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-
-
-
- Using the GEDCOM parser library
-
-
-
-
-
+Using the GEDCOM parser library
+
+
+
+
Using the GEDCOM parser library
-
-
+
+
Index
-
+
-
-
+
+
Overview
-
- The GEDCOM parser library is built as a callback-based parser (comparable
- to the SAX interface of XML). It comes with:
-
+
+ The GEDCOM parser library is built as a callback-based parser (comparable
+ to the SAX interface of XML). It comes with:
+
- - a library (
libgedcom.so), to be linked in the application
- program
- - a header file (
gedcom.h), to be used in the sources
- of the application program
- - a header file (
gedcom-tags.h) that is also installed,
-but that is automatically included via gedcom.h
-
-
+ - a library (
libgedcom.so), to be linked in the application
+ program
+ - a header file (
gedcom.h), to be used in the sources
+ of the application program
+ - a header file (
gedcom-tags.h) that is also installed,
+ but that is automatically included via gedcom.h
+
+
- Next to these, there is also a data directory in $PREFIX/share/gedcom-parse
- that contains some additional stuff, but which is not immediately important
- at first. I'll leave the description of the data directory for later.
-
- The very simplest call of the gedcom parser is simply the following piece
- of code (include of the gedcom header is assumed, as everywhere in this
-manual):
-
-int result;
- ...
- result = gedcom_parse_file("myfamily.ged");
-
- Although this will not provide much information, one thing it does is
-parse the entire file and return the result. The function returns 0
-on success and 1 on failure. No other information is available using
-this function only.
-
- The next sections will refine this to be able to have meaningful errors
- and the actual data that is in the file.
+ Next to these, there is also a data directory in $PREFIX/share/gedcom-parse
+ that contains some additional stuff, but which is not immediately
+important at first. I'll leave the description of the data directory
+for later.
+
+ The very simplest call of the gedcom parser is simply the following
+piece of code (include of the gedcom header is assumed, as everywhere in
+this manual):
-
+int result;
+ ...
+ result = gedcom_parse_file("myfamily.ged");
+
+ Although this will not provide much information, one thing it does
+is parse the entire file and return the result. The function returns
+0 on success and 1 on failure. No other information is available using
+ this function only.
+
+ The next sections will refine this to be able to have meaningful errors
+ and the actual data that is in the file.
+
+
Error handling
- Since this is a relatively simple topic, it is discussed before the actual
- callback mechanism, although it also uses a callback...
-
- The library can be used in several different circumstances, both terminal-based
- as GUI-based. Therefore, it leaves the actual display of the error
-message up to the application. For this, the application needs to register
-a callback before parsing the GEDCOM file, which will be called by the library
- on errors, warnings and messages.
-
- A typical piece of code would be:
-
+ Since this is a relatively simple topic, it is discussed before the
+actual callback mechanism, although it also uses a callback...
+
+ The library can be used in several different circumstances, both terminal-based
+ as GUI-based. Therefore, it leaves the actual display of the error
+ message up to the application. For this, the application needs to register
+ a callback before parsing the GEDCOM file, which will be called by the library
+ on errors, warnings and messages.
+
+ A typical piece of code would be:
+
void my_message_handler (Gedcom_msg_type type,
- char *msg)
- {
- ...
- }
- ...
- gedcom_set_message_handler(my_message_handler);
- ...
- result = gedcom_parse_file("myfamily.ged");
-
- In the above piece of code, my_message_handler is the callback
- that will be called for errors (type=ERROR), warnings (
- type=WARNING) and messages (type=MESSAGE). The
-callback must have the signature as in the example. For errors, the
- msg passed to the callback will have the format:
-
- Error on line <lineno>: <actual_message>
+ char *msg)
+ {
+ ...
+ }
+ ...
+ gedcom_set_message_handler(my_message_handler);
+ ...
+ result = gedcom_parse_file("myfamily.ged");
- Note that the entire string will be properly internationalized, and encoded
- in UTF-8 (see "Why UTF-8?" LINK TBD). Also, no newline
- is appended, so that the application program can use it in any way it wants.
- Warnings are similar, but use "Warning" instead of "Error". Messages
- are plain text, without any prefix.
