[FFmpeg-devel] [PATCH] gdigrab: Fix hwnd parameter issues

[Stefano Sabatini]

On date Monday 2023-12-18 19:05:17 -0300, James Almer wrote:
> On 12/18/2023 5:54 AM, Martin Storsjö wrote:
> > Converting from an integer to HWND (which is a pointer) requires
> > an explicit cast, otherwise Clang errors out like this:
> > 
> >      src/libavdevice/gdigrab.c:280:14: error: incompatible integer to pointer conversion assigning to 'HWND' (aka 'struct HWND__ *') from 'long' [-Wint-conversion]
> >        280 |         hwnd = strtol(name, &p, 0);
> >            |              ^ ~~~~~~~~~~~~~~~~~~~
> > 
> > (With GCC and MSVC, this was a mere warning, but with recent Clang,
> > this is an error.)
> > 
> > After adding a cast, all compilers also warn something like this:
> > 
> >      src/libavdevice/gdigrab.c:280:16: warning: cast to 'HWND' (aka 'struct HWND__ *') from smaller integer type 'long' [-Wint-to-pointer-cast]
> >        280 |         hwnd = (HWND) strtol(name, &p, 0);
> >            |                ^~~~~~~~~~~~~~~~~~~~~~~~~~
> > 
> > On Windows, long types are 32 bit, so to get a usable pointer, we
> > need to use long long. And interpret it as unsigned long long
> > while at it - i.e. using strtoull.
> > 
> > Finally, right above it, the code triggered the following warning:
> > 
> >      src/libavdevice/gdigrab.c:278:15: warning: mixing declarations and code is incompatible with standards before C99 [-Wdeclaration-after-statement]
> >        278 |         char *p;
> >            |               ^
> > ---
> >   libavdevice/gdigrab.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/libavdevice/gdigrab.c b/libavdevice/gdigrab.c
> > index 41ef370f2b..b2858ecd89 100644
> > --- a/libavdevice/gdigrab.c
> > +++ b/libavdevice/gdigrab.c
> > @@ -274,10 +274,10 @@ gdigrab_read_header(AVFormatContext *s1)
> >       } else if (!strcmp(filename, "desktop")) {
> >           hwnd = NULL;
> >       } else if (!strncmp(filename, "hwnd=", 5)) {
> > -        name = filename + 5;
> >           char *p;
> > +        name = filename + 5;
> > -        hwnd = strtol(name, &p, 0);
> > +        hwnd = (HWND) strtoull(name, &p, 0);
> >           if (p == NULL || p == name || p[0] == '\0')
> >           {
> 
> Should be ok.

Also LGTM, thanks.