[FFmpeg-devel] [PATCH 2/2] compat/vsnprintf: return number of bytes required on truncation.

[Derek Buitenhuis]

From: "Ronald S. Bultje" <rsbultje at gmail.com>

This conforms to C99, but requires Windows >= XP.
---
 compat/msvcrt/snprintf.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/compat/msvcrt/snprintf.c b/compat/msvcrt/snprintf.c
index 36f6dd1..244e1e9 100644
--- a/compat/msvcrt/snprintf.c
+++ b/compat/msvcrt/snprintf.c
@@ -43,9 +43,10 @@ int avpriv_vsnprintf(char *s, size_t n, const char *fmt,
                      va_list ap)
 {
     int ret;
+    va_list ap_copy;
 
     if (n == 0)
-        return 0;
+        return _vscprintf(fmt, ap);
     else if (n > INT_MAX)
         return AVERROR(EOVERFLOW);
 
@@ -57,8 +58,11 @@ int avpriv_vsnprintf(char *s, size_t n, const char *fmt,
      * See http://msdn.microsoft.com/en-us/library/1kt27hek(v=vs.80).aspx */
     memset(s, 0, n);
     ret = _vsnprintf(s, n - 1, fmt, ap);
-    if (ret == -1)
-        ret = n;
+    if (ret == -1) {
+        va_copy(ap_copy, ap);
+        ret = _vscprintf(fmt, ap);
+        va_end(ap_copy);
+    }
 
     return ret;
 }
-- 
1.7.9.5