1 files changed, 18 insertions, 8 deletions

diff --git a/zlib.h b/zlib.h
index 2881da7..595e3cf 100644
--- a/zlib.h
+++ b/zlib.h
@@ -1239,13 +1239,14 @@ ZEXTERN uLong ZEXPORT zlibCompileFlags(void);
      21: FASTEST -- deflate algorithm with only one, lowest compression level
      22,23: 0 (reserved)
 
-    The sprintf variant used by gzprintf (zero is best):
+    The sprintf variant used by gzprintf (all zeros is best):
      24: 0 = vs*, 1 = s* -- 1 means limited to 20 arguments after the format
-     25: 0 = *nprintf, 1 = *printf -- 1 means gzprintf() not secure!
+     25: 0 = *nprintf, 1 = *printf -- 1 means gzprintf() is not secure!
      26: 0 = returns value, 1 = void -- 1 means inferred string length returned
+     27: 0 = gzprintf() present, 1 = not -- 1 means gzprintf() returns an error
 
     Remainder:
-     27-31: 0 (reserved)
+     28-31: 0 (reserved)
  */
 
 #ifndef Z_SOLO
@@ -1527,7 +1528,11 @@ ZEXTERN z_size_t ZEXPORT gzfwrite(voidpc buf, z_size_t size,
    gzwrite() instead.
 */
 
+#if defined(STDC) || defined(Z_HAVE_STDARG_H)
 ZEXTERN int ZEXPORTVA gzprintf(gzFile file, const char *format, ...);
+#else
+ZEXTERN int ZEXPORTVA gzprintf();
+#endif
 /*
      Convert, format, compress, and write the arguments (...) to file under
    control of the string format, as in fprintf.  gzprintf returns the number of
@@ -1535,11 +1540,16 @@ ZEXTERN int ZEXPORTVA gzprintf(gzFile file, const char *format, ...);
    of error.  The number of uncompressed bytes written is limited to 8191, or
    one less than the buffer size given to gzbuffer().  The caller should assure
    that this limit is not exceeded.  If it is exceeded, then gzprintf() will
-   return an error (0) with nothing written.  In this case, there may also be a
-   buffer overflow with unpredictable consequences, which is possible only if
-   zlib was compiled with the insecure functions sprintf() or vsprintf(),
-   because the secure snprintf() or vsnprintf() functions were not available.
-   This can be determined using zlibCompileFlags().
+   return an error (0) with nothing written.
+
+     In that last case, there may also be a buffer overflow with unpredictable
+   consequences, which is possible only if zlib was compiled with the insecure
+   functions sprintf() or vsprintf(), because the secure snprintf() and
+   vsnprintf() functions were not available. That would only be the case for
+   a non-ANSI C compiler. zlib may have been built without gzprintf() because
+   secure functions were not available and having gzprintf() be insecure was
+   not an option, in which case, gzprintf() returns Z_STREAM_ERROR. All of
+   these possibilities can be determined using zlibCompileFlags().
 
      If a Z_BUF_ERROR is returned, then nothing was written due to a stall on
    the non-blocking write destination.