Note the use of gzungetc() to run a deferred seek while reading.

1 files changed, 5 insertions, 0 deletions

diff --git a/zlib.h b/zlib.h
index c055ecb..1a57127 100644
--- a/zlib.h
+++ b/zlib.h
@@ -1549,6 +1549,11 @@ ZEXTERN int ZEXPORT gzungetc(int c, gzFile file);
    output buffer size of pushed characters is allowed.  (See gzbuffer above.)
    The pushed character will be discarded if the stream is repositioned with
    gzseek() or gzrewind().
+
+     gzungetc(-1, file) will force any pending seek to execute. Then gztell()
+   will report the position, even if the requested seek reached end of file.
+   This can be used to determine the number of uncompressed bytes in a gzip
+   file without having to read it into a buffer.
 */
 
 ZEXTERN int ZEXPORT gzflush(gzFile file, int flush);