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util/cpp/cpp.6
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.TH
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.I cpp
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.SH NAME
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cpp \- C Pre-Processor
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.SH SYNOPSIS
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cpp [\-options] files
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.SH DESCRIPTION
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.I Cpp
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reads one or more files, expands macros and include
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files, and writes an input file for the C compiler.
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All output is to cpp.tmp (cpp.tmp.c on Unix).
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.br
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The following options are supported. On non-Unix systems,
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options may be given in either case.
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.IP -Ofile
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Output to this file, instead of the default.
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.IP -S
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Output to stdout, instead of the default.
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.IP -Idirectory
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Add this directory to the list of
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directories searched for #include "..." and #include <...>
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commands. Note that there is no space between the
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"-I" and the directory string. More than one -I command
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is permitted.
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.IP -L
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.I Cpp
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transmits line number information to
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the C compiler by outputting "#line <number>" records.
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If the -L option is given, this record will be transmitted
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as "#", allowing the output of
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.I cpp
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to be input to a compiler
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without an intervening preprocessor without error.
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.IP -Dname=value
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Define the name as if the programmer wrote
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.br
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.nf
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#define name value
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.fi
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.br
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at the start of the first file. If "=value" is not
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given, a value of "1" will be used.
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.br
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On non-unix systems, all alphabetic text will be forced
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to upper-case.
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.br
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.IP -Uname
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Undefine the name as if
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.br
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.nf
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#undef name
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.fi
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.br
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were given. On non-Unix systems, "name" will be forced to
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upper-case.
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The following names are always available unless undefined:
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.RS
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.IP __FILE__
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The input (or #include) file being compiled
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(as a quoted string).
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.IP __LINE__
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The line number being compiled.
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.IP __DATE__
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The date and time of compilation as
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a Unix ctime quoted string (the trailing newline is removed).
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.RE
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Thus,
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.br
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.nf
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printf("Bug at line %s,", __LINE__);
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printf(" source file %s", __FILE__);
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printf(" compiled on %s", __DATE__);
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.fi
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.IP
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-Xnumber
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Enable debugging code. If no value is
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given, a value of 1 will be used. (For maintenence of
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.I cpp
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only.)
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.SH "COMMENTS IN MACRO TEXT AND ARGUMENT CONCATENATION"
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.br
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Comments are removed from the input text. The comment
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characters serve as an invisible token delimiter. Thus,
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the macro
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.nf
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#define CAT(a, b) b/**/a
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int value = CAT(1, 2);
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.fi
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Will generate "int value = 21;".
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.br
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A better way of concatenating arguments is as follows:
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.nf
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#define I(x)x
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#define CAT(x,y)I(x)y
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int value = CAT(1, 2);
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.fi
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If the above macros are defined without extraneous
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spaces, they will be transportable to other implementations.
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.br
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.SH DIFFERENCES
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.br
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The following is a list of differences between this
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pre-processor and the Unix V7 preprocessor which was
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written by John Reiser. It is probably not complete.
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.IP o
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Macro formal parameters are recognized within
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quoted strings and character constants in macro definitions.
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For example,
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.nf
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#define foo(a) "Today is a"
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printf(foo(tuesday));
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.fi
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Would print "Today is tuesday".
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.br
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Recognition of formal parameters in macro replacement
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strings is not permitted by the Draft ANSI C Standard.
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It is permitted in this implementation if cpp was
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compiled with the STRING_FORMAL parameter set appropriately.
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.br
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Unlike Reiser's implementation, the '\e' "quote next character"
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does just that. I.e.
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.nf
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#define foo(a) "Today is \ea a"
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printf(foo(tuesday));
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.fi
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Would print "Today is a tuesday". Note that this may
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not be portable.
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.IP o
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Reiser's implementation removes "escaped" linefeeds
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(The two character sequence \e<LF>) within macros. This
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implementation preserves them. For example, a macro which
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generates control commands might be written
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.nf
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#define foo(a, b) \e
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#define a b \e
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.fi
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.nf
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foo(fubar, foobar)
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int fubar;
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.fi
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The above would generate "int foobar;" and a warning message.
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Reiser's scan is slightly different.
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.SH "ANSI C STANDARD"
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.I Cpp
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implements most of the ANSI draft standard.
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You should be aware of the following:
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.IP o
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In the draft standard, the \en (backslash-newline)
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character is "invisible" to all processing. In this implementation,
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it is invisible to strings, but acts a "whitespace" (token-delimiter)
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outside of strings. This considerably simplifies error
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message handling.
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.IP o
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The following extensions to C are processed by cpp:
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.nf
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.sp 1
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.ta 4 27
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#elif expression (#else #if)
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'\exNNN' (Hexadecimal constants)
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'\ea' (Ascii BELL)
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'\ev' (Ascii VT)
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#if defined NAME (1 if defined, 0 if not)
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#if defined (NAME) (1 if defined, 0 if not)
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unary + (gag me with a spoon)
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.fi
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.IP o
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The draft standard has extended C, adding a string
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concatenation operator, where
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.br
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.nf
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"foo" "bar"
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.fi
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.br
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is regarded as the single string "foobar". It is not clear
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from the draft standard whether this applies to pre-processing
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if macro formals are recognized in strings.
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.SH "ERROR MESSAGES"
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.br
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Many.
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.br
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.SH AUTHOR
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.br
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Martin Minow
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.br
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