Bison Verbose Syntax Error
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An action in the grammar can also explicitly proclaim an error, using the macro YYERROR (see Special Features for Use in Actions). bison syntax error unexpected identifier The Bison parser expects to report the error by calling an error
Bison Syntax Error Unexpected $end
reporting function named yyerror, which you must supply. It is called by yyparse whenever a syntax error bison yyerror is found, and it receives one argument. For a syntax error, the string is normally "syntaxerror". If you invoke ‘%define parse.error verbose’ in the Bison declarations section (see The
Yyerror Verbose
Bison Declarations Section), then Bison provides a more verbose and specific error message string instead of just plain "syntaxerror". However, that message sometimes contains incorrect information if LAC is not enabled (see LAC). The parser can detect one other kind of error: memory exhaustion. This can happen when the input contains constructions that are very deeply nested. bison error handling It isn’t likely you will encounter this, since the Bison parser normally extends its stack automatically up to a very large limit. But if memory is exhausted, yyparse calls yyerror in the usual fashion, except that the argument string is "memoryexhausted". In some cases diagnostics like "syntaxerror" are translated automatically from English to some other language before they are passed to yyerror. See Internationalization. The following definition suffices in simple programs: void yyerror (char const *s) { fprintf (stderr, "%s\n", s); } After yyerror returns to yyparse, the latter will attempt error recovery if you have written suitable error recovery grammar rules (see Error Recovery). If recovery is impossible, yyparse will immediately return 1. Obviously, in location tracking pure parsers, yyerror should have an access to the current location. With %define api.pure, this is indeed the case for the GLR parsers, but not for the Yacc parser, for historical reasons, and this is the why %define api.pure full should be prefered over %define api.pure. When %locations %define api.pure full is u
parse error whenever it reads a token which cannot satisfy any syntax rule. An action in the
Bison Syntax Error
grammar can also explicitly proclaim an error, using the macro YYERROR (see section
%define Parse.error Verbose
Special Features for Use in Actions). The Bison parser expects to report the error by calling an error reporting function bison error token named yyerror, which you must supply. It is called by yyparse whenever a syntax error is found, and it receives one argument. For a syntax error, the string is normally "syntax error". If https://www.gnu.org/s/bison/manual/html_node/Error-Reporting.html you invoke the directive %error-verbose in the Bison declarations section (see section The Bison Declarations Section), then Bison provides a more verbose and specific error message string instead of just plain "syntax error". The parser can detect one other kind of error: stack overflow. This happens when the input contains constructions that are very deeply nested. It isn't likely you will encounter this, since the Bison http://www.delorie.com/gnu/docs/bison/bison_76.html parser extends its stack automatically up to a very large limit. But if overflow happens, yyparse calls yyerror in the usual fashion, except that the argument string is "parser stack overflow". The following definition suffices in simple programs: void yyerror (char const *s) { fprintf (stderr, "%s\n", s); } After yyerror returns to yyparse, the latter will attempt error recovery if you have written suitable error recovery grammar rules (see section 6. Error Recovery). If recovery is impossible, yyparse will immediately return 1. Obviously, in location tracking pure parsers, yyerror should have an access to the current location. This is indeed the case for the GLR parsers, but not for the Yacc parser, for historical reasons. I.e., if `%locations %pure-parser' is passed then the prototypes for yyerror are: void yyerror (char const *msg); /* Yacc parsers. */ void yyerror (YYLTYPE *locp, char const *msg); /* GLR parsers. */ The prototypes are only indications of how the code produced by Bison uses yyerror. Bison-generated code always ignores the returned value, so yyerror can return any type, including void. Also, yyerror can be a variadic function; that is why the message is always passed last. Traditionally yyerror return
Linux or Unix, this useful book explains how to use flex and bison to solve your problems quickly. flex & bison is the long-awaited sequel to the classic O'Reilly http://www.oreilly.com/linux/excerpts/9780596155971/error-reporting-recovery.html book, lex & yacc. In the nearly two decades since the original book was published, http://dinosaur.compilertools.net/bison/bison_13.html the flex and bison utilities have proven to be more reliable and more powerful than the original Unix tools. flex & bison covers the same core functionality vital to Linux and Unix program development, along with several important new topics. You'll find revised tutorials for novices and references for advanced users, as well as an explanation of each syntax error utility's basic usage and simple, standalone applications you can create with them. With flex & bison, you'll discover the wide range of uses these flexible tools offer. The previous chapters discussed techniques for finding errors within bison grammars. In this chapter, we turn our attention to the other side of error detection--how the parser and lexical analyzer detect errors. This chapter presents some techniques to incorporate error detection and reporting into a bison syntax error parser. We'll make a modified version of the SQL parser from Parsing SQL that demonstrates them.Bison provides the error token and the yyerror() routine, which are typically sufficient for early versions of a tool. However, as any program begins to mature, especially a programming tool, it becomes important to provide better error recovery, which allows for detection of errors in later portions of the file, and to provide better error reporting. Error ReportingError reporting should give as much detail about the error as possible. The default bison error declares only that it found a syntax error and stops parsing. In our examples, we used yylineno to report the line number. This provides the location of the error but does not report any other errors within the file or where in the specified line the error occurs. The bison locations feature, described later in this chapter, is an easy way to pinpoint the location of an error, down to the exact line and character numbers. In our example, we print out the locations, but precise location information would also allow a visual interface to highlight the relevant text.It is often useful to categorize the possible errors, perhaps building an array of error types and defining symbolic constants to identify the errors. For example, in many languages a
halting the process. In effect, a sentence containing an error may be recognized as valid. On a parse error, the token error becomes the current look-ahead token. Actions corresponding to error are then executed, and the look-ahead token is reset to the token that originally caused the violation. See section Error Recovery. YYABORT Macro to pretend that an unrecoverable syntax error has occurred, by making yyparse return 1 immediately. The error reporting function yyerror is not called. See section The Parser Function yyparse. YYACCEPT Macro to pretend that a complete utterance of the language has been read, by making yyparse return 0 immediately. See section The Parser Function yyparse. YYBACKUP Macro to discard a value from the parser stack and fake a look-ahead token. See section Special Features for Use in Actions. YYERROR Macro to pretend that a syntax error has just been detected: call yyerror and then perform normal error recovery if possible (see section Error Recovery), or (if recovery is impossible) make yyparse return 1. See section Error Recovery. YYERROR_VERBOSE Macro that you define with #define in the Bison declarations section to request verbose, specific error message strings when yyerror is called. YYINITDEPTH Macro for specifying the initial size of the parser stack. See section Stack Overflow, and How to Avoid It. YYLEX_PARAM Macro for specifying an extra argument (or list of extra arguments) for yyparse to pass to yylex. See section Calling Conventions for Pure Parsers. YYLTYPE Macro for the data type of yylloc; a structure with four members. See section Textual Positions of Tokens. yyltype Default value for YYLTYPE. YYMAXDEPTH Macro for specifying the maximum size of the parser stack. See section Stack Overflow, and How to Avoid It. YYPARSE_PARAM Macro for specifying the name of a parameter that yyparse should accept. See section Calling Conventions for Pure Parsers. YYRECOVERING Macro whose value indicates whether the parser is recovering from a syntax error. See section Special Features for Use in Actions. YYSTYPE Macro for the data type of semantic values; int by default. See section Data Types of Semantic Values. yychar External integer variable that contains the integer value of the current look-ahead token. (In a pure parser, it is a loca