) == "" )  return ""
    x = x ":"
  }

  # finally look for ()
  # or  [ opt_size ]

  while ( 1 )
     if ( gobble( funct_mark ) )  x = x " function returning"
     else
     if ( t = gobble( array_mark ) )
     { gsub(/ /, "", t)
       x = x " array" t " of"
     }
     else  break


   x = x " "  ptr_part
   return x
}
    

BEGIN { id = "[_A-Za-z][_A-Za-z0-9]*" 
        funct_mark = "\\([ \t]*\\)"
	array_mark = "\\[[ \t]*[_A-Za-z0-9]*[ \t]*\\]"

# I've assumed types are keywords or all CAPS or end in _t
# Other conventions could be added.

    type0 = "int|char|short|long|double|float|void" 
    type1 = "[_A-Z][_A-Z0-9]*"  #  types are CAPS
    type2 = "[_A-Za-z][_A-Za-z0-9]*_t"  # end in _t

    types = "(" type0 "|" type1 "|" type2 ")"
}


{   

    gsub( /\/\*([^*]|\*[^\/])*(\*\/|$)/ , " ") # remove comments
    gsub( /[ \t]+/, " ")  # squeeze white space to a single space


    line = $0

    scope = gobble( "extern|static" )

    if ( type = gobble("(struct|union|enum) ") )
    		type = type gobble(id)  #  get the tag
    else
    {

       type = gobble("(un)?signed ") gobble( types )

    }
    
    if ( ! type )  next
    
    if ( (x = decl()) && gobble( ";") )
    {
      x  =  x " " type
      if ( scope )  x = x " (" scope ")"
      gsub( /  +/, " ", x)  # 
      print x
    }

}