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1.1 root 1: #
2: # @(#)README 1.2 8/30/82
3: #
4: August 30, 1982
5: Fixed by Kurt Shoens, UCB
6: If the "#line n name" occurs, then all future references
7: to the current file are generated in terms of "name", instead
8: of the name of file given to cpp in its command argument
9:
10: August 25, 1978
11:
12: Files in this directory form the C preprocessor, which handles '#include'
13: files and macro definition and expansion for the C compiler.
14: This new version was written by John F. Reiser and is from 5 to 12
15: times faster (on UNIX systems) than the old.
16:
17: To create the executable file 'cpp' in the current directory:
18: make
19:
20: To install the preprocessor 'cpp' so it will be used by the C compiler:
21: : safety first: backup the existing version
22: cp /lib/cpp /lib/ocpp
23: : install the new version
24: cp cpp /lib/cpp
25:
26: Invocation
27: cpp [-CEPR] [-Dname] ... [-Dname=def] ... [-Idirectory] ...
28: [-Uname] ... [<infile>] [<outfile>]
29:
30: If there are two non-flag arguments then the first is the name of the
31: input file and the second is the name of the output file. If there is
32: one non-flag argument then it is the name of the input file and the
33: output is written on the standard output. If there are no non-flag
34: arguments then the input is taken from the standard input and the output
35: is written on the standard output. Flag arguments are:
36:
37: -C retain comments in output
38: -Dname define name as "1"
39: -Dname=def define name as def
40: -E ignored
41: -Idirectory add directory to search list for #include files
42: -P don't insert lines "# 12 \"foo.c\"" into output
43: -R allow recursive macros
44: -Uname undefine name
45:
46: Documentation clarifications:
47: Symbols defined on the command line by "-Dfoo" are defined as "1",
48: i.e., as if they had been defined by "#define foo 1" or "-Dfoo=1".
49: The directory search order for #include files is
50: 1) the directory of the file which contains the #include request
51: (e.g. #include is relative to the file being scanned when
52: the request is made)
53: 2) the directories specified by -I, in left-to-right order
54: 3) the standard directory(s) (which for UNIX is /usr/include)
55: An unescaped linefeed (the single character "\n") terminates a
56: character constant or quoted string.
57: An escaped linefeed (the two-character sequence "\\\n") may be
58: used in the body of a '#define' statement to continue
59: the definition onto the next line. The escaped linefeed is
60: not included in the macro body.
61: Comments are uniformly removed (except if the argument -C is specified).
62: They are also ignored, except that a comment terminates a token.
63: Thus "foo/* la di da */bar" may expand 'foo' and 'bar' but
64: will never expand 'foobar'. If neither 'foo' nor 'bar' is a
65: macro then the output is "foobar", even if 'foobar'
66: is defined as something else. The file
67: #define foo(a,b)b/**/a
68: foo(1,2)
69: produces "21" because the comment causes a break which enables
70: the recognition of 'b' and 'a' as formals in the string "b/**/a".
71: Macro formal parameters are recognized in '#define' bodies even inside
72: character constants and quoted strings. The output from
73: #define foo(a) '\a'
74: foo(bar)
75: is the seven characters " '\\bar'". Macro names are not recognized
76: inside character constants or quoted strings during the regular scan.
77: Thus
78: #define foo bar
79: printf("foo");
80: does not expand 'foo' in the second line, because it is inside
81: a quoted string which is not part of a '#define' macro definition.
82: Macros are not expanded while processing a '#define' or '#undef'.
83: Thus
84: #define foo bletch
85: #define bar foo
86: #undef foo
87: bar
88: produces "foo". The token appearing immediately after a
89: '#ifdef' or '#ifndef' is not expanded (of course!).
90: Macros are not expanded during the scan which determines the actual
91: parameters to another macro call. Thus
92: #define foo(a,b)b a
93: #define bar hi
94: foo(bar,
95: #define bar bye
96: )
97: produces " bye" (and warns about the redefinition of 'bar').
98:
99: There are some differences between the new and the old preprocessor.
100: Bugs fixed:
101: "1.e4" is recognized as a floating-point number, rather than as an
102: opportunity to expand the possible macro name "e4".
103: Any kind and amount of white space (space, tab, linefeed, vertical tab,
104: formfeed, carriage return) is allowed between a macro name and
105: the left parenthesis which introduces its actual parameters.
106: The comma operator is legal in preprocessor '#if' statements.
107: Macros with parameters are legal in preprocessor '#if' statements.
108: Single-character character constants are legal in preprocessor '#if' statements.
109: Linefeeds are put out in the proper place when a multiline comment
110: is not passed through to the output.
111: The following example expands to "# # #" :
112: #define foo #
113: foo foo foo
114: If the -R flag is not specified then the invocation of some recursive
115: macros is trapped and the recursion forcibly terminated with an
116: error message. The recursions that are trapped are the ones
117: in which the nesting level is non-decreasing from some point on.
118: In particular,
119: #define a a
120: a
121: will be detected. (Use "#undef a" if that is what you want.)
122: The recursion
123: #define a c b
124: #define b c a
125: #define c foo
126: a
127: will not be detected because the nesting level decreases after
128: each expansion of "c".
129: The -R flag specifically allows recursive macros and recursion will
130: be strictly obeyed (to the extent that space is available).
131: Assuming that -R is specified:
132: #define a a
133: a
134: causes an infinite loop with very little output. The tail recursion
135: #define a <b
136: #define b >a
137: a
138: causes the string "<>" to be output infinitely many times. The
139: non-tail recursion
140: #define a b>
141: #define b a<
142: a
143: complains "too much pushback", dumps the pushback, and continues
144: (again, infinitely).
145:
146: Stylistic choice:
147: Nothing (not even linefeeds) is output while a false '#if', '#ifdef',
148: or '#ifndef' is in effect. Thus when all conditions become true
149: a line of the form "# 12345 \"foo.c\"" is output (unless -P).
150: Error and warning messages always appear on standard error (file
151: descriptor 2).
152: Mismatch between the number of formals and actuals in a macro call
153: produces only a warning, and not an error. Excess actuals
154: are ignored; missing actuals are turned into null strings.
155:
156: Incompatibility:
157: The virgule '/' in "a=/*b" is interpreted as the first character of
158: the pair "/*" which introduces a comment, rather than as the
159: second character of the divide-and-replace operator "=/".
160: This incompatibility reflects the recent change in the C language
161: which made "a/=*b" the legal way to write such a statement
162: if the meaning "a=a/ *b" is intended.
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