YACC(1) User Commands YACC(1)

NAME

yacc - yet another compiler-compiler

SYNOPSIS

yacc [-dltVv] [-b file_prefix] [-Q [y | n]]
[-P parser] [-p sym_prefix] file

DESCRIPTION

The yacc command converts a context-free grammar into a set of tables
for a simple automaton that executes an LALR(1) parsing algorithm.
The grammar can be ambiguous. Specified precedence rules are used to
break ambiguities.


The output file, y.tab.c, must be compiled by the C compiler to
produce a function yyparse(). This program must be loaded with the
lexical analyzer program, yylex(), as well as main() and yyerror(),
an error handling routine. These routines must be supplied by the
user. The lex(1) command is useful for creating lexical analyzers
usable by yacc.

OPTIONS

The following options are supported:

-b file_prefix
Uses file_prefix instead of y as the prefix for all
output files. The code file y.tab.c, the header
file y.tab.h (created when -d is specified), and
the description file y.output (created when -v is
specified), is changed to file_prefix.tab.c,
file_prefix.tab.h, and file_prefix.output,
respectively.


-d
Generates the file y.tab.h with the #define
statements that associate the yacc user-assigned
"token codes" with the user-declared "token names".
This association allows source files other than
y.tab.c to access the token codes.


-l
Specifies that the code produced in y.tab.c does
not contain any #line constructs. This option
should only be used after the grammar and the
associated actions are fully debugged.


-p sym_prefix
Uses sym_prefix instead of yy as the prefix for all
external names produced by yacc. The names affected
include the functions yyparse(), yylex() and
yyerror(), and the variables yylval, yychar and
yydebug. (In the remainder of this section, the six
symbols cited are referenced using their default
names only as a notational convenience.) Local
names can also be affected by the -p option.
However, the -p option does not affect #define
symbols generated by yacc.


-P parser
Allows you to specify the parser of your choice
instead of /usr/share/lib/ccs/yaccpar. For example,
you can specify:

example% yacc -P ~/myparser parser.y


-Q[y|n]
The -Qy option puts the version stamping
information in y.tab.c. This allows you to know
what version of yacc built the file. The -Qn option
(the default) writes no version information.


-t
Compiles runtime debugging code by default. Runtime
debugging code is always generated in y.tab.c under
conditional compilation control. By default, this
code is not included when y.tab.c is compiled.
Whether or not the -t option is used, the runtime
debugging code is under the control of YYDEBUG , a
preprocessor symbol. If YYDEBUG has a non-zero
value, then the debugging code is included. If its
value is 0, then the code is not included. The size
and execution time of a program produced without
the runtime debugging code is smaller and slightly
faster.


-v
Prepares the file y.output, which contains a
description of the parsing tables and a report on
conflicts generated by ambiguities in the grammar.


-V
Prints on the standard error output the version
information for yacc.

OPERANDS

The following operand is required:

file
A path name of a file containing instructions for which a
parser is to be created.

EXAMPLES

Example 1: Accessing the yacc Library

Access to the yacc library is obtained with library search operands
to cc. To use the yacc library main:


example% cc y.tab.c -ly


Both the lex library and the yacc library contain main. To access the
yacc main:


example% cc y.tab.c lex.yy.c -ly -ll


This ensures that the yacc library is searched first, so that its
main is used.


The historical yacc libraries have contained two simple functions
that are normally coded by the application programmer. These library
functions are similar to the following code:


#include <locale.h>
int main(void)
{
extern int yyparse();

setlocale(LC_ALL, "");

/* If the following parser is one created by lex, the
application must be careful to ensure that LC_CTYPE
and LC_COLLATE are set to the POSIX locale. */
(void) yyparse();
return (0);
}

#include <stdio.h>

int yyerror(const char *msg)
{
(void) fprintf(stderr, "%s\n", msg);
return (0);
}

ENVIRONMENT VARIABLES

See environ(7) for descriptions of the following environment
variables that affect the execution of yacc: LANG, LC_ALL, LC_CTYPE,
LC_MESSAGES, and NLSPATH.


yacc can handle characters from EUC primary and supplementary
codesets as one-token symbols. EUC codes can only be single character
quoted terminal symbols. yacc expects yylex() to return a wide
character (wchar_t) value for these one-token symbols.

EXIT STATUS

The following exit values are returned:

0
Successful completion.


>0
An error occurred.

FILES

y.output
state transitions of the generated parser


y.tab.c
source code of the generated parser


y.tab.h
header file for the generated parser


yacc.acts
temporary file


yacc.debug
temporary file


yacc.tmp
temporary file


yaccpar
parser prototype for C programs

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+

SEE ALSO

lex(1), attributes(7), environ(7), standards(7)

DIAGNOSTICS

The number of reduce-reduce and shift-reduce conflicts is reported on
the standard error output. A more detailed report is found in the
y.output file. Similarly, if some rules are not reachable from the
start symbol, this instance is also reported.

NOTES

Because file names are fixed, at most one yacc process can be active
in a given directory at a given time.


Users are encouraged to avoid using $ as part of any identifier name.

August 24, 2009 YACC(1)