On 21/04/2021 11:19, Rosen Penev wrote:
>
>> On Apr 21, 2021, at 01:23, Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>>
>>> On 21/04/2021 09:20, Rosen Penev wrote:
>>> The array has a nullptr and 0 member for some reason. Remove and convert
>>> loop to a for range one.
>>>
>>> Signed-off-by: Rosen Penev <rosenp@xxxxxxxxx>
>>> ---
>>> utils/common/v4l2-info.cpp | 33 +++++++++++++++------------------
>>> 1 file changed, 15 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/utils/common/v4l2-info.cpp b/utils/common/v4l2-info.cpp
>>> index cb3cb91f7..0359cf137 100644
>>> --- a/utils/common/v4l2-info.cpp
>>> +++ b/utils/common/v4l2-info.cpp
>>> @@ -3,6 +3,8 @@
>>> * Copyright 2018 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
>>> */
>>>
>>> +#include <array>
>>> +
>>> #include <v4l2-info.h>
>>>
>>> static std::string num2s(unsigned num, bool is_hex = true)
>>> @@ -411,21 +413,20 @@ std::string mbus2s(unsigned flags, bool is_hsv)
>>> return flags2s(flags, mbus_ycbcr_def);
>>> }
>>>
>>> -static const flag_def selection_targets_def[] = {
>>> - { V4L2_SEL_TGT_CROP_ACTIVE, "crop" },
>>> - { V4L2_SEL_TGT_CROP_DEFAULT, "crop_default" },
>>> - { V4L2_SEL_TGT_CROP_BOUNDS, "crop_bounds" },
>>> - { V4L2_SEL_TGT_COMPOSE_ACTIVE, "compose" },
>>> - { V4L2_SEL_TGT_COMPOSE_DEFAULT, "compose_default" },
>>> - { V4L2_SEL_TGT_COMPOSE_BOUNDS, "compose_bounds" },
>>> - { V4L2_SEL_TGT_COMPOSE_PADDED, "compose_padded" },
>>> - { V4L2_SEL_TGT_NATIVE_SIZE, "native_size" },
>>> - { 0, nullptr }
>>
>> The idea of having this sentinel is that this makes it easy to add new
>> entries without having to update the array size.
> Not following this. I assume it’s some C feature.
Standard programming techique:
https://en.wikipedia.org/wiki/Sentinel_value#:~:text=In%20computer%20programming%2C%20a%20sentinel,a%20loop%20or%20recursive%20algorithm.
>>
>>> +static constexpr std::array<flag_def, 8> selection_targets_def{
>>
>> Something you need to do here, adding a new flag means updating the size.
> I assume this is a small issue. It’s an immediate compile error anyway.
Not if the size is larger that the number of initializers. That would leave
zeroed elements at the end.
>>
>> New flags are added regularly, so keeping that robust is a good idea IMHO.
>>
>> If it were possible to write:
>>
>> static constexpr std::array<flag_def> selection_targets_def{
>>
>> i.e. without an explicit size, then this would make sense, but C++
>> doesn't allow this. And std::vector allocates the data on the heap,
>> which is less efficient as well.
> But this is possible. With C++17 :). That would necessitate a minimum of GCC6 though.
How is that done in C++17? I didn't find anything about that.
Regards,
Hans
>>
>> Let's just keep using normal arrays in this case, they do the job
>> just fine. Just because you have a hammer, it doesn't mean everything
>> is now a nail :-)
>>
>> Regards,
>>
>> Hans
>>
>>> + flag_def{ V4L2_SEL_TGT_CROP_ACTIVE, "crop" },
>>> + flag_def{ V4L2_SEL_TGT_CROP_DEFAULT, "crop_default" },
>>> + flag_def{ V4L2_SEL_TGT_CROP_BOUNDS, "crop_bounds" },
>>> + flag_def{ V4L2_SEL_TGT_COMPOSE_ACTIVE, "compose" },
>>> + flag_def{ V4L2_SEL_TGT_COMPOSE_DEFAULT, "compose_default" },
>>> + flag_def{ V4L2_SEL_TGT_COMPOSE_BOUNDS, "compose