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1.1 root 1: August 25, 1978
2:
3: Files in this directory form the C preprocessor, which handles '#include'
4: files and macro definition and expansion for the C compiler.
5: This new version was written by John F. Reiser and is from 5 to 12
6: times faster (on UNIX systems) than the old.
7:
8: To create the executable file 'cpp' in the current directory:
9: make
10:
11: To install the preprocessor 'cpp' so it will be used by the C compiler:
12: : safety first: backup the existing version
13: cp /lib/cpp /lib/ocpp
14: : install the new version
15: cp cpp /lib/cpp
16:
17: Invocation
18: cpp [-CEPR] [-Dname] ... [-Dname=def] ... [-Idirectory] ...
19: [-Uname] ... [<infile>] [<outfile>]
20:
21: If there are two non-flag arguments then the first is the name of the
22: input file and the second is the name of the output file. If there is
23: one non-flag argument then it is the name of the input file and the
24: output is written on the standard output. If there are no non-flag
25: arguments then the input is taken from the standard input and the output
26: is written on the standard output. Flag arguments are:
27:
28: -C retain comments in output
29: -Dname define name as "1"
30: -Dname=def define name as def
31: -E ignored
32: -Idirectory add directory to search list for #include files
33: -P don't insert lines "# 12 \"foo.c\"" into output
34: -R allow recursive macros
35: -Uname undefine name
36:
37: Documentation clarifications:
38: Symbols defined on the command line by "-Dfoo" are defined as "1",
39: i.e., as if they had been defined by "#define foo 1" or "-Dfoo=1".
40: The directory search order for #include files is
41: 1) the directory of the file which contains the #include request
42: (e.g. #include is relative to the file being scanned when
43: the request is made)
44: 2) the directories specified by -I, in left-to-right order
45: 3) the standard directory(s) (which for UNIX is /usr/include)
46: An unescaped linefeed (the single character "\n") terminates a
47: character constant or quoted string.
48: An escaped linefeed (the two-character sequence "\\\n") may be
49: used in the body of a '#define' statement to continue
50: the definition onto the next line. The escaped linefeed is
51: not included in the macro body.
52: Comments are uniformly removed (except if the argument -C is specified).
53: They are also ignored, except that a comment terminates a token.
54: Thus "foo/* la di da */bar" may expand 'foo' and 'bar' but
55: will never expand 'foobar'. If neither 'foo' nor 'bar' is a
56: macro then the output is "foobar", even if 'foobar'
57: is defined as something else. The file
58: #define foo(a,b)b/**/a
59: foo(1,2)
60: produces "21" because the comment causes a break which enables
61: the recognition of 'b' and 'a' as formals in the string "b/**/a".
62: Macro formal parameters are recognized in '#define' bodies even inside
63: character constants and quoted strings. The output from
64: #define foo(a) '\a'
65: foo(bar)
66: is the seven characters " '\\bar'". Macro names are not recognized
67: inside character constants or quoted strings during the regular scan.
68: Thus
69: #define foo bar
70: printf("foo");
71: does not expand 'foo' in the second line, because it is inside
72: a quoted string which is not part of a '#define' macro definition.
73: Macros are not expanded while processing a '#define' or '#undef'.
74: Thus
75: #define foo bletch
76: #define bar foo
77: #undef foo
78: bar
79: produces "foo". The token appearing immediately after a
80: '#ifdef' or '#ifndef' is not expanded (of course!).
81: Macros are not expanded during the scan which determines the actual
82: parameters to another macro call. Thus
83: #define foo(a,b)b a
84: #define bar hi
85: foo(bar,
86: #define bar bye
87: )
88: produces " bye" (and warns about the redefinition of 'bar').
89:
90: There are some differences between the new and the old preprocessor.
91: Bugs fixed:
92: "1.e4" is recognized as a floating-point number, rather than as an
93: opportunity to expand the possible macro name "e4".
94: Any kind and amount of white space (space, tab, linefeed, vertical tab,
95: formfeed, carriage return) is allowed between a macro name and
96: the left parenthesis which introduces its actual parameters.
97: The comma operator is legal in preprocessor '#if' statements.
98: Macros with parameters are legal in preprocessor '#if' statements.
99: Single-character character constants are legal in preprocessor '#if' statements.
100: Linefeeds are put out in the proper place when a multiline comment
101: is not passed through to the output.
102: The following example expands to "# # #" :
103: #define foo #
104: foo foo foo
105: If the -R flag is not specified then the invocation of some recursive
106: macros is trapped and the recursion forcibly terminated with an
107: error message. The recursions that are trapped are the ones
108: in which the nesting level is non-decreasing from some point on.
109: In particular,
110: #define a a
111: a
112: will be detected. (Use "#undef a" if that is what you want.)
113: The recursion
114: #define a c b
115: #define b c a
116: #define c foo
117: a
118: will not be detected because the nesting level decreases after
119: each expansion of "c".
120: The -R flag specifically allows recursive macros and recursion will
121: be strictly obeyed (to the extent that space is available).
122: Assuming that -R is specified:
123: #define a a
124: a
125: causes an infinite loop with very little output. The tail recursion
126: #define a <b
127: #define b >a
128: a
129: causes the string "<>" to be output infinitely many times. The
130: non-tail recursion
131: #define a b>
132: #define b a<
133: a
134: complains "too much pushback", dumps the pushback, and continues
135: (again, infinitely).
136:
137: Stylistic choice:
138: Nothing (not even linefeeds) is output while a false '#if', '#ifdef',
139: or '#ifndef' is in effect. Thus when all conditions become true
140: a line of the form "# 12345 \"foo.c\"" is output (unless -P).
141: Error and warning messages always appear on standard error (file
142: descriptor 2).
143: Mismatch between the number of formals and actuals in a macro call
144: produces only a warning, and not an error. Excess actuals
145: are ignored; missing actuals are turned into null strings.
146:
147: Incompatibility:
148: The virgule '/' in "a=/*b" is interpreted as the first character of
149: the pair "/*" which introduces a comment, rather than as the
150: second character of the divide-and-replace operator "=/".
151: This incompatibility reflects the recent change in the C language
152: which made "a/=*b" the legal way to write such a statement
153: if the meaning "a=a/ *b" is intended.
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