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Manual Reference Pages  -  BTPARSE (1)

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btparse - C library for parsing and processing BibTeX data files



   #include <btparse.h>

   /* Basic library initialization / cleanup */
   void bt_initialize (void);
   void bt_free_ast (AST *ast);
   void bt_cleanup (void);

   /* Input / interface to parser */
   void   bt_set_stringopts (bt_metatype_t metatype, btshort options);
   AST * bt_parse_entry_s (char *    entry_text,
                           char *    filename,
                           int       line,
                           btshort    options,
                           boolean * status);
   AST * bt_parse_entry   (FILE *    infile,
                           char *    filename,
                           btshort    options,
                           boolean * status);
   AST * bt_parse_file    (char *    filename,
                           btshort    options,
                           boolean * overall_status);

   /* AST traversal/query */
   AST * bt_next_entry (AST * entry_list,
                        AST * prev_entry)
   AST * bt_next_field (AST *entry, AST *prev, char **name);
   AST * bt_next_value (AST *head,
                        AST *prev,
                        bt_nodetype_t *nodetype,
                        char **text);

   bt_metatype_t bt_entry_metatype (AST *entry);
   char *bt_entry_type (AST *entry);
   char *bt_entry_key (AST *entry);
   char *bt_get_text (AST *node);

   /* Splitting names and lists of names */
   bt_stringlist * bt_split_list (char *   string,
                                  char *   delim,
                                  char *   filename,
                                  int      line,
                                  char *   description);
   void bt_free_list (bt_stringlist *list);
   bt_name * bt_split_name (char *  name,
                            char *  filename,
                            int     line,
                            int     name_num);
   void bt_free_name (bt_name * name);

   /* Formatting names */
   bt_name_format * bt_create_name_format (char * parts, boolean abbrev_first);
   void bt_free_name_format (bt_name_format * format);
   void bt_set_format_text (bt_name_format * format,
                            bt_namepart part,
                            char * pre_part,
                            char * post_part,
                            char * pre_token,
                            char * post_token);
   void bt_set_format_options (bt_name_format * format,
                               bt_namepart part,
                               boolean abbrev,
                               bt_joinmethod join_tokens,
                               bt_joinmethod join_part);
   char * bt_format_name (bt_name * name, bt_name_format * format);

   /* Construct tree from TeX groups */
   bt_tex_tree * bt_build_tex_tree (char * string);
   void          bt_free_tex_tree (bt_tex_tree **top);
   void          bt_dump_tex_tree (bt_tex_tree *node, int depth, FILE *stream);
   char *        bt_flatten_tex_tree (bt_tex_tree *top);

   /* Miscellaneous string utilities */
   void bt_purify_string (char * string, btshort options);
   void bt_change_case (char transform, char * string, btshort options);


<B>btparseB> is a C library for parsing and processing BibTeX files. It provides a lexical scanner and LR parser (constructed by PCCTS), both of which are efficient and offer good error detection and recovery; a set of functions for traversing the AST (abstract syntax tree) generated by the parser; and utility functions for manipulating strings according to BibTeX conventions. (Note that nothing in the library assumes that you’re using BibTeX files for their original purpose of bibliographic data for scholarly publications; you could use the file format for any conceivable purpose that fits it. However, there is some code in the library that is really only appropriate for use with strings meant to be processed in the same way that BibTeX itself does. This is all entirely optional, though.)

Note that the interface provided by <B>btparseB>, while complete, is fairly low-level. If you have more sophisticated needs, you might be interested my Text::BibTeX module for Perl 5 (available on CPAN).


To understand this document and use <B>btparseB>, you should already be familiar with the BibTeX language---more specifically, the BibTeX data description language. (BibTeX being the complex beast that it is, one can conceive of the term applying to the program, the data language, the particular database structure described in the original BibTeX documentation, the .bst formatting language, and the set of conventions embodied in the standard styles included with the BibTeX distribution. In this document, I’ll stick to the first two meanings---the data language because that’s what <B>btparseB> deals with, and the program because it’s occasionally necessary to explain differences between my parser and BibTeX’s.)

In particular, you should have a good idea what’s going on in the following:

   @string{and = { and },
           joe = "Blow, Joe",
           john = "John Smith"}

         author = joe # and # john,
         title = {Our Little Book})

If this looks like something you want to parse, but don’t want to have to write your own parser for, you’ve come to the right place.

