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.

1 files changed, 12 insertions, 5 deletions

diff --git a/gdb/gmp-utils.c b/gdb/gmp-utils.c
index db92e57..44fe156 100644
--- a/gdb/gmp-utils.c
+++ b/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.  */