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* gdbint.texinfo (User Interface): A new section about ui_out

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functions, based on text written by Fernando Nasser.
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@ -1,5 +1,8 @@
2001-04-01 Eli Zaretskii <eliz@is.elta.co.il>
* gdbint.texinfo (User Interface): A new section about ui_out
functions, based on text written by Fernando Nasser.
* stabs.texinfo: Change Permissions to GFDL. Update Copyright.
2001-03-26 Eli Zaretskii <eliz@is.elta.co.il>

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gdb/doc/gdbint.texinfo
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@ -717,6 +717,7 @@ is the most common and most familiar, there are others.
@section Command Interpreter
@cindex command interpreter
@cindex CLI
The command interpreter in @value{GDBN} is fairly simple. It is designed to
allow for the set of commands to be augmented dynamically, and also
has a recursive subcommand capability, where the first argument to
@ -747,6 +748,588 @@ replacement (if one exists). Note that the replacement string passed to
@code{deprecate_cmd} should be the full name of the command, i.e. the
entire string the user should type at the command line.
@section UI-Independent Output---the @code{ui_out} Functions
@c This section is based on the documentation written by Fernando
@c Nasser <fnasser@redhat.com>.
@cindex @code{ui_out} functions
The @code{ui_out} functions present an abstraction level for the
@value{GDBN} output code. They hide the specifics of different user
interfaces supported by @value{GDBN}, and thus free the programmer
from the need to write several versions of the same code, one each for
every UI, to produce output.
@subsection Overview and Terminology
In general, execution of each @value{GDBN} command produces some sort
of output, and can even generate an input request.
Output can be generated for the following purposes:
@itemize @bullet
@item
to display a @emph{result} of an operation;
@item
to convey @emph{info} or produce side-effects of a requested
operation;
@item
to provide a @emph{notification} of an asynchronous event (including
progress indication of a prolonged asynchronous operation);
@item
to display @emph{error messages} (including warnings);
@item
to show @emph{debug data};
@item
to @emph{query} or prompt a user for input (a special case).
@end itemize
@noindent
This section mainly concentrates on how to build result output,
although some of it also applies to other kinds of output.
Generation of output that displays the results of an operation
involves one or more of the following:
@itemize @bullet
@item
output of the actual data
@item
formatting the output as appropriate for console output, to make it
easily readable by humans
@item
machine oriented formatting--a more terse formatting to allow for easy
parsing by programs which read @value{GDBN}'s output
@item
annotation, whose purpose is to help a GUI (such as GDBTK or Emacs) to
identify interesting parts in the output
@end itemize
The @code{ui_out} routines take care of the first three aspects.
Annotations are provided by separate annotation routines. Note that
use of annotations for an interface between a GUI and @value{GDBN} is
deprecated.
Output can be in the form of a single item, which we call a
@dfn{field}; a @dfn{list} of fields; or a @dfn{table}, which is a list
of fields with a header. In a BNF-like form:
@example
<field> ::= any single item of data kept by gdb ;;
<list> ::= @{ <field> @} ;;
<table> ::= <header> @{ <list> @} ;;
<header> ::= @{ <column> @} ;;
<column> ::= <width> <alignment> <title> ;;
@end example
@subsection General Conventions
All @code{ui_out} routines currently are of type @code{void}, except
for @code{ui_out_stream_new} which returns a pointer to the newly
created object.
The first parameter is always the @code{ui_out} vector object, a
pointer to a @code{struct ui_out}.
The @var{format} parameter is like in @code{printf} family of
functions. When it is present, there is usually also a variable list
of arguments used to satisfy the @code{%} specifiers in the supplied
format.
When a character string argument is not used in a @code{ui_out}
function call, a @code{NULL} pointer has to be supplied instead.
@subsection Table and List Functions
@cindex list output functions
@cindex table output functions
This section introduces @code{ui_out} routines for building lists and
tables. The routines to output the actual data items (fields) are
presented in the next section.