-
- With this in place, the resulting code will already show errors and warnings
- produced by the parser, e.g. on the terminal if a simple printf
- is used in the message handler.
-
-
- Data callback mechanism
- The most important use of the parser is of course to get the data out
-of the GEDCOM file. As already mentioned, the parser uses a callback
-mechanism for that. In fact, the mechanism involves two levels.
-
- The primary level is that each of the sections in a GEDCOM file is notified
- to the application code via a "start element" callback and an "end element"
- callback (much like in a SAX interface for XML), i.e. when a line containing
- a certain tag is parsed, the "start element" callback is called for that
-tag, and when all its subordinate lines with their tags have been processed,
-the "end element" callback is called for the original tag. Since GEDCOM
- is hierarchical, this results in properly nested calls to appropriate "start
- element" and "end element" callbacks.
-
- However, it would be typical for a genealogy program to support only a
-subset of the GEDCOM standard, certainly a program that is still under development.
- Moreover, under GEDCOM it is allowed for an application to define its
- own tags, which will typically not be supported by another application.
- Still, in that case, data preservation is important; it would hardly
- be accepted that information that is not understood by a certain program
-is just removed.
-
- Therefore, the second level of callbacks involves a "default callback".
- An application needs to subscribe to callbacks for tags it does support,
- and need to provide a "default callback" which will be called for tags it
- doesn't support. The application can then choose to just store the
-information that comes via the default callback in plain textual format.
-
- After this introduction, let's see what the API looks like...
-
-
- Start and end callbacks
-
- Callbacks for records
-
- As a simple example, we will get some information from the header of a
-GEDCOM file. First, have a look at the following piece of code:
-
- Gedcom_ctxt my_header_start_cb (int level,
- Gedcom_val xref, char *tag, int parsed_tag)
- {
- printf("The header starts\n");
- return (Gedcom_ctxt)1;
- }
-
- void my_header_end_cb (Gedcom_ctxt self)
- {
- printf("The header ends, context is %d\n", self); /* context
- will print as "1" */
- }
-
- ...
- gedcom_subscribe_to_record(REC_HEAD, my_header_start_cb,
- my_header_end_cb);
- ...
- result = gedcom_parse_file("myfamily.ged");
+ In the above piece of code, my_message_handler is the callback
+ that will be called for errors (type=ERROR), warnings (type=WARNING) and messages (type=MESSAGE). The
+ callback must have the signature as in the example. For errors, the
+ msg passed to the callback will have the format:
+
+ Error on line <lineno>: <actual_message>
- Using the gedcom_subscribe_to_record function, the application
- requests to use the specified callbacks as start and end callback. The end
- callback is optional: you can pass NULL if you are not interested
- in the end callback. The identifiers to use as first argument to the
- function (here REC_HEAD) are described in the
- interface details.
+ Note that the entire string will be properly internationalized, and
+encoded in UTF-8 (see "Why UTF-8?" LINK TBD). Also,
+no newline is appended, so that the application program can use it in any
+way it wants. Warnings are similar, but use "Warning" instead of
+"Error". Messages are plain text, without any prefix.
+
+ With this in place, the resulting code will already show errors and
+warnings produced by the parser, e.g. on the terminal if a simple
+printf is used in the message handler.
+
+
+ Data callback mechanism
+ The most important use of the parser is of course to get the data out
+ of the GEDCOM file. As already mentioned, the parser uses a callback
+ mechanism for that. In fact, the mechanism involves two levels.
- From the name of the function it becomes clear that this function is specific
- to complete records. For the separate elements in records there is
-another function, which we'll see shortly. Again, the callbacks need
-to have the signatures as shown in the example.
+ The primary level is that each of the sections in a GEDCOM file is notified
+ to the application code via a "start element" callback and an "end element"
+ callback (much like in a SAX interface for XML), i.e. when a line containing
+ a certain tag is parsed, the "start element" callback is called for that
+ tag, and when all its subordinate lines with their tags have been processed,
+ the "end element" callback is called for the original tag. Since GEDCOM
+ is hierarchical, this results in properly nested calls to appropriate "start
+ element" and "end element" callbacks.
