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

[Martin Storsjö]

On Mon, 18 Dec 2023, Stefano Sabatini wrote:

> 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.

Pushed now, thanks!

// Martin