To recap: A @dfn{list} is a sequence of @dfn{fields} with information
about an object; a @dfn{table} is a list of lists, each on a separate
line, prefixed by a @dfn{header} line with the column @dfn{titles}.
Use the table functions if your output is composed of a list of fields
for several objects and the console output should have a header. Use
this even when you are listing just one object but you still want the
header.
Use the list functions for the output of each object of a table or if
your output consists of a single list of fields.
You can nest a list into a table, but not the other way around.
@cindex nesting level in @code{ui_out} functions
Lists can also be nested: some of your fields may be lists or
@dfn{tuples}--@code{@{@var{name},@var{value}@}} pairs. The maximum
nesting level is currently 4.
The overall structure of the table output code is something like this:
@example
ui_out_table_begin
ui_out_table_header
...
ui_out_table_body
ui_out_list_begin
ui_out_field_*
...
ui_out_list_end
...
ui_out_table_end
@end example
Here's the description of table- and list-related @code{ui_out}
functions:
@deftypefun void ui_out_table_begin (struct ui_out *@var{uiout}, int @var{nbrofcols}, char *@var{tblid})
The function @code{ui_out_table_begin} marks the beginning of the
output of a table. It should always be called before any other
@code{ui_out} function for a given table. @var{nbrofcols} is the
number of columns in the table, and @var{tblid} is an optional string
identifying the table. The string pointed to by @var{tblid} is copied
by the implementation of @code{ui_out_table_begin}, so the application
can free the string if it was @code{malloc}ed.
The companion function @code{ui_out_table_end}, described below, marks
the end of the table's output.
@end deftypefun
@deftypefun void ui_out_table_header (struct ui_out *@var{uiout}, int @var{width}, enum ui_align @var{alignment}, char *@var{colhdr})
@code{ui_out_table_header} provides the header information for a
single table column. You call this function several times, one each
for every column of the table, after @code{ui_out_table_begin}, but
before @code{ui_out_table_body}.
The value of @var{width} gives the column width in characters. The
value of @var{alignment} is one of @code{left}, @code{center}, and
@code{right}, and it specifies how to align the header: left-justify,
center, or right-justify it. @var{colhdr} points to a string that
specifies the column header; the implementation copies that string, so
column header strings in @code{malloc}ed storage can be freed after
the call.
@end deftypefun
@deftypefun void ui_out_table_body (struct ui_out *@var{uiout})
This function marks the end of header information and the beginning of
table body output. It doesn't by itself produce any data output; that
is done by the list and field output functions described below.
@end deftypefun
@deftypefun void ui_out_table_end (struct ui_out *@var{uiout})
This function signals the end of a table's output. It should be
called after the table body has been produced by the list and field
output functions.
There should be exactly one call to @code{ui_out_table_end} for each
call to @code{ui_out_table_begin}, otherwise the @code{ui_out}
functions will signal an internal error.
@end deftypefun
The output of the lists that represent the table rows must follow the
call to @code{ui_out_table_body} and precede the call to
@code{ui_out_table_end}. You produce the lists by calling
@code{ui_out_list_begin} and @code{ui_out_list_end}, with suitable
calls to functions which actually output fields between them.
@deftypefun void ui_out_list_begin (struct ui_out *@var{uiout}, char *@var{lstid})
This function marks the beginning or a list output. @var{lstid}
points to an optional string that identifies the list; it is copied by
the implementation, and so strings in @code{malloc}ed storage can be
freed after the call.
@end deftypefun
@deftypefun void ui_out_list_end (struct ui_out *@var{uiout})
This function signals an end of a list output. There should be
exactly one call to @code{ui_out_list_end} for each call to
@code{ui_out_list_begin}, otherwise an internal @value{GDBN} error
will be signaled.
@end deftypefun
@subsection Item Output Functions
@cindex item output functions
@cindex field output functions
@cindex data output
The functions described below produce output for the actual data
items, or fields, which contain information about the object.
Choose the appropriate function accordingly to your particular needs.
@deftypefun void ui_out_field_fmt (struct ui_out *@var{uiout}, char *@var{fldname}, char *@var{format}, ...)
This is the most general output function. It produces the
representation of the data in the variable-length argument list
according to formatting specifications in @var{format}, a
@code{printf}-like format string. The optional argument @var{fldname}
supplies the name of the field. The data items themselves are
supplied as additional arguments after @var{format}.
This generic function should be used only when it is not possible to
use one of the specialized versions (see below).
@end deftypefun
@deftypefun void ui_out_field_int (struct ui_out *@var{uiout}, char *@var{fldname}, int @var{value})
This function outputs a value of an @code{int} variable. It uses the
@code{"%d"} output conversion specification. @var{fldname} specifies
the name of the field.
@end deftypefun
@deftypefun void ui_out_field_core_addr (struct ui_out *@var{uiout}, char *@var{fldname}, CORE_ADDR @var{address})
This function outputs an address.
@end deftypefun
@deftypefun void ui_out_field_string (struct ui_out *@var{uiout}, char *@var{fldname}, const char *@var{string})
This function outputs a string using the @code{"%s"} conversion
specification.
@end deftypefun
Sometimes, there's a need to compose your output piece by piece using
functions that operate on a stream, such as @code{value_print} or
@code{fprintf_symbol_filtered}. These functions accept an argument of
the type @code{struct ui_file *}, a pointer to a @code{ui_file} object
used to store the data stream used for the output. When you use one
of these functions, you need a way to pass their results stored in a
@code{ui_file} object to the @code{ui_out} functions. To this end,
you first create a @code{ui_stream} object by calling
@code{ui_out_stream_new}, pass the @code{stream} member of that
@code{ui_stream} object to @code{value_print} and similar functions,
and finally call @code{ui_out_field_stream} to output the field you
constructed. When the @code{ui_stream} object is no longer needed,
you should destroy it and free its memory by calling
@code{ui_out_stream_delete}.
@deftypefun struct ui_stream *ui_out_stream_new (struct ui_out *@var{uiout})
This function creates a new @code{ui_stream} object which uses the
same output methods as the @code{ui_out} object whose pointer is
passed in @var{uiout}. It returns a pointer to the newly created
@code{ui_stream} object.
@end deftypefun
@deftypefun void ui_out_stream_delete (struct ui_stream *@var{streambuf})
This functions destroys a @code{ui_stream} object specified by
@var{streambuf}.
@end deftypefun
@deftypefun void ui_out_field_stream (struct ui_out *@var{uiout}, char *@var{fieldname}, struct ui_stream *@var{streambuf})
This function consumes all the data accumulated in
@code{streambuf->stream} and outputs it like
@code{ui_out_field_string} does. After a call to
@code{ui_out_field_stream}, the accumulated data no longer exists, but
the stream is still valid and may be used for producing more fields.
@end deftypefun
@strong{Important:} If there is any chance that your code could bail
out before completing output generation and reaching the point where
@code{ui_out_stream_delete} is called, it is necessary to set up a
cleanup, to avoid leaking memory and other resources. Here's a
skeleton code to do that:
@smallexample
struct ui_stream *mybuf = ui_out_stream_new (uiout);
struct cleanup *old = make_cleanup (ui_out_stream_delete, mybuf);
...
do_cleanups (old);
@end smallexample
If the function already has the old cleanup chain set (for other kinds
of cleanups), you just have to add your cleanup to it:
@smallexample
mybuf = ui_out_stream_new (uiout);
make_cleanup (ui_out_stream_delete, mybuf);
@end smallexample
Note that with cleanups in place, you should not call
@code{ui_out_stream_delete} directly, or you would attempt to free the
same buffer twice.
@subsection Utility Output Functions
@deftypefun void ui_out_field_skip (struct ui_out *@var{uiout}, char *@var{fldname})
This function skips a field in a table. Use it if you have to leave
an empty field without disrupting the table alignment. The argument
@var{fldname} specifies a name for the (missing) filed.
@end deftypefun
@deftypefun void ui_out_text (struct ui_out *@var{uiout}, char *@var{string})
This function outputs the text in @var{string} in a way that makes it
easy to be read by humans. For example, the console implementation of
this method filters the text through a built-in pager, to prevent it
from scrolling off the visible portion of the screen.
Use this function for printing relatively long chunks of text around
the actual field data: the text it produces is not aligned according
to the table's format. Use @code{ui_out_field_string} to output a
string field, and use @code{ui_out_message}, described below, to
output short messages.
@end deftypefun
@deftypefun void ui_out_spaces (struct ui_out *@var{uiout}, int @var{nspaces})
This function outputs @var{nspaces} spaces. It is handy to align the
text produced by @code{ui_out_text} with the rest of the table or
list.
@end deftypefun
@deftypefun void ui_out_message (struct ui_out *@var{uiout}, int @var{verbosity}, char *@var{format}, ...)
This function produces a formatted message, provided that the current
verbosity level is at least as large as given by @var{verbosity}. The
current verbosity level is specified by the user with the @samp{set
verbositylevel} command.@footnote{As of this writing (April 2001),
setting verbosity level is not yet implemented, and is always returned
as zero. So calling @code{ui_out_message} with a @var{verbosity}
argument more than zero will cause the message to never be printed.}
@end deftypefun
@deftypefun void ui_out_wrap_hint (struct ui_out *@var{uiout}, char *@var{indent})
This function gives the console output filter (a paging filter) a hint
of where to break lines which are too long. Ignored for all other
output consumers. @var{indent}, if non-@code{NULL}, is the string to
be printed to indent the wrapped text on the next line; it must remain
accessible until the next call to @code{ui_out_wrap_hint}, or until an
explicit newline is produced by one of the other functions. If
@var{indent} is @code{NULL}, the wrapped text will not be indented.
@end deftypefun
@deftypefun void ui_out_flush (struct ui_out *@var{uiout})
This function flushes whatever output has been accumulated so far, if
the UI buffers output.
@end deftypefun
@subsection Examples of Use of @code{ui_out} functions
@cindex using @code{ui_out} functions
@cindex @code{ui_out} functions, usage examples
This section gives some practical examples of using the @code{ui_out}
functions to generalize the old console-oriented code in
@value{GDBN}. The examples all come from functions defined on the
@file{breakpoints.c} file.
This example, from the @code{breakpoint_1} function, shows how to
produce a table.
The original code was:
@example
if (!found_a_breakpoint++)
@{
annotate_breakpoints_headers ();
annotate_field (0);
printf_filtered ("Num ");
annotate_field (1);
printf_filtered ("Type ");
annotate_field (2);
printf_filtered ("Disp ");
annotate_field (3);
printf_filtered ("Enb ");
if (addressprint)
@{
annotate_field (4);
printf_filtered ("Address ");
@}
annotate_field (5);
printf_filtered ("What\n");
annotate_breakpoints_table ();
@}
@end example
Here's the new version:
@example
if (!found_a_breakpoint++)
@{
annotate_breakpoints_headers ();
if (addressprint)
ui_out_table_begin (ui, 6);
else
ui_out_table_begin (ui, 5);
annotate_field (0);
ui_out_table_header (ui, 4, left, "Num");
annotate_field (1);
ui_out_table_header (ui, 15, left, "Type");
annotate_field (2);
ui_out_table_header (ui, 5, left, "Disp");
annotate_field (3);
ui_out_table_header (ui, 4, left, "Enb");
if (addressprint)
@{
annotate_field (4);
ui_out_table_header (ui, 11, left, "Address");
@}
annotate_field (5);
ui_out_table_header (ui, 40, left, "What");
ui_out_table_body (ui);
annotate_breakpoints_table ();
@}
@end example
This example, from the @code{print_one_breakpoint} function, shows how
to produce the actual data for the table whose structure was defined
in the above example. The original code was:
@example
annotate_record ();
annotate_field (0);
printf_filtered ("%-3d ", b->number);
annotate_field (1);
if ((int)b->type > (sizeof(bptypes)/sizeof(bptypes[0]))
|| ((int) b->type != bptypes[(int) b->type].type))
internal_error ("bptypes table does not describe type #%d.",
(int)b->type);
printf_filtered ("%-14s ", bptypes[(int)b->type].description);
annotate_field (2);
printf_filtered ("%-4s ", bpdisps[(int)b->disposition]);
annotate_field (3);
printf_filtered ("%-3c ", bpenables[(int)b->enable]);
@end example
This is the new version:
@example
annotate_record ();
ui_out_list_begin (uiout, "bkpt");
annotate_field (0);
ui_out_field_int (uiout, "number", b->number);
annotate_field (1);
if (((int) b->type > (sizeof (bptypes) / sizeof (bptypes[0])))
|| ((int) b->type != bptypes[(int) b->type].type))
internal_error ("bptypes table does not describe type #%d.",
(int) b->type);
ui_out_field_string (uiout, "type", bptypes[(int)b->type].description);
annotate_field (2);
ui_out_field_string (uiout, "disp", bpdisps[(int)b->disposition]);
annotate_field (3);
ui_out_field_fmt (uiout, "enabled", "%c", bpenables[(int)b->enable]);
@end example
This example, also from @code{print_one_breakpoint}, shows how to
produce a complicated output field using the @code{print_expression}
functions which requires a stream to be passed. It also shows how to
automate stream destruction with cleanups. The original code was:
@example
annotate_field (5);
print_expression (b->exp, gdb_stdout);
@end example
The new version is:
@example
struct ui_stream *stb = ui_out_stream_new (uiout);
struct cleanup *old_chain = make_cleanup_ui_out_stream_delete (stb);
...
annotate_field (5);
print_expression (b->exp, stb->stream);
ui_out_field_stream (uiout, "what", local_stream);
@end example
This example, also from @code{print_one_breakpoint}, shows how to use
@code{ui_out_text} and @code{ui_out_field_string}. The original code
was:
@example
annotate_field (5);
if (b->dll_pathname == NULL)
printf_filtered ("<any library> ");
else
printf_filtered ("library \"%s\" ", b->dll_pathname);
@end example
It became:
@example
annotate_field (5);
if (b->dll_pathname == NULL)
@{
ui_out_field_string (uiout, "what", "<any library>");
ui_out_spaces (uiout, 1);
@}
else
@{
ui_out_text (uiout, "library \"");
ui_out_field_string (uiout, "what", b->dll_pathname);
ui_out_text (uiout, "\" ");
@}
@end example
The following example from @code{print_one_breakpoint} shows how to
use @code{ui_out_field_int} and @code{ui_out_spaces}. The original
code was:
@example
annotate_field (5);
if (b->forked_inferior_pid != 0)
printf_filtered ("process %d ", b->forked_inferior_pid);
@end example
It became:
@example
annotate_field (5);
if (b->forked_inferior_pid != 0)
@{
ui_out_text (uiout, "process ");
ui_out_field_int (uiout, "what", b->forked_inferior_pid);
ui_out_spaces (uiout, 1);
@}
@end example
Here's an example of using @code{ui_out_field_string}. The original
code was:
@example
annotate_field (5);
if (b->exec_pathname != NULL)
printf_filtered ("program \"%s\" ", b->exec_pathname);
@end example
It became:
@example
annotate_field (5);
if (b->exec_pathname != NULL)
@{
ui_out_text (uiout, "program \"");
ui_out_field_string (uiout, "what", b->exec_pathname);
ui_out_text (uiout, "\" ");
@}
@end example
Finally, here's an example of printing an address. The original code:
@example
annotate_field (4);
printf_filtered ("%s ",
local_hex_string_custom ((unsigned long) b->address, "08l"));
@end example
It became:
@example
annotate_field (4);
ui_out_field_core_addr (uiout, "Address", b->address);
@end example
@section Console Printing
@section TUI