- The Gedcom_ctxt type that is used as a result of the start
- callback and as an argument to the end callback is vital for passing context
- necessary for the application. This type is meant to be opaque; in
-fact, it's a void pointer, so you can pass anything via it. The important
- thing to know is that the context that the application returns in the start
- callback will be passed in the end callback as an argument, and as we will
- see shortly, also to all the directly subordinate elements of the record.
-
-The tag is the GEDCOM tag in string format, the parsed_tag
- is an integer, for which symbolic values are defined as TAG_HEAD,
- TAG_SOUR, TAG_DATA, ... and USERTAG gedcom-tags.h that is installed, and included via
-gedcom.h (so no need to include gedcom-tags.h yourself).
+ However, it would be typical for a genealogy program to support only
+a subset of the GEDCOM standard, certainly a program that is still under
+development. Moreover, under GEDCOM it is allowed for an application
+to define its own tags, which will typically not be supported by another
+application. Still, in that case, data preservation is important;
+it would hardly be accepted that information that is not understood by a
+certain program is just removed.
- The example passes a simple integer as context, but an application could
- e.g. pass a struct that will contain the information for the
- header. In the end callback, the application could then e.g. do some
- finalizing operations on the struct to put it in its database.
+ Therefore, the second level of callbacks involves a "default callback".
+ An application needs to subscribe to callbacks for tags it does support,
+ and need to provide a "default callback" which will be called for tags
+it doesn't support. The application can then choose to just store
+the information that comes via the default callback in plain textual format.
- (Note that the Gedcom_val type for the xref
-argument was not discussed, see further for this)
+ After this introduction, let's see what the API looks like...
-
- Callbacks for elements
- We will now retrieve the SOUR field (the name of the program that wrote
- the file) from the header:
-
- Gedcom_ctxt my_header_source_start_cb(Gedcom_ctxt
- parent,
-
- int
- level,
-
- char*
- tag,
-
- char*
- raw_value,
-
- int
- parsed_tag,
-
- Gedcom_val
- parsed_value)
- {
- char *source = GEDCOM_STRING(parsed_value);
- printf("This file was written by %s\n", source);
- return parent;
- }
+
+ Start and end callbacks
+
+ Callbacks for records
+
+ As a simple example, we will get some information from the header of
+a GEDCOM file. First, have a look at the following piece of code:
+
+ Gedcom_ctxt my_header_start_cb (int level,
+
+
+ Gedcom_val xref,
+
+ char *tag,
+
+ char *raw_value,
+
+ int parsed_tag,
+
+ Gedcom_val parsed_value)
+ {
+ printf("The header starts\n");
+ return (Gedcom_ctxt)1;
+ }
- void my_header_source_end_cb(Gedcom_ctxt parent,
-
- Gedcom_ctxt self,
-
- Gedcom_val parsed_value)
- {
- printf("End of the source description\n");
- }
+ void my_header_end_cb (Gedcom_ctxt self)
+ {
+ printf("The header ends, context is %d\n", (int)self); /* context
+ will print as "1" */
+ }
- ...
- gedcom_subscribe_to_element(ELT_HEAD_SOUR,
-
- my_header_source_start_cb,
-
- my_header_source_end_cb);
- ...
- result = gedcom_parse_file("myfamily.ged");
+ ...
+ gedcom_subscribe_to_record(REC_HEAD, my_header_start_cb,
+ my_header_end_cb);
+ ...
+ result = gedcom_parse_file("myfamily.ged");
- The subscription mechanism for elements is similar, only the signatures
- of the callbacks differ. The signature for the start callback shows
- that the context of the parent line (e.g. the struct that describes
- the header) is passed to this start callback. The callback itself returns
- here the same context, but this can be its own context object of course.
- The end callback is called with both the context of the parent and
-the context of itself, which will be the same in the example. Again,
-the list of identifiers to use as a first argument for the subscription function
-are detailed in the interface
-details .
+ Using the gedcom_subscribe_to_record function, the application
+ requests to use the specified callbacks as start and end callback. The end
+ callback is optional: you can pass NULL if you are not interested
+ in the end callback. The identifiers to use as first argument to
+the function (here REC_HEAD) are described in the
+ interface details.
