The previous implementation was unnecessarily complex. Get rid of the loops,
let vsnprintf() tell us directly how much storage we need and allocate that. A
second pass writes the actual string. Also add a va_end() that was missing.
This should be much faster for large strings and less wasteful for small ones.
A quirk that has been retained is that some callers patch in a newline at the
end of the returned string and depend on alloc_vprintf to allocate at least
one byte extra.
Signed-off-by: Andreas Fritiofson <andreas.fritiof...@gmail.com>
---
This time without the copy/paste error. Thanks Zach for spotting it.
---
src/helper/log.c | 43 ++++++++++++++++---------------------------
1 files changed, 16 insertions(+), 27 deletions(-)
diff --git a/src/helper/log.c b/src/helper/log.c
index caaed42..2dcf7bb 100644
--- a/src/helper/log.c
+++ b/src/helper/log.c
@@ -395,37 +395,26 @@ int log_remove_callback(log_callback_fn fn, void *priv)
/* return allocated string w/printf() result */
char *alloc_vprintf(const char *fmt, va_list ap)
{
- /* no buffer at the beginning, force realloc to do the job */
- char *string = NULL;
-
- /* start with buffer size suitable for typical messages */
- int size = 128;
-
- for (;;)
- {
- char *t = string;
- va_list ap_copy;
- int ret;
- string = realloc(string, size);
- if (string == NULL)
- {
- if (t != NULL)
- free(t);
- return NULL;
- }
+ va_list ap_copy;
+ int len;
+ char *string;
- va_copy(ap_copy, ap);
+ /* determine the length of the buffer needed */
+ va_copy(ap_copy, ap);
+ len = vsnprintf(NULL, 0, fmt, ap_copy);
+ va_end(ap_copy);
- ret = vsnprintf(string, size, fmt, ap_copy);
- /* NB! The result of the vsnprintf() might be an *EMPTY*
string! */
- if ((ret >= 0) && ((ret + 1) < size))
- break;
+ /* allocate and make room for terminating zero. */
+ /* FIXME: The old version always allocated at least one byte extra and
+ * other code depend on that. They should be probably be fixed, but for
+ * now reserve the extra byte. */
+ string = malloc(len + 2);
+ if (string == NULL)
+ return NULL;
- /* there was just enough or not enough space, allocate more in
the next round */
- size *= 2; /* double the buffer size */
- }
+ /* do the real work */
+ vsnprintf(string, len + 1, fmt, ap);
- /* the returned buffer is by principle guaranteed to be at least one
character longer */
return string;
}
--
1.6.3.3
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