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   6 <TITLE>The SUIF Version 1 Library - Symbol Features</TITLE>
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  17 <H2><A NAME="SEC52" HREF="suif1_toc.html#TOC52">Basic Features of Symbols</A></H2>
  18
  19 <P>
  20 <A NAME="IDX336"></A>
  21 <A NAME="IDX337"></A>
  22 The <CODE>sym_node</CODE> class defines several fields that are used by all
  23 kinds of symbols.  The most obvious of these is the symbol name.  Each
  24 symbol has a name that should be unique within the symbol table where it
  25 is defined.  The <CODE>name</CODE> and <CODE>set_name</CODE> methods access this
  26 field.  The names are automatically entered in the lexicon
  27 (see section <A HREF="suif1_102.html#SEC102">Lexicon</A>) by <CODE>set_name</CODE>.  Because the name of a symbol
  28 alone is generally insufficient to uniquely identify it, the symbols are
  29 also given ID numbers.  See section <A HREF="suif1_50.html#SEC50">Numbering Types and Symbols</A>.
  30
  31 </P>
  32 <P>
  33 <A NAME="IDX338"></A>
  34 When a symbol is entered in a symbol table, it automatically records a
  35 pointer to that parent table.  Similarly, when the symbol is removed
  36 from the symbol table, its parent pointer is cleared.  The <CODE>parent</CODE>
  37 method retrieves this parent pointer.
  38
  39 </P>
  40 <P>
  41 <A NAME="IDX339"></A>
  42 <A NAME="IDX340"></A>
  43 <A NAME="IDX341"></A>
  44 All symbols contain flags to specify various attributes.  The
  45 <CODE>sym_node</CODE> class provides methods to access these flags.  The
  46 <CODE>is_userdef</CODE> method tests a flag to see if it is a user-defined
  47 symbol (from the source code) or a new symbol introduced by the
  48 compiler.  The <CODE>set_userdef</CODE> and <CODE>reset_userdef</CODE> methods
  49 change the value of this flag.
  50
  51 </P>
  52 <P>
  53 <A NAME="IDX342"></A>
  54 Another flag is used to mark symbols that are only declarations of
  55 external symbols, rather than actual definitions.  This flag is set
  56 automatically.  The <CODE>is_extern</CODE> method retrieves its value.  Label
  57 symbols are never <CODE>extern</CODE>.  A procedure symbol is <CODE>extern</CODE>
  58 unless the procedure body is defined in the input file(s).  A global
  59 variable symbol is <CODE>extern</CODE> unless it has a separate definition
  60 (see section <A HREF="suif1_58.html#SEC58">Variable Definitions</A>); no other variables are <CODE>extern</CODE>.
  61
  62 </P>
  63 <P>
  64 <A NAME="IDX343"></A>
  65 <A NAME="IDX344"></A>
  66 Since symbols may be treated differently depending on their scopes, the
  67 <CODE>sym_node</CODE> class includes methods to determine which kind of symbol
  68 table contains a symbol.  The <CODE>is_global</CODE> method checks if the
  69 parent table is a global or file symbol table.  This is really only
  70 useful for variable symbols, because procedures are always global and
  71 labels are never global.  The <CODE>is_private</CODE> method checks if a
  72 symbol is global but private to one source file by checking if the
  73 parent symbol table is a file symbol table.  This is obviously
  74 irrelevant for label symbols.
  75
  76 </P>
  77 <P>
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  79 <A NAME="IDX346"></A>
  80 The <CODE>add_to_table</CODE> and <CODE>remove_from_table</CODE> methods are
  81 provided for convenience when adding or removing symbols from symbol
  82 tables.  In the case of variable symbols, the entire hierarchy of
  83 sub-variables (see section <A HREF="suif1_57.html#SEC57">Sub-Variables</A>) is added or removed at one time
  84 by this method.
  85
  86 </P>
  87 <P>
  88 <A NAME="IDX347"></A>
  89 The <CODE>copy</CODE> method makes a copy of a symbol.  This is a virtual
  90 function so it copies the fields that are specific to each kind of
  91 symbol.  However, it only copies the symbol itself: copying a procedure
  92 symbol will not copy the procedure body and copying a variable symbol
  93 will not copy the variable definition.  The <CODE>copy</CODE> method does not
  94 copy annotations on the symbol, either.  Since the copy will have the
  95 same name as the original symbol, it should generally be renamed or used
  96 in a different symbol table.
  97
  98 </P>
  99 <P>
 100 <A NAME="IDX348"></A>
 101 <A NAME="IDX349"></A>
 102 Two different methods are available for printing symbols.  The
 103 <CODE>print</CODE> method just prints the name of the symbol.  Label symbols
 104 are prefixed by <SAMP>`L:'</SAMP> and procedure symbols by <SAMP>`P:'</SAMP> to
 105 distinguish them from variable symbols.  The <CODE>print_full</CODE> method is
 106 used by the library when listing the contents of symbol tables.  It
 107 includes all the fields from the <CODE>sym_node</CODE>.
 108
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