- If we look at the other arguments of the start callback, we see the level
- number (the initial number of the line in the GEDCOM file), the tag (e.g.
- "SOUR"), and then a raw value, a parsed tag and a parsed value. The
-raw value is just the raw string that occurs as value on the line next to
-the tag (in UTF-8 encoding). The parsed value is the meaningful value
-that is parsed from that raw string. The parsed tag is described in
-the section for record callbacks.
+ From the name of the function it becomes clear that this function is
+specific to complete records. For the separate elements in records
+there is another function, which we'll see shortly. Again, the callbacks
+need to have the signatures as shown in the example.
- The Gedcom_val type is meant to be an opaque type. The
- only thing that needs to be known about it is that it can contain specific
- data types, which have to be retrieved from it using pre-defined macros.
- These data types are described in the
- interface details.
-
- Some extra notes:
-
+ The Gedcom_ctxt type that is used as a result of the start
+ callback and as an argument to the end callback is vital for passing context
+ necessary for the application. This type is meant to be opaque; in
+ fact, it's a void pointer, so you can pass anything via it. The important
+ thing to know is that the context that the application returns in the start
+ callback will be passed in the end callback as an argument, and as we will
+ see shortly, also to all the directly subordinate elements of the record.
+
+ The tag is the GEDCOM tag in string format, the parsed_tag
+ is an integer, for which symbolic values are defined as TAG_HEAD,
+ TAG_SOUR, TAG_DATA, ... and USERTAG gedcom-tags.h that is installed, and included via
+ gedcom.h (so no need to include gedcom-tags.h yourself).
+
+ The example passes a simple integer as context, but an application could
+ e.g. pass a struct (or an object in a C++ application) that will contain the information for the
+ header. In the end callback, the application could then e.g. do some
+ finalizing operations on the struct to put it in its database.
+
+ (Note that the Gedcom_val type for the xref
+ and parsed_value arguments was not discussed, see further
+for this)
+
+
+ Callbacks for elements
+ We will now retrieve the SOUR field (the name of the program that wrote
+ the file) from the header:
+
+ Gedcom_ctxt my_header_source_start_cb(Gedcom_ctxt
+ parent,
+
+ int
+ level,
+
+ char*
+ tag,
+
+ char*
+ raw_value,
+
+ int
+ parsed_tag,
+
+ Gedcom_val
+ parsed_value)
+ {
+ char *source = GEDCOM_STRING(parsed_value);
+ printf("This file was written by %s\n", source);
+ return parent;
+ }
+
+ void my_header_source_end_cb(Gedcom_ctxt parent,
+
+ Gedcom_ctxt self,
+
+ Gedcom_val parsed_value)
+ {
+ printf("End of the source description\n");
+ }
+
+ ...
+ gedcom_subscribe_to_element(ELT_HEAD_SOUR,
+
+ my_header_source_start_cb,
+
+ my_header_source_end_cb);
+ ...
+ result = gedcom_parse_file("myfamily.ged");
+
+ The subscription mechanism for elements is similar, only the signatures
+ of the callbacks differ. The signature for the start callback shows
+ that the context of the parent line (here e.g. the struct that
+describes the header) is passed to this start callback. The callback
+itself returns here in this example the same context, but this can be its own context object
+of course. The end callback is called with both the context of the
+parent and the context of itself, which in this example will be the same.
+ Again, the list of identifiers to use as a first argument for the
+subscription function are detailed in the
+ interface details .
+
+ If we look at the other arguments of the start callback, we see the
+level number (the initial number of the line in the GEDCOM file), the tag
+(e.g. "SOUR"), and then a raw value, a parsed tag and a parsed value. The
+ raw value is just the raw string that occurs as value on the line next to
+ the tag (in UTF-8 encoding). The parsed value is the meaningful value
+ that is parsed from that raw string. The parsed tag is described in
+ the section for record callbacks above.
+
+ The Gedcom_val type is meant to be an opaque type. The
+ only thing that needs to be known about it is that it can contain specific
+ data types, which have to be retrieved from it using pre-defined macros.
+ These data types are described in the
+ interface details.
