Manual

Chapter 10: C++ Language Interface 103
10.1.4 C++ Parser Interface
The output files ‘output.hh’ and ‘output.cc’ declare and define the parser class in the
namespace yy. The class name defaults to parser, but may be changed using ‘%define
"parser_class_name" "name"’. The interface of this class is detailed below. It can be
extended using the %parse-param feature: its semantics is slightly changed since it describes
an additional member of the parser class, and an additional argument for its constructor.
semantic_value_type
location_value_type
The types for semantics value and locations.
[Type of parser]
[Type of parser]
parser (type1 arg1, ...)
[Method on parser]
Build a new parser object. There are no arguments by default, unless ‘%parse-param
{type1 arg1}’ was used.
int parse ()
[Method on parser]
Run the syntactic analysis, and return 0 on success, 1 otherwise.
std::ostream& debug_stream ()
[Method on parser]
void set_debug_stream (std::ostream& o )
[Method on parser]
Get or set the stream used for tracing the parsing. It defaults to std::cerr.
debug_level_type debug_level ()
[Method on parser]
void set_debug_level (debug level l )
[Method on parser]
Get or set the tracing level. Currently its value is either 0, no trace, or nonzero, full
tracing.
void error (const location type& l, const std::string& m ) [Method on parser]
The definition for this member function must be supplied by the user: the parser uses
it to report a parser error occurring at l, described by m.
10.1.5 C++ Scanner Interface
The parser invokes the scanner by calling yylex. Contrary to C parsers, C++ parsers are
always pure: there is no point in using the %pure-parser directive. Therefore the interface
is as follows.
int yylex (semantic value type& yylval, location type& [Method on parser]
yylloc, type1 arg1, ...)
Return the next token. Its type is the return value, its semantic value and location
being yylval and yylloc. Invocations of ‘%lex-param {type1 arg1}’ yield additional
arguments.
10.2 A Complete C++ Example
This section demonstrates the use of a C++ parser with a simple but complete example.
This example should be available on your system, ready to compile, in the directory ../bison/examples/calc++.
It focuses on the use of Bison, therefore the design of the various
C++ classes is very naive: no accessors, no encapsulation of members etc. We will use a
Lex scanner, and more precisely, a Flex scanner, to demonstrate the various interaction. A
hand written scanner is actually easier to interface with.