cproto - Man Page

generate C function prototypes and convert function definitions


cproto [ option ... ] [ file ... ]


Cproto generates function prototypes for functions defined in the specified C source files to the standard output. The function definitions may be in the old style or ANSI C style. Optionally, cproto also outputs declarations for variables defined in the files. If no file argument is given, cproto reads its input from the standard input.

By giving a command line option, cproto will also convert function definitions in the specified files from the old style to the ANSI C style. The original source files along with files specified by

#include "file"

directives appearing in the source code will be overwritten with the converted code. If no file names are given on the command line, then the program reads the source code from the standard input and outputs the converted source to the standard output.

If any comments appear in the parameter declarations for a function definition, such as in the example,

main (argc, argv)
int argc;       /* number of arguments */
char *argv[];   /* arguments */

then the converted function definition will have the form

main (
    int argc,       /* number of arguments */
    char *argv[]   /* arguments */

Otherwise, the converted function definition will look like

main (int argc, char *argv[])

Cproto can optionally convert function definitions from the ANSI style to the old style. In this mode, the program also converts function declarators and prototypes that appear outside function bodies. This is not a complete ANSI C to old C conversion. The program does not change anything within function bodies.

Cproto can optionally generate source in lint-library format. This is useful in environments where the lint utility is used to supplement prototype checking of your program.



Output the keyword extern in front of every generated prototype or declaration that has global scope.

-f n

Set the style of generated function prototypes where n is a number from 0 to 3. For example, consider the function definition

main (argc, argv)
int argc;
char *argv[];

If the value is 0, then no prototypes are generated. When set to 1, the output is:

int main(/*int argc, char *argv[]*/);

For a value of 2, the output has the form:

int main(int /*argc*/, char */*argv*/[]);

The default value is 3. It produces the full function prototype:

int main(int argc, char *argv[]);

Generate text for a lint-library (overrides the “-f” option). The output includes the comment


Special comments LINT_EXTERN and LINT_PREPRO (a la “VARARGS”) respectively turn on the “-x” option and copy comment-text to the output (for preprocessing in lint). Use the comment


to include externs defined in the first level of include-files. Use the comment


to cause cproto to put “#undef” directives before each lint library declaration (i.e., to avoid conflicts with macros that happen to have to have the same name as the functions, thus causing syntax errors).

Note that these special comments are not supported under VAX/VMS, since there is no equivalent for the “-C” option of cpp with VAX-C.


The parameter comments in the prototypes generated by the -f1 and -f2 options are omitted by default. Use this option to enable the output of these comments.


Put a macro around the parameter list of every generated prototype. For example:

int main P_((int argc, char *argv[]));
-M name

Set the name of the macro used to surround prototype parameter lists when option -m is selected. The default is “P_”.


Rather than filling in “void” for functions without parameters, use a comment “/*empty*/”.

-N name

Rather than filling in “void” for functions without parameters, use the given name.


Omit the definition of the prototype macro used by the -m option.

-o file

Specify the name of the output file (default: standard output).

-O file

Specify the name of the error file (default: standard error).


Disable promotion of formal parameters in old style function definitions. By default, parameters of type char or short in old style function definitions are promoted to type int in the function prototype or converted ANSI C function definition. Parameters of type float get promoted to double as well.


Do not output any error messages when the program cannot read the file specified in an #include directive.


By default, cproto only generates declarations for functions and variables having global scope. This option will output static declarations as well.


Output only static declarations.


By default, cproto only generates declarations for functions and variables having global scope. This option will output inline declarations as well.


Copy type definitions from each file. (Definitions in included-files are copied, unlike the “-l” option).


Also output declarations for variables defined in the source.


This option causes procedures and variables which are declared “extern” to be included in the output.

-X level

This option limits the include-file level from which declarations are extracted by examining the preprocessor output.


Convert function definitions from the old style to the ANSI C style.


Convert function definitions from the ANSI C style to the traditional style.


Rewrite function definition heads to include both old style and new style declarations separated by a conditional compilation directive. For example, the program can generate this function definition:

#ifdef ANSI_FUNC

main (int argc, char *argv[])

main (argc, argv)
int argc;
char *argv[]
-B directive

Set the conditional compilation directive to output at the beginning of function definitions generated by the -b option. The default is

#ifdef ANSI_FUNC
-P template
-F template
-C template

Set the output format for generated prototypes, function definitions, and function definitions with parameter comments respectively. The format is specified by a template in the form

" int f ( a, b )"

but you may replace each space in this string with any number of whitespace characters. For example, the option

-F"int f(\n\ta,\n\tb\n\t)"

will produce

int main(
        int argc,
        char *argv[]
-D name[=value]

This option is passed through to the preprocessor and is used to define  symbols for use with conditionals such as #ifdef.

-U name

This option is passed through to the preprocessor and is used to remove any definitions of this symbol.

-I directory

This option is passed through to the preprocessor and is used to specify a directory to search for files that are referenced with #include.

-E cpp

Pipe the input files through the specified C preprocessor command when generating prototypes. By default, the program uses /lib/cpp.

-E 0

Do not run the C preprocessor.


Print version information.


The environment variable CPROTO is scanned for a list of options in the same format as the command line options. Options given on the command line override any corresponding environment option.


If an un-tagged struct, union or enum declaration appears in a generated function prototype or converted function definition, the content of the declaration between the braces is empty.

The program does not pipe the source files through the C preprocessor when it is converting function definitions. Instead, it tries to handle preprocessor directives and macros itself and can be confused by tricky macro expansions. The conversion also discards some comments in the function definition head.

The -v option does not generate declarations for variables defined with the extern specifier. This doesn't strictly conform to the C language standard but this rule was implemented because include files commonly declare variables this way.

When the program encounters an error, it usually outputs the not very descriptive message “syntax error”. (Your configuration may allow the extended error reporting in yyerror.c).

Options that take string arguments only interpret the following character escape sequences:


VARARGS comments don't get passed through on systems whose C preprocessors don't support this (e.g., VAX/VMS, MS-DOS).


Chin Huang

Thomas E. Dickey
modifications to support lint library, type-copying, and port to VAX/VMS.

See Also

cc(1), cpp(1)


2023-02-05 Version 4.7v USER COMMANDS