Re: [RFA 2/3] New function cli-utils.c:extract_arg_const

[Pedro Alves <palves@redhat.com>]

On 11/11/2013 06:37 AM, Joel Brobecker wrote:
> Hello,
> 
> This function provides the exact same functionality as extract_arg,
> except that it takes a "const char**" instead of a "char **". This
> will be useful in the context of my next patch.
> 
> gdb/ChangeLog:
> 
>         * cli/cli-utils.h (extract_arg_const): Add declaration.
>         * cli/cli-utils.c (extract_arg_const): New function.
> 
> Tested on x86_64-linux. OK to push?

Instead of essentially duplicating the code, how about we reimplement
one on top of the other?  See below.  It compiles, but it's otherwise
untested.

-----------------
 gdb/cli/cli-utils.c |   25 +++++++++++++++++--------
 gdb/cli/cli-utils.h |    7 +++++++
 2 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/gdb/cli/cli-utils.c b/gdb/cli/cli-utils.c
index f74e6b1..316cf4f 100644
--- a/gdb/cli/cli-utils.c
+++ b/gdb/cli/cli-utils.c
@@ -261,30 +261,39 @@ remove_trailing_whitespace (const char *start, char *s)
 /* See documentation in cli-utils.h.  */
 
 char *
-extract_arg (char **arg)
+extract_arg_const (const char **arg)
 {
-  char *result, *copy;
+  const char *result;
 
   if (!*arg)
     return NULL;
 
   /* Find the start of the argument.  */
-  *arg = skip_spaces (*arg);
+  *arg = skip_spaces_const (*arg);
   if (!**arg)
     return NULL;
   result = *arg;
 
   /* Find the end of the argument.  */
-  *arg = skip_to_space (*arg + 1);
+  *arg = skip_to_space_const (*arg + 1);
 
   if (result == *arg)
     return NULL;
 
-  copy = xmalloc (*arg - result + 1);
-  memcpy (copy, result, *arg - result);
-  copy[*arg - result] = '\0';
+  return savestring (result, *arg - result);
+}
+
+/* See documentation in cli-utils.h.  */
+
+char *
+extract_arg (char **arg)
+{
+  const char *arg_const = *arg;
+  char *result;
 
-  return copy;
+  result = extract_arg_const (&arg_const);
+  *arg += arg_const - *arg;
+  return result;
 }
 
 /* See documentation in cli-utils.h.  */
diff --git a/gdb/cli/cli-utils.h b/gdb/cli/cli-utils.h
index 152fb89..ebae2d2 100644
--- a/gdb/cli/cli-utils.h
+++ b/gdb/cli/cli-utils.h
@@ -118,6 +118,13 @@ extern char *remove_trailing_whitespace (const char *start, char *s);
 
 extern char *extract_arg (char **arg);
 
+/* A const-correct version of "extract_arg".
+
+   Since the returned value is xmalloc'd, it eventually needs to be
+   xfree'ed, which prevents us from making it const as well.  */
+
+extern char *extract_arg_const (const char **arg);
+
 /* A helper function that looks for an argument at the start of a
    string.  The argument must also either be at the end of the string,
    or be followed by whitespace.  Returns 1 if it finds the argument,