X-Git-Url: https://git.dlugolecki.net.pl/?a=blobdiff_plain;f=doc%2Fusage.html;h=00003be0d0b4484dd762b1c4b4e7c0b174d1065f;hb=b1a87b467d9c6b38aa4a2b2e4537b0deff9a251e;hp=2843d7c528b8c8fa5765eab45601b3fc8407b5c7;hpb=8c92a223c34fbd674f26520fb990c64a7b2f9147;p=gedcom-parse.git diff --git a/doc/usage.html b/doc/usage.html index 2843d7c..00003be 100644 --- a/doc/usage.html +++ b/doc/usage.html @@ -1,435 +1,563 @@ - - -
-libgedcom.so
), to be linked in the application
- programgedcom.h
), to be used in the sources
- of the application programgedcom-tags.h
) that is also installed,
-but that is automatically included via gedcom.h
libgedcom.so
), to be linked in the application
+ programgedcom.h
), to be used in the sources
+ of the application programgedcom-tags.h
) that is also installed,
+ but that is automatically included via gedcom.h
$PREFIX/share/gedcom-parse
- that contains some additional stuff, but which is not immediately important
- at first. I'll leave the description of the data directory for later.int result;
- ...
- result = gedcom_parse_file("myfamily.ged");
-
- Although this will not provide much information, one thing it does is
-parse the entire file and return the result. The function returns 0
-on success and 1 on failure. No other information is available using
-this function only.$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.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.- In the above piece of code,void my_message_handler (Gedcom_msg_type type, - char *msg)
- {
- ...
- }
- ...
- gedcom_set_message_handler(my_message_handler);
- ...
- result = gedcom_parse_file("myfamily.ged");
-
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:- 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.Error on line
<lineno>: <actual_message>
+ char *msg)
+ {
+ ...
+ }
+ ...
+ gedcom_set_message_handler(my_message_handler);
+ ...
+ result = gedcom_parse_file("myfamily.ged");
printf
- is used in the message handler.+ 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.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:
+ +- Using theError on line
<lineno>: <actual_message>
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 passNULL
if you are not interested - in the end callback. The identifiers to use as first argument to the - function (hereREC_HEAD
) are described in the - interface details.
+ Note that the entire string will be properly internationalized, and +encoded in UTF-8 (Why UTF-8?). 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.
- 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.
+ 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.
- TheGedcom_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.
-
-Thetag
is the GEDCOM tag in string format, theparsed_tag
- is an integer, for which symbolic values are defined asTAG_HEAD,
-TAG_SOUR,
TAG_DATA,
... andUSERTAG
-for the application-specific tags. These values are defined in the -header
gedcom-tags.h
that is installed, and included via-gedcom.h
(so no need to includegedcom-tags.h
yourself).
+ 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 example passes a simple integer as context, but an application could - e.g. pass astruct
that will contain the information for the - header. In the end callback, the application could then e.g. do some - finalizing operations on thestruct
to put it in its database.
+ 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.
- (Note that theGedcom_val
type for thexref
-argument was not discussed, see further for this)
+ 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.
- -Callbacks for elements
- We will now retrieve the SOUR field (the name of the program that wrote - the file) from the header:
- -- 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. theGedcom_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;
- }
+ 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,
+ + 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");
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 thegedcom_subscribe_to_record
function, the application + requests to use the specified callbacks as start and end callback. The end + callback is optional: you can passNULL
if you are not interested + in the end callback. The identifiers to use as first argument to +the function (hereREC_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.
- TheGedcom_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:
- + TheGedcom_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.
+
+ Thetag
is the GEDCOM tag in string format, theparsed_tag
+ is an integer, for which symbolic values are defined asTAG_HEAD,
+TAG_SOUR,
TAG_DATA,
... andUSERTAG
+ for the application-specific tags. These values are defined in the + header
gedcom-tags.h
that is installed, and included via+ gedcom.h
(so no need to includegedcom-tags.h
yourself).
+
+ The example passes a simple integer as context, but an application could + e.g. pass astruct
(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 thestruct
to put it in its database.
+
+ (Note that theGedcom_val
type for thexref
+ andparsed_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:
+ ++ 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. theGedcom_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");
+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.