+
+ Some extra notes:
+
- - The
Gedcom_val argument of the end callback
- is currently not used. It is there for future enhancements.
- - There is also a
Gedcom_val argument in the
- start callback for records. This argument is currently a string value
- giving the pointer in string form.
-
+ - The
Gedcom_val argument of the end callback
+ is currently not used. It is there for future enhancements.
+ - There are also two
Gedcom_val arguments in
+the start callback for records. The first one (xref) contains the xref_value corresponding to the cross-reference (or NULL if there isn't one), the second one (parsed_value) contains the value that is parsed from the raw_value. See the interface details.
+
-
+
Default callbacks
-
- As described above, an application doesn't always implement the entire
-GEDCOM spec, and application-specific tags may have been added by other applications.
+
+ As described above, an application doesn't always implement the entire
+ GEDCOM spec, and application-specific tags may have been added by other applications.
To preserve this extra data anyway, a default callback can be registered
by the application, as in the following example:
-
+
void my_default_cb (Gedcom_ctxt parent,
- int level, char* tag, char* raw_value, int parsed_tag)
- {
- ...
- }
-
- ...
- gedcom_set_default_callback(my_default_cb);
- ...
- result = gedcom_parse_file("myfamily.ged");
-
- This callback has a similar signature as the previous ones,
-but it doesn't contain a parsed value. However, it does contain the
-parent context, that was returned by the application for the most specific
-containing tag that the application supported.
-
- Suppose e.g. that this callback is called for some tags in the header that
- are specific to some other application, then our application could make
+ int level, char* tag, char* raw_value, int parsed_tag)
+ {
+ ...
+ }
+
+ ...
+ gedcom_set_default_callback(my_default_cb);
+ ...
+ result = gedcom_parse_file("myfamily.ged");
+
+ This callback has a similar signature as the previous ones,
+ but it doesn't contain a parsed value. However, it does contain the
+ parent context, that was returned by the application for the most specific
+ containing tag that the application supported.
+
+ Suppose e.g. that this callback is called for some tags in the header
+that are specific to some other application, then our application could make
sure that the parent context contains the struct or object that represents
-the header, and use the default callback here to add the level, tag and
+ the header, and use the default callback here to add the level, tag and
raw_value as plain text in a member of that struct or object, thus preserving
the information. The application can then write this out when the
data is saved again in a GEDCOM file. To make it more specific, consider
-the following example:
-
+ the following example:
+
struct header {
- char* source;
- ...
- char* extra_text;
- };
-
- Gedcom_ctxt my_header_start_cb(int level, Gedcom_val xref, char* tag, int
-parsed_tag)
- {
- struct header head = my_make_header_struct();
- return (Gedcom_ctxt)head;
- }
-
- void my_default_cb(Gedcom_ctxt parent, int level, char* tag, char* raw_value,
-int parsed_tag)
- {
- struct header head = (struct header)parent;
- my_header_add_to_extra_text(head, level, tag, raw_value);
- }
-
- gedcom_set_default_callback(my_default_cb);
- gedcom_subscribe_to_record(REC_HEAD, my_header_start, NULL);
- ...
- result = gedcom_parse_file(filename);
-
- Note that the default callback will be called for any tag that isn't specifically
- subscribed upon by the application, and can thus be called in various contexts.
- For simplicity, the example above doesn't take this into account (the
- parent could be of different types, depending
-on the context).
-
-
+ char* source;
+ ...
+ char* extra_text;
+ };
+
+ Gedcom_ctxt my_header_start_cb(int level, Gedcom_val xref, char* tag,
+char *raw_value,
+
+ int parsed_tag, Gedcom_val parsed_value)
+ {
+ struct header head = my_make_header_struct();
+ return (Gedcom_ctxt)head;
+ }
+
+ void my_default_cb(Gedcom_ctxt parent, int level, char* tag, char* raw_value,
+ int parsed_tag)
+ {
+ struct header head = (struct header)parent;
+ my_header_add_to_extra_text(head, level, tag, raw_value);
+ }
+
+ gedcom_set_default_callback(my_default_cb);
+ gedcom_subscribe_to_record(REC_HEAD, my_header_start, NULL);
+ ...
