[FFmpeg-devel] [PATCH]lavf/mlv: Fix an snprintf() truncation

[Clément Bœsch]

On Tue, May 09, 2017 at 03:32:36PM +0200, Carl Eugen Hoyos wrote:
> Hi!
> 
> Attached patch fixes a warning when compiling with gcc 7:
> libavformat/mlvdec.c: In function ‘read_header’:
> libavformat/mlvdec.c:353:58: warning: ‘snprintf’ output may be truncated 
> before the last format character [-Wformat-truncation=]
>              snprintf(filename + strlen(filename) - 2, 3, "%02d", i);
> 
> Please comment, Carl Eugen

> From f56bf75b2b8b99cbbe99da8d2e33e46bf50be92d Mon Sep 17 00:00:00 2001
> From: Carl Eugen Hoyos <cehoyos at ag.or.at>
> Date: Tue, 9 May 2017 15:27:44 +0200
> Subject: [PATCH] lavf/mlvdec: Avoid snprintf() output truncation.
> 
> Fixes a gcc warning:
> 'snprintf' output may be truncated before the last format character
> ---
>  libavformat/mlvdec.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavformat/mlvdec.c b/libavformat/mlvdec.c
> index 319cd26..372acbe 100644
> --- a/libavformat/mlvdec.c
> +++ b/libavformat/mlvdec.c
> @@ -349,7 +349,7 @@ static int read_header(AVFormatContext *avctx)
>          if (!filename)
>              return AVERROR(ENOMEM);
>  
> -        for (i = 0; i < 100; i++) {
> +        for (i = 0; i < 99; i++) {
>              snprintf(filename + strlen(filename) - 2, 3, "%02d", i);
>              if (avctx->io_open(avctx, &mlv->pb[i], filename, AVIO_FLAG_READ, NULL) < 0)
>                  break;

can you explain? The current loop is not supposed to ever reach 100.

-- 
Clément B.
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