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Annotation of coherent/a/usr/man/ALL/_23define, revision 1.1

1.1     ! root        1: 
        !             2: 
        !             3: #define              Preprocessing Directive              #define
        !             4: 
        !             5: 
        !             6: 
        !             7: 
        !             8: Define an identifier as a macro
        !             9: 
        !            10: #ddeeffiinnee _i_d_e_n_t_i_f_i_e_r _l_p_a_r_e_n _i_d_e_n_t_i_f_i_e_r-_l_i_s_t9_o_p_t8 ) _r_e_p_l_a_c_e_m_e_n_t-_l_i_s_t
        !            11: 
        !            12: The preprocessing  directive #define tells the  C preprocessor to
        !            13: regard identifier as a macro.
        !            14: 
        !            15: #define  can  define   two  kinds  of  macros:  object-like,  and
        !            16: function-like.
        !            17: 
        !            18: An object-like macro has the syntax
        !            19: 
        !            20: 
        !            21:         #define _i_d_e_n_t_i_f_i_e_r _r_e_p_l_a_c_e_m_e_n_t-_l_i_s_t
        !            22: 
        !            23: 
        !            24: This  type of  macro  is also  called a  manifest constant.   The
        !            25: preprocessor searches  for identifier throughout the  text of the
        !            26: translation  unit,   and  replaces   it  with  the   elements  of
        !            27: replacement-list, which is  then rescanned for further macro sub-
        !            28: stitutions.
        !            29: 
        !            30: For example, consider the directive:
        !            31: 
        !            32: 
        !            33:         #define BUFFERSIZE 75
        !            34: 
        !            35: 
        !            36: When the preprocessor reads the line
        !            37: 
        !            38: 
        !            39:         malloc(BUFFERSIZE);
        !            40: 
        !            41: 
        !            42: it replaces it with:
        !            43: 
        !            44: 
        !            45:         malloc(75);
        !            46: 
        !            47: 
        !            48: A given identifier is  replaced only once by a given replacement-
        !            49: list.  This is to prevent such code as
        !            50: 
        !            51: 
        !            52:         #define FOO FOO
        !            53: 
        !            54: 
        !            55: or
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        !            60: 
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        !            62: 
        !            63: 
        !            64: COHERENT Lexicon                                           Page 1
        !            65: 
        !            66: 
        !            67: 
        !            68: 
        !            69: #define              Preprocessing Directive              #define
        !            70: 
        !            71: 
        !            72: 
        !            73:         #define FOO BAR
        !            74:         #define BAR FOO
        !            75: 
        !            76: 
        !            77: from generating an infinite loop.
        !            78: 
        !            79: A function-like macro is more complex.  It has the syntax:
        !            80: 
        !            81: 
        !            82:         #define _i_d_e_n_t_i_f_i_e_r _l_p_a_r_e_n _i_d_e_n_t_i_f_i_e_r-_l_i_s_t9_o_p_t8 ) _r_e_p_l_a_c_e_m_e_n_t-_l_i_s_t
        !            83: 
        !            84: 
        !            85: The  preprocessor looks  for identifier,  which  is a  macro that
        !            86: resembles a function  in that it is followed by  a pair of paren-
        !            87: theses that  may enclose  an identifier-list.  It  replaces iden-
        !            88: tifier  with the  contents of replacement-list,  up to  the first
        !            89: lparen `(' within replacement-list.
        !            90: 
        !            91: The preprocessor  then examines identifier-list  for further mac-
        !            92: ros,  which it  expands.   The modified  identifier-list is  then
        !            93: replaced with the rest of replacement-list.  Pairs of parentheses
        !            94: that are  nested between the lparen  that begins replacement-list
        !            95: and  the `)'  that  ends it  are copied  into identifier-list  as
        !            96: literal characters.   The identifiers within  identifier-list are
        !            97: preserved after  it has  been modified by  replacement-list.  The
        !            98: only  exceptions  are   identifiers  that  are  prefixed  by  the
        !            99: preprocessing operators # or ##; these are handled appropriately.
        !           100: 
        !           101: For example, the consider the macro:
        !           102: 
        !           103: 
        !           104:         #define display(x) show((long)(x), #x)
        !           105: 
        !           106: 
        !           107: When the preprocessor reads the following line
        !           108: 
        !           109: 
        !           110:         display(abs(-5));
        !           111: 
        !           112: 
        !           113: it replaces it with the following:
        !           114: 
        !           115: 
        !           116:         show((long)(abs(-5)), "abs(-5)");
        !           117: 
        !           118: 
        !           119: When an argument  to a function-like macro contains no preproces-
        !           120: sing tokens,  or when an  argument to a  function-like macro con-
        !           121: tains a preprocessing  token that is identical to a preprocessing
        !           122: directive, the behavior is undefined.
        !           123: 
        !           124: ***** Example *****
        !           125: 
        !           126: For an  example of using a function-like macro  in a program, see
        !           127: #.
        !           128: 
        !           129: 
        !           130: COHERENT Lexicon                                           Page 2
        !           131: 
        !           132: 
        !           133: 
        !           134: 
        !           135: #define              Preprocessing Directive              #define
        !           136: 
        !           137: 
        !           138: 
        !           139: 
        !           140: ***** See Also *****
        !           141: 
        !           142: #, ##, #undef, C preprocessor
        !           143: 
        !           144: ***** Notes *****
        !           145: 
        !           146: A macro expansion always occupies exactly one line, no matter how
        !           147: many  lines   are  spanned  by  the   definition  or  the  actual
        !           148: parameters.  If  you have defined macros that  span more than one
        !           149: line, you must either redefine  them to occupy one line, or some-
        !           150: how embed  the newline character within  the macro itself; other-
        !           151: wise, the macro will not expand correctly.
        !           152: 
        !           153: A macro  definition can extend over more  than one line, provided
        !           154: that a  backslash `\' appears  before the newline  character that
        !           155: breaks the  lines.  The size of a  #define directive is therefore
        !           156: limited by  the maximum size of a logical  source line, which can
        !           157: be up to at least 509 characters long.
        !           158: 
        !           159: Some implementations  allowed a user to re-define  a macro with a
        !           160: new  #define directive.   The  Standard, however,  allows only  a
        !           161: ``benign'' redefinition; that  is, the body of the new definition
        !           162: must exactly match  the old definition, including parameter names
        !           163: and white space.
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        !           196: COHERENT Lexicon                                           Page 3
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