traditional (K&R-style) C macro preprocessor
tradcpp command provides a traditional
K&R-style C macro preprocessor. It is intended to be suitable for
historical Unix uses of the preprocessor, such as
imake, particularly those that
depend on preservation of whitespace.
The chief ways in which traditional cpp differs from Standard C
- Macro arguments are expanded within quoted strings. There is no stringize
- There is no token pasting operator; tokens can be concatenated by placing
comments between them. This process is also not limited to valid C
- Whitespace is preserved, and in particular tabs are not expanded into
spaces. Furthermore, additional whitespace is not injected.
tradcpp has many options, many of which
are defined for compatibility with
gcc(1) or other compilers. Many
of the options are not yet implemented.
- Retain comments in output.
- Provide a definition for the named macro. If no expansion is provided, the
value “1” is used. Note that like many Unix compilers,
tradcpp does not accept a space between the
“D” and the macro name.
- Add the specified path to the main list of include directories. Note that
like many Unix compilers,
tradcpp does not accept
a space between the “I” and the directory name.
- Do not search the standard system include directories.
- Suppress line number information in the output. Currently line number
information is not generated at all and this option has no effect.
- Remove any existing definition for the named macro. Note that like many
tradcpp does not accept a space
between the “U” and the macro name.
- Remove all predefined macros.
Warning options can be disabled or enabled by inserting, or not,
the string “no-” between the “W” and the warning
name. Herein the “
-Wno-” form is shown
for options that are enabled by default.
- Turn on all warnings. The option
only the warnings that are disabled by default.
- Turn off all warnings.
- Make warnings into fatal errors.
- Warn about nested comments.
- Don't warn about symbols attached to #endif directives. (The warning is
currently not implemented.)
- Warn about undefined symbols appearing in #if and #elif expressions.
- Warn about macros that are defined and never used. Not implemented.
- Generate dependency information for
make(1) on the standard
output, instead of preprocessing. Not implemented.
-M but skip system headers. Not
-M but write the dependency information to a
file named after the input file with extension .d
and preprocess normally to standard output. Not implemented.
-MM but skip system headers. Not
- Send dependency output to the named file instead of the default location.
- When generating dependency information, assume that missing files are
generated instead of failing. Not implemented.
- Issue dummy rules for all include files. This prevents
make(1) from choking if an
include file is removed. Not implemented.
- Same as
-MT except that any
appearing in the target are escaped.
- Set the name of the make(1)
target appearing in the generated dependency information. The default is
the name of the input file with its suffix replaced with the suffix for
object files, normally .o.
- Add the specified path to the “afterwards” include path.
This path is searched after all directories specified with
-I and the standard system directories.
Directories on this path are treated as containing system include
- Read in file prior to reading the main input file,
and preprocess it, but throw away the output and retain only the macro
- Read in and preprocess file prior to reading the
main input file.
- Set the path prefix used with the
- Add path to the list of directories searched for
include directives written with quotes. This list is not searched for
include directives written with angle brackets.
- Substitute replacement for
string in the
built-in macro. Not supported.
- Use path as the “system root”, that
is, the directory under which the standard system paths are found.
- Add path to the list of system include directories.
This list is searched after the list given with I.
Files found on this path are treated as system headers.
- Splice dir onto the prefix given with
-iprefix and add this directory as if it were
-iwithprefix but adds the result as if it
were specified with
- Dump all macro definitions, except for the predefined macros, after the
normal preprocessing output. Not implemented.
- Dump all include directives along with the normal preprocessing output.
- Dump all macro definitions instead of the normal preprocessing output. Not
-dD but emits only macro names and not the
expansions. Not implemented.
- Output a trace of the include tree as it gets processed. Not
- Retain comments in output. Same as
for compatibility with
- Enable (or disable, respectively) the use of the dollar sign in
identifiers. Not implemented.
- Set the tab width to the specified value, for reporting column positions
in diagnostics. The default is 8. Not implemented.
tradcpp to conform to the named standard. The
default, and the only supported value, is “krc”.
- This option is accepted for compatibility with
gcc(1) and ignored.
- Adjust the preprocessor for the given language. The only values accepted
for lang are “assembler-with-cpp” and
“c”, neither of which have any effect on the behavior of
The default list of directories searched for include files is:
None. The whole point of a traditional cpp is that it reflects
practices in pre-standardization implementations of C. Some information is
available from the first edition of Kernighan and Ritchie. Much of the rest
of the behavior is based on lore, pragmatism, material encountered in the
wild, and comparison to other implementations.
The original version of
written one evening in late 2010. This version had some problems and was put
aside. The first working version was released in June 2013.