bt_macros(3) accessing and manipulating the btparse macro table

SYNOPSIS


void bt_add_macro_value (AST * assignment,
btshort options);
void bt_add_macro_text (char * macro,
char * text,
char * filename,
int line);
void bt_delete_macro (char * macro);
void bt_delete_all_macros (void);
int bt_macro_length (char *macro);
char * bt_macro_text (char * macro,
char * filename,
int line);

DESCRIPTION

btparse maintains a single table of all macros (abbreviations) encountered while parsing BibTeX entries. It updates this table whenever it encounters a ``macro definition'' (@string) entry, and refers to it whenever a macro is used in an entry and needs to be expanded. (Macros are not necessarily expanded on input, although this is the default. See bt_postprocess.) Macro definitions are only cleared when btparse's global cleanup function, "bt_cleanup()", is called. Thus, unless you explicitly call "bt_delete_macro()" or "bt_delete_all_macros()", macro definitions persist for as long as you use the library---usually, the lifetime of your process.

FUNCTIONS

You can use the following functions to add macros, delete them, and query their values---thus interfering with btparse's normal operation on the fly.
bt_add_macro_text ()
   void bt_add_macro_text (char * macro,
                           char * text,
                           char * filename,
                           int    line);

Defines a new macro, or redefines an old one. "macro" is the name of the macro, and "text" is the text it should expand to. "filename" and "line" are just used to generate any warnings about the macro definition; if they don't apply, specify "NULL" for "filename" and 0 for "line". The only such warning occurs when you redefine an old macro: its value is overridden, and "bt_add_macro_text()" issues a warning saying so.

For instance, when parsing this macro definition entry: 

   @string{fubar = "Fouled Up Beyond All Recognition"}

the library (in particular, the post-processing code called after an entry is successfully parsed) will ultimately do this: 

   bt_add_macro_text ("fubar", "Fouled Up Beyond All Recognition",
                      filename, line);

This in turn will cause the macro "fubar" to be expanded appropriately whenever the post-processing code sees it in any future entries.

bt_add_macro_value ()
   void bt_add_macro_value (AST *  assignment,
                            btshort options);

This function is mainly for internal use by the library, but it's available to you if you ever find yourself with a little bit of AST representing a macro definition, and you want to set the macro yourself (rather than letting the library's post-processing code take care of it for you). "assignment" must be an AST node as returned by "bt_next_field()". Unlike most other btparse functions that take an "options" argument, "options" here tells how the value in "assignment" was post-processed. This is needed because macro values have to be processed in a special way to be valid in future expansions; if this one wasn't processed like that, "bt_add_macro_value()" will do it for you. If you don't know how the value was post-processed, just supply 0 for "options"---that's guaranteed to describe something different from ``the right way'' for macros, so the post-processing will be done correctly.

The processing done to macro values is mainly to ensure that we can get away with storing just a string in the macro table: macros invoked by the macro are themselves expanded, and all sub-strings are concatenated. For instance, if btparse parses these entries: 

   @string{and = " and "}
   @string{jim_n_bob = "James Smith" # and # "Bob Jones"}

then the value stored for "jim_n_bob" should obviously be the string "James Smith and Bob Jones". To ensure this, btparse has to process the value of "and" differently from most BibTeX strings: in particular, whitespace is not collapsed before the string is stored. That way, the correct value, " and ", is interpolated into the value of "jim_n_bob". Thus, all macro values have sub-macros expanded and strings concatenated before they are stored, but whitespace is not collapsed until the macro is used in a regular entry.

This function calls "bt_add_macro_text()", so the same proviso about redefining old macros applies---a warning will be issued, and the old value lost.

bt_delete_macro ()
   void bt_delete_macro (char * macro);

Deletes a macro from the macro table. If "macro" isn't defined, takes no action.

bt_delete_all_macros ()
   void bt_delete_all_macros (void);

Deletes all macros from the macro table.

bt_macro_length ()
   int bt_macro_length (char *macro);

Returns the length of a macro's expansion text. If the macro is undefined, returns 0; no warning is issued.

bt_macro_text ()
   char * bt_macro_text (char * macro,
                         char * filename,
                         int line);

Returns the expansion text of a macro. If the macro is not defined, issues a warning and returns "NULL". "filename" and "line" are used for generating this warning; if they don't apply (i.e. you're not expanding the macro as a result of finding it in some file), supply "NULL" for "filename" and 0 for "line".

AUTHOR

Greg Ward <[email protected]>

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