[gdb] Make execute_command_to_string return string on throw

The pattern for using execute_command_to_string is:
...
  std::string output;
  output = execute_fn_to_string (fn, term_out);
...

This results in a problem when using it in a try/catch:
...
  try
    {
      output = execute_fn_to_string (fn, term_out)
    }
  catch (const gdb_exception &e)
    {
      /* Use output.  */
    }
...

If an expection was thrown during execute_fn_to_string, then the output
remains unassigned, while it could be worthwhile to known what output was
generated by gdb before the expection was thrown.

Fix this by returning the string using a parameter instead:
...
  execute_fn_to_string (output, fn, term_out)
...

Also add a variant without string parameter, to support places where the
function is used while ignoring the result:
...
  execute_fn_to_string (fn, term_out)
...

Tested on x86_64-linux.

1 files changed, 9 insertions, 3 deletions

diff --git a/gdb/gdbcmd.h b/gdb/gdbcmd.h
index 59afb0a..39f5ede 100644
--- a/gdb/gdbcmd.h
+++ b/gdb/gdbcmd.h
@@ -42,7 +42,8 @@ extern void execute_fn_to_ui_file (struct ui_file *file, std::function<void(void
    (e.g. with styling).  When TERM_OUT is false raw output will be collected
    (e.g. no styling).  */
 
-extern std::string execute_fn_to_string (std::function<void(void)> fn, bool term_out);
+extern void execute_fn_to_string (std::string &res,
+				  std::function<void(void)> fn, bool term_out);
 
 /* As execute_fn_to_ui_file, but run execute_command for P and FROM_TTY.  */
 
@@ -51,8 +52,13 @@ extern void execute_command_to_ui_file (struct ui_file *file,
 
 /* As execute_fn_to_string, but run execute_command for P and FROM_TTY.  */
 
-extern std::string execute_command_to_string (const char *p, int from_tty,
-					      bool term_out);
+extern void execute_command_to_string (std::string &res, const char *p,
+				       int from_tty, bool term_out);
+
+/* As execute_command_to_string, but ignore resulting string.  */
+
+extern void execute_command_to_string (const char *p,
+				       int from_tty, bool term_out);
 
 extern void print_command_line (struct command_line *, unsigned int,
 				struct ui_file *);