Before going much further, though, you’re going to have to learn some of the terminology I use for describing BibTeX data. Most of it’s the same as you’ll find in any BibTeX documentation, but it’s important to be sure that we’re talking about the same things here. So, some definitions:
top-level All text in a BibTeX file from the start of the file to the start of the first entry, and between entries thereafter.
name A string of letters, digits, and the following characters:

   ! $ & * + - . / : ; < > ? [ ] ^ _ ` |

A name is a catch-all used for entry types, entry keys, and field and macro names. For BibTeX compatibility, there are slightly different rules for these four entities; currently, the only such rule actually implemented is that field and macro names may not begin with a digit. Some names in the above example: string, and.

entry A chunk of text starting with an at sign (@) at top-level, followed by a name (the entry type), an entry delimiter ({ or (), and proceeding to the matching closing delimiter. Also, the data structure that results from parsing this chunk of text. There are two entries in the above example.
entry type The name that comes right after an @ at top-level. Examples from above: string, book.
entry metatype A classification of entry types that allows us to group one or more entry types under the same heading. With the standard BibTeX database structure, article, book, inbook, etc. all fall under the regular entry metatype. Other metatypes are macro definition (for string entries), preamble (for preamble) entries, and comment (comment entries). In fact, any entry whose type is not one of string, preamble, or comment is called a regular entry.
entry delimiters { and }, or ( and ): the pair of characters that (almost) mark the boundaries of an entry. Almost because the start of an entry is marked by an @, not by the entry open delimiter.
entry key (Or just key when it’s clear what we’re speaking of.) The name immediately following the entry open delimiter in a regular entry, which uniquely identifies the entry. Example from above: ourbook. Only regular entries have keys.
field A name to the left of an equals sign in a regular or macro-definition entry. In the latter context, might also be called a macro name. Examples from above: joe, author.
field list In a regular entry, everything between the entry delimiters except for the entry key. In a macro definition entry, everything between the entry delimiters (possibly also called a macro list).
compound value (Usually just value.) The text that follows an equals sign (=) in a regular or macro definition entry, up to a comma or the entry close delimiter; a list of one or more simple values joined by hash signs (#).
simple value A string, macro, or number.
string (Or, sometimes, quoted string.) A chunk of text between quotes (") or braces ({ and }). Braces must balance: {this is a {string} is not a BibTeX string, but {this is a {string}} is. ("this is a {string" is also illegal, mainly to avoid the possibility of generating bogus TeX code—which BibTeX will do in certain cases.)
macro A name that appears on the right-hand side of an equals sign (i.e. as one simple value in a compound value). Implies that this name was defined as a macro in an earlier macro definition entry, but this is only checked if <B>btparseB> is being asked to expand macros to their full definitions.
number An unquoted string of digits.
Working with <B>btparseB> generally consists of passing the library some BibTeX data (or a source for some BibTeX data, such as a filename or a file pointer), which it then lexically scans, parses, and constructs an abstract syntax tree (AST) from. It returns this AST to you, and you call other <B>btparseB> functions to traverse and query the tree.

The contents of AST nodes are the private domain of the library, and you shouldn’t go poking into them. This being C, though, there’s nothing to prevent you from doing so except good manners and the possibility that I might change the AST structure in future releases, breaking any badly-behaved code. Also, it’s not necessary to know the structural relationships between nodes in the AST---that’s taken care of by the query/traversal functions.

However, it’s useful to know some of the things that <B>btparseB> deposits in the AST and returns to you through those query/traversal functions. First off, each node has a node type, which records the syntactic element corresponding to each node. For instance, the entry

   @book{mybook, author = "Joe Blow", title = "My Little Book"}

is rooted by an entry node; under this would be found a key node (for the entry key), two field nodes (for the author and title fields); and associated with each field node would be a string node. The only time this concerns you is when you ask the library for a simple value; just looking at the text is not enough to distinguish quoted strings, numbers, and macro names, so <B>btparseB> returns the nodetype as well.

In addition to the nodetype, <B>btparseB> records the metatype of each entry node. This allows you (and the library) to distinguish, say, regular entries from comment entries. Not only do they have very different structures and must therefore be traversed differently by the library, but certain traversal functions make no sense on certain entry metatypes---thus it’s necessary for you to be able to make the distinction as well.

That said, everything you need to know to work with the AST is explained in bt_traversal.


<B>btparseB> defines several types required for the external interface. First, it trivially defines a boolean type (along with TRUE and FALSE macros). This might affect you when including the btparse.h header in your own code---since it’s not possible for the code to detect if there is already a boolean type defined, you might have to define the HAVE_BOOLEAN pre-processor token to deactivate btparse.h’s typedef of boolean.

Next, two enumeration types are defined: bt_metatype and bt_nodetype. Both of these are used extensively in the library itself, and are made available to users of the library because they can be found in nodes of the btparse AST (abstract syntax tree). (I.e., querying the AST can give you bt_metatype and bt_nodetype values, so the typedefs must be available to your code.)

    Entry metatype enum

bt_metatype_t has the following values:
which are determined by the entry type token. (@string entries have the BTE_MACRODEF metatype; @comment and @preamble correspond to BTE_COMMENT and BTE_PREAMBLE; and any other entry type has the BTE_REGULAR metatype.)

    AST nodetype enum

bt_nodetype has the following values:
Of these, you’ll only ever deal with the last three. They are returned when you query the AST for a simple value---just seeing the text isn’t enough to distinguish between a quoted string, a number, and a macro, so the AST nodetype is supplied along with the text.