+
+ TheGedcom_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 thexref_value
corresponding to the cross-reference (orNULL
if there isn't one), the second one (parsed_value
) contains the value that is parsed from theraw_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:
-
- +- 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.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");
-
-
- 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");
+
- 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 -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);
-
parent
could be of different types, depending
-on the context).parent
could be of different
+types, depending on the context).NULL
. This is e.g. the case if none of the "upper" tags has been subscribed upon.- Thevoid gedcom_set_debug_level (int level, - FILE* trace_output)
-
level
can be one of the following values:level
can be one of the following values: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).- Thevoid gedcom_set_error_handling (Gedcom_err_mech - mechanism)
-
mechanism
can be one of: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- The argument can be:void gedcom_set_compat_handling - (int enable_compat)
-
$Id$- + Note that, currently, no actual compatibility code is present, but this + is on the to-do list.
$Name$
locale
mechanism (i.e. via the LANG
, LC_ALL
or LC_CTYPE
environment variables), which also controls the gettext
+ mechanism in the application. For this, the following steps need to
+be taken by the application (more detailed info can be found in the info
+file of the GNU libc library in the "Generic Charset Conversion" section
+under "Character Set Handling" or online here):+++++#include <locale.h> /* for setlocale */
#include <langinfo.h> /* for nl_langinfo */
#include <iconv.h> /* for iconv_* functions */
+++++setlocale(LC_ALL, "");
+++++iconv_t iconv_handle;
...
iconv_handle = iconv_open(nl_langinfo(CODESET), "UTF-8");
if (iconv_handle == (iconv_t) -1)
/* signal an error */
+++++/* char* in_buf is the input buffer, size_t in_len is its length */
/* char* out_buf is the output buffer, size_t out_len is its length */
size_t nconv;
char *in_ptr = in_buf;
char *out_ptr = out_buf;
nconv = iconv(iconv_handle, &in_ptr, &in_len, &out_ptr, &out_len);
If the output buffer is not big enough,+iconv
will return -1 and seterrno
toE2BIG
. Also, thein_ptr
andout_ptr
will point just after the last successfully converted character in the respective buffers, and thein_len
andout_len
will be updated to show the remaining lengths. There can be two strategies here:
++
+Another error case is when the conversion was unsuccessful (if one of the +characters can't be represented in the target character set). The- Make sure from the beginning +that the output buffer is big enough. However, it's difficult to find +an absolute maximum length in advance, even given the length of the input +string.
+
+
+- Do the conversion in several steps, growing the output buffer each time to make more space, and calling
+iconv
+ consecutively until the conversion is complete. This is the preferred +way (a function could be written to encapsulate all this).iconv
function will then also return -1 and seterrno
toEILSEQ
; thein_ptr
will point to the character that couldn't be converted. In that case, again two strategies are possible:
++
+- Just fail the conversion, and show an error. This is not very user friendly, of course.
+
+
+- Skip over the character that can't be converted and append a "?" to the output buffer, then call
+iconv
again. Skipping over a UTF-8 character is fairly simple, as follows from the encoding rules:+
++
+- if the first byte is in binary 0xxxxxxx, then the character is only one byte long, just skip over that byte
+
+
+- if the first byte is in binary 11xxxxxx, then skip over that byte and all bytes 10xxxxxx that follow.
+
+
++ + + + The source distribution of+++iconv_close(iconv_handle);
gedcom-parse
contains an example implementation (utf8-locale.c
and utf8-locale.h
+ in the top directory) that grows the output buffer dynamically and outputs
+"?" for characters that can't be converted. Feel free to use it in
+your source code (it is not part of the library, and it isn't installed anywhere,
+so you need to take over the source and header file in your application).
+ ++Both functions return a pointer to a static buffer that is overwritten on +each call. To function properly, the application must first set the +locale using the+char *convert_utf8_to_locale (char *input);
char *convert_locale_to_utf8 (char *input);
setlocale
function (the second step above).
+ All other steps, including setting up and closing down the conversion
+handles, are transparantly handled by the two functions.+++void convert_set_unknown (const char *unknown);
$Id$+
$Name$
- - - + + + \ No newline at end of file