+ result = gedcom_parse_file(filename);
+
+ Note that the default callback will be called for any tag that isn't
+specifically subscribed upon by the application, and can thus be called
+in various contexts. For simplicity, the example above doesn't take
+this into account (the parent could be of different
+types, depending on the context).
+
+Note also that the default callback is not called when the parent context is NULL
+
+
+
Other API functions
-
- Although the above describes the basic interface of libgedcom, there are
- some other functions that allow to customize the behaviour of the library.
- These will be explained in the current section.
-
+
+ Although the above describes the basic interface of libgedcom, there
+are some other functions that allow to customize the behaviour of the library.
+ These will be explained in the current section.
+
Debugging
- The library can generate various debugging output, not only from itself,
- but also the debugging output generated by the yacc parser. By default,
- no debugging output is generated, but this can be customized using the following
- function:
-
+ The library can generate various debugging output, not only from itself,
+ but also the debugging output generated by the yacc parser. By default,
+ no debugging output is generated, but this can be customized using the
+following function:
+
void gedcom_set_debug_level (int level,
- FILE* trace_output)
-
- The level can be one of the following values:
-
+ FILE* trace_output)
+
+ The level can be one of the following values:
+
- - 0: no debugging information (this is the default)
- - 1: only debugging information from libgedcom
- itself
- - 2: debugging information from libgedcom and
-yacc
-
+ - 0: no debugging information (this is the
+default)
+ - 1: only debugging information from libgedcom
+ itself
+ - 2: debugging information from libgedcom and
+ yacc
+
- If the trace_output is NULL, debugging information
- will be written to stderr, otherwise the given file handle
+ If the trace_output is NULL, debugging information
+ will be written to stderr, otherwise the given file handle
is used (which must be open).
-
-
+
+
Error treatment
- One of the previous sections already described the callback to be registered
- to get error messages. The library also allows to customize what happens
- on an error, using the following function:
-
+ One of the previous sections already described the callback to be registered
+ to get error messages. The library also allows to customize what
+happens on an error, using the following function:
+
void gedcom_set_error_handling (Gedcom_err_mech
- mechanism)
-
- The mechanism can be one of:
-
+ mechanism)
+
+ The mechanism can be one of:
+
+
- IMMED_FAIL: immediately fail the parsing
- on an error (this is the default)DEFER_FAIL: continue parsing after
-an error, but return a failure code eventuallyIGNORE_ERRORS: continue parsing after
- an error, return success alwaysIMMED_FAIL: immediately fail the
+parsing on an error (this is the default)DEFER_FAIL: continue parsing after
+ an error, but return a failure code eventuallyIGNORE_ERRORS: continue parsing
+after an error, return success always
- This doesn't influence the generation of error or warning messages, only
- the behaviour of the parser and its return code.
-
-
+ This doesn't influence the generation of error or warning messages, only
+ the behaviour of the parser and its return code.
+
+
+
Compatibility mode
-
- Applications are not necessarily true to the GEDCOM spec (or use a different
- version than 5.5). The intention is that the library is resilient
+
+ Applications are not necessarily true to the GEDCOM spec (or use a different
+ version than 5.5). The intention is that the library is resilient
to this, and goes in compatibility mode for files written by specific programs
- (detected via the HEAD.SOUR tag). This compatibility mode can be enabled
- and disabled via the following function:
-
+ (detected via the HEAD.SOUR tag). This compatibility mode can be
+enabled and disabled via the following function:
+
+
void gedcom_set_compat_handling
- (int enable_compat)
-
- The argument can be:
-
+ (int enable_compat)
+
+ The argument can be:
+
+
- - 0: disable compatibility mode
- - 1: allow compatibility mode (this is the default)
-
-
+ - 0: disable compatibility mode
+ - 1: allow compatibility mode (this is the default)
+
+
+
- Note that, currently, no actual compatibility code is present, but this
-is on the to-do list.
-
-
- $Id$
$Name$
-
+ Note that, currently, no actual compatibility code is present, but this
+ is on the to-do list.
+
+
+
+
+ $Id$
$Name$
+
-
-
-
+
+
+
\ No newline at end of file