change and rename gmp_string_asprintf to return an std::string

This was suggested by Simon during a code review of this package upstream.
The upside is that this makes the function's API more natural and C++.
The downside is an extra malloc, which might be the reason why we went
for using a unique_xmalloc_ptr in the first place. Since this function
is not expected to be called frequently, the API improvement might be
worth the performance impact.

gdb/ChangeLog:

        * gmp-utils.h (gmp_string_printf): Rename from gmp_string_asprintf.
        Change return type to std::string. Update all callers.
        * gmp-utils.c (gmp_string_printf): Likewise.

gdb/ChangeLog

@@ -1,3 +1,9 @@
+2020-11-24  Joel Brobecker  <brobecker@adacore.com>
+
+	* gmp-utils.h (gmp_string_printf): Rename from gmp_string_asprintf.
+	Change return type to std::string. Update all callers.
+	* gmp-utils.c (gmp_string_printf): Likewise.
+
 2020-11-24  Joel Brobecker  <brobecker@adacore.com>
 
 	* unittests/gmp-utils-selftests.c (write_fp_test): Use mpq_set_si

gdb/gdbtypes.c

@@ -4927,7 +4927,7 @@ static void
 print_fixed_point_type_info (struct type *type, int spaces)
 {
   printfi_filtered (spaces + 2, "scaling factor: %s\n",
-		    fixed_point_scaling_factor (type).str ().get ());
+		    fixed_point_scaling_factor (type).str ().c_str ());
 }
 
 static struct obstack dont_print_type_obstack;

gdb/gmp-utils.c

@@ -19,17 +19,24 @@
 
 /* See gmp-utils.h.  */
 
-gdb::unique_xmalloc_ptr<char>
-gmp_string_asprintf (const char *fmt, ...)
+std::string
+gmp_string_printf (const char *fmt, ...)
 {
   va_list vp;
-  char *buf;
 
   va_start (vp, fmt);
-  gmp_vasprintf (&buf, fmt, vp);
+  int size = gmp_vsnprintf (NULL, 0, fmt, vp);
   va_end (vp);
 
-  return gdb::unique_xmalloc_ptr<char> (buf);
+  std::string str (size, '\0');
+
+  /* C++11 and later guarantee std::string uses contiguous memory and
+     always includes the terminating '\0'.  */
+  va_start (vp, fmt);
+  gmp_vsprintf (&str[0], fmt, vp);
+  va_end (vp);
+
+  return str;
 }
 
 /* See gmp-utils.h.  */

gdb/gmp-utils.h

@@ -29,9 +29,9 @@
 #include <gmp.h>
 #include "gdbsupport/traits.h"
 
-/* Same as gmp_asprintf, but returning a convenient wrapper type.  */
+/* Same as gmp_asprintf, but returning an std::string.  */
 
-gdb::unique_xmalloc_ptr<char> gmp_string_asprintf (const char *fmt, ...);
+std::string gmp_string_printf (const char *fmt, ...);
 
 /* A class to make it easier to use GMP's mpz_t values within GDB.  */
 
@@ -110,8 +110,7 @@ struct gdb_mpz
 	      bool unsigned_p) const;
 
   /* Return a string containing VAL.  */
-  gdb::unique_xmalloc_ptr<char> str () const
-  { return gmp_string_asprintf ("%Zd", val); }
+  std::string str () const { return gmp_string_printf ("%Zd", val); }
 
   /* The destructor.  */
   ~gdb_mpz () { mpz_clear (val); }
@@ -163,8 +162,7 @@ struct gdb_mpq
   }
 
   /* Return a string representing VAL as "<numerator> / <denominator>".  */
-  gdb::unique_xmalloc_ptr<char> str () const
-  { return gmp_string_asprintf ("%Qd", val); }
+  std::string str () const { return gmp_string_printf ("%Qd", val); }
 
   /* Return VAL rounded to the nearest integer.  */
   gdb_mpz get_rounded () const;

gdb/typeprint.c

@@ -667,11 +667,10 @@ print_type_scalar (struct type *type, LONGEST val, struct ui_file *stream)
 void
 print_type_fixed_point (struct type *type, struct ui_file *stream)
 {
-  gdb::unique_xmalloc_ptr<char> small_img
-    = fixed_point_scaling_factor (type).str ();
+  std::string small_img = fixed_point_scaling_factor (type).str ();
 
   fprintf_filtered (stream, "%s-byte fixed point (small = %s)",
-		    pulongest (TYPE_LENGTH (type)), small_img.get ());
+		    pulongest (TYPE_LENGTH (type)), small_img.c_str ());
 }
 
 /* Dump details of a type specified either directly or indirectly.

gdb/valprint.c

@@ -814,8 +814,8 @@ generic_val_print_fixed_point (struct value *val, struct ui_file *stream,
 			  fixed_point_scaling_factor (type));
 
       const char *fmt = TYPE_LENGTH (type) < 4 ? "%.11Fg" : "%.17Fg";
-      gdb::unique_xmalloc_ptr<char> str = gmp_string_asprintf (fmt, f.val);
-      fprintf_filtered (stream, "%s", str.get ());
+      std::string str = gmp_string_printf (fmt, f.val);
+      fprintf_filtered (stream, "%s", str.c_str ());
     }
 }