    String processing option macros

Since BibTeX is essentially a system for glueing strings together in a wide variety of ways, the processing done to its strings is fairly important. Most of the string transformations are done outside of the lexer/parser; this reduces their complexity, and makes it easier to switch different transformations on and off. This switching is done with an options bitmap which can be specified on a per-entry-metatype basis. (That is, you can have one set of transformations done to the strings in all regular entries, another set done to the strings in all macro definition entries, and so on.) If you need finer control than that, it’s currently unavailable outside of the library (but it’s just a matter of making a couple functions available and documenting them---so bug me if you need this feature).

There are three basic macros for constructing this bitmap:
BTO_CONVERT Convert number values to strings. (The conversion is trivial, involving changing the type of the AST node representing the number from BTAST_NUMBER to BTAST_STRING. Number values are stored as strings of digits, just as they are in the input data.)
BTO_EXPAND Expand macro invocations to the full macro text.
BTO_PASTE Paste simple values together.
BTO_COLLAPSE Collapse whitespace according to the BibTeX rules.
For instance, supplying BTO_CONVERT | BTO_EXPAND as the string options bitmap for the BTE_REGULAR metatype means that all simple values in regular entries will be converted to strings: numbers will simply have their nodetype changed, and macros will be expanded. Nothing else will be done to the simple values, though---they will not be concatenated, nor will whitespace be collapsed. See the bt_set_stringopts() and bt_parse_*() functions in bt_input for more information on the various options for parsing; see bt_postprocess for details on the post-processing.


The following code is a skeletal example of using the <B>btparseB> library:

    #include <btparse.h>

    int main (void)
       bt_initialize ();

       /* process some data */

       bt_cleanup ();
       exit (0);

Please note the call to bt_initialize(); this is very important! Without it, the library may crash or fail mysteriously. You must call bt_initialize() before calling any other <B>btparseB> functions. bt_cleanup() just frees the memory allocated by bt_initialize(); if you are careful to call it before exiting, and bt_free_ast() on any abstract syntax trees generated by <B>btparseB> when you are done with them, then your program shouldn’t have any memory leaks. (Unless they’re due to your own code, of course!)


<B>btparseB> has several inherent limitations that are due to the lexical scanner and parser generated by PCCTS 1.x. In short, the scanner and parser are both heavily dependent on global variables, meaning that thread safety — or even the ability to have two files open and being parsed at the same time — is well-nigh impossible. This will not change until I get with the times and adopt ANTLR 2.0, the successor to PCCTS — presuming of course that it can generate more modular C scanners and parsers.

Another limitation that is due to PCCTS: entries with a large number of fields (more than about 90, if each field value is just a single string) will cause the parser to crash. This is unavoidable due to the parser using statically-allocated stacks for attributes and abstract-syntax tree nodes. I could increase the static allocation, but that would just decrease the likelihood of encountering the problem, not make it go away. Again, the chances of this changing as long as I’m using PCCTS 1.x are nil.

Apart from those inherent limitations, there are no known bugs in <B>btparseB>. Any segmentation faults or bus errors from the library should be considered bugs. They probably result from using the library incorrectly (eg. attempting to interleave the parsing of two files), but I do make an attempt to catch all such mistakes, and if I’ve missed any I’d like to know about it.

Any memory leaks from the library are also a concern; as long as you are conscientious about calling the cleanup functions (bt_free_ast() and bt_cleanup()), then the library shouldn’t leak.


To read and parse BibTeX data files, see bt_input.

To traverse the syntax tree that results, see bt_traversal.

To learn what is done to values in parsed entries, and how to customize that munging, see bt_postprocess.

To learn how <B>btparseB> deals with strings, see bt_strings (oops, I haven’t written this one yet!).

To manipulate and access the <B>btparseB> macro table, see bt_macros.

For splitting author names and lists the BibTeX way using <B>btparseB>, bt_split_names.

To put author names back together again, see bt_format_names.

Miscellaneous functions for processing strings the BibTeX way: bt_misc.

A semi-formal language definition is in bt_language.


Greg Ward <>


Copyright (c) 1996-97 by Gregory P. Ward.

This library is free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public License for more details.

You should have received a copy of the GNU Library General Public License along with this library; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


The btOOL home page, where you can get up-to-date information about <B>btparseB> (and download the latest version) is

You will also find the latest version of <B>Text::BibTeXB>, the Perl library that provides a high-level front-end to <B>btparseB>, there. <B>btparseB> is needed to build Text::BibTeX, and must be downloaded separately.

Both libraries are also available on CTAN (the Comprehensive TeX Archive Network, and CPAN (the Comprehensive Perl Archive Network, Look in biblio/bibtex/utils/btOOL/ on CTAN, and authors/Greg_Ward/ on CPAN. For example,

will both get you to the latest version of Text::BibTeX and <B>btparseB> — but of course, you should always access busy sites like CTAN and CPAN through a mirror.

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