traditional (K&R-style) C macro
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 are:
- Macro arguments are expanded within quoted strings. There is no stringize operator.
- There is no token pasting operator; tokens can be concatenated by placing comments between them. This process is also not limited to valid C language tokens.
- 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,
tradcppdoes 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,
tradcppdoes 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
tradcppdoes 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
-Wno-alldisables 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.
-Mbut skip system headers. Not implemented.
-Mbut write the dependency information to a file named after the input file with extension .d and preprocess normally to standard output. Not implemented.
-MMbut skip system headers. Not implemented.
- Send dependency output to the named file instead of the default location. Not implemented.
- 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
-MTexcept that any make(1) metacharacters 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.
More Include Path Options
- Add the specified path to the “afterwards” include path.
This path is searched after all directories specified with
-Iand the standard system directories. Directories on this path are treated as containing system include files.
- Read in file prior to reading the main input file, and preprocess it, but throw away the output and retain only the macro definitions.
- 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
__FILE__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
-iprefixand add this directory as if it were specified with
-iwithprefixbut adds the result as if it were specified with
- Write a trace of actions and operations to file as
the input is processed. Meant for debugging problems in complex
substitution schemes fed to
tradcpp, such as those used by imake.
- 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. Not implemented.
- Dump all macro definitions instead of the normal preprocessing output. Not implemented.
-dDbut emits only macro names and not the expansions. Not implemented.
- Output a trace of the include tree as it gets processed. Not implemented.
- Retain comments in output. Same as
-C, accepted for compatibility with gcc(1).
- 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.
tradcppto 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:
cc(1), cpp(1), make(1)
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.