GDB: Add a character string limiting option

This commit splits the `set/show print elements' option into two.  We
retain `set/show print elements' for controlling how many elements of an
array we print, but a new `set/show print characters' setting is added
which is used for controlling how many characters of a string are
printed.

The motivation behind this change is to allow users a finer level of
control over how data is printed, reflecting that, although strings can
be thought of as arrays of characters, users often want to treat these
two things differently.

For compatibility reasons by default the `set/show print characters'
option is set to `elements', which makes the limit for character strings
follow the setting of the `set/show print elements' option, as it used
to.  Using `set print characters' with any other value makes the limit
independent from the `set/show print elements' setting, however it can
be restored to the default with the `set print characters elements'
command at any time.

A corresponding `-characters' option for the `print' command is added,
with the same semantics, i.e. one can use `elements' to make a given
`print' invocation follow the limit of elements, be it set with the
`-elements' option also given with the same invocation or taken from the
`set/show print elements' setting, for characters as well regardless of
the current setting of the `set/show print characters' option.

The GDB changes are all pretty straightforward, just changing references
to the old 'print_max' to use a new `get_print_max_chars' helper which
figures out which of the two of `print_max' and `print_max_chars' values
to use.

Likewise, the documentation is just updated to reference the new setting
where appropriate.

To make people's life easier the message shown by `show print elements'
now indicates if the setting also applies to character strings:

(gdb) set print characters elements
(gdb) show print elements
Limit on string chars or array elements to print is 200.
(gdb) set print characters unlimited
(gdb) show print elements
Limit on array elements to print is 200.
(gdb)

and the help text shows the dependency as well:

(gdb) help set print elements
Set limit on array elements to print.
"unlimited" causes there to be no limit.
This setting also applies to string chars when "print characters"
is set to "elements".
(gdb)

In the testsuite there are two minor updates, one to add `-characters'
to the list of completions now shown for the `print' command, and a bare
minimum pair of checks for the right handling of `set print characters'
and `show print characters', copied from the corresponding checks for
`set print elements' and `show print elements' respectively.

Co-Authored-By: Maciej W. Rozycki <macro@embecosm.com>
Approved-By: Simon Marchi <simon.marchi@efficios.com>

1 files changed, 39 insertions, 5 deletions

diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 9c0018ea5c1..b5fad2cb16e 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -10309,10 +10309,18 @@ Related setting: @ref{set print array}.
 Set printing of array indexes.
 Related setting: @ref{set print array-indexes}.
 
-@item -elements @var{number-of-elements}|@code{unlimited}
-Set limit on string chars or array elements to print.  The value
+@item -characters @var{number-of-characters}|@code{elements}|@code{unlimited}
+Set limit on string characters to print.  The value @code{elements}
+causes the limit on array elements to print to be used.  The value
 @code{unlimited} causes there to be no limit.  Related setting:
-@ref{set print elements}.
+@ref{set print characters}.
+
+@item -elements @var{number-of-elements}|@code{unlimited}
+Set limit on array elements and optionally string characters to print.
+See @ref{set print characters}, and the @code{-characters} option above
+for when this option applies to strings.  The value @code{unlimited}
+causes there to be no limit.  @xref{set print elements}, for a related
+CLI command.
 
 @item -max-depth @var{depth}|@code{unlimited}
 Set the threshold after which nested structures are replaced with
@@ -11709,6 +11717,31 @@ Don't printing binary values in groups.  This is the default.
 @item show print nibbles
 Show whether to print binary values in groups of four bits.
 
+@anchor{set print characters}
+@item set print characters @var{number-of-characters}
+@itemx set print characters elements
+@itemx set print characters unlimited
+@cindex number of string characters to print
+@cindex limit on number of printed string characters
+Set a limit on how many characters of a string @value{GDBN} will print.
+If @value{GDBN} is printing a large string, it stops printing after it
+has printed the number of characters set by the @code{set print
+characters} command.  This equally applies to multi-byte and wide
+character strings, that is for strings whose character type is
+@code{wchar_t}, @code{char16_t}, or @code{char32_t} it is the number of
+actual characters rather than underlying bytes the encoding uses that
+this setting controls.
+Setting @var{number-of-characters} to @code{elements} means that the
+limit on the number of characters to print follows one for array
+elements; see @ref{set print elements}.
+Setting @var{number-of-characters} to @code{unlimited} means that the
+number of characters to print is unlimited.
+When @value{GDBN} starts, this limit is set to @code{elements}.
+
+@item show print characters
+Display the number of characters of a large string that @value{GDBN}
+will print.
+
 @anchor{set print elements}
 @item set print elements @var{number-of-elements}
 @itemx set print elements unlimited
@@ -11717,7 +11750,8 @@ Show whether to print binary values in groups of four bits.
 Set a limit on how many elements of an array @value{GDBN} will print.
 If @value{GDBN} is printing a large array, it stops printing after it has
 printed the number of elements set by the @code{set print elements} command.
-This limit also applies to the display of strings.
+By default this limit also applies to the display of strings; see
+@ref{set print characters}.
 When @value{GDBN} starts, this limit is set to 200.
 Setting @var{number-of-elements} to @code{unlimited} or zero means
 that the number of elements to print is unlimited.
@@ -15233,7 +15267,7 @@ The optional @var{mods} changes the usual handling of the arguments.
 @code{s} requests that pointers to chars be handled as strings, in
 particular collecting the contents of the memory being pointed at, up
 to the first zero.  The upper bound is by default the value of the
-@code{print elements} variable; if @code{s} is followed by a decimal
+@code{print characters} variable; if @code{s} is followed by a decimal
 number, that is the upper bound instead.  So for instance
 @samp{collect/s25 mystr} collects as many as 25 characters at
 @samp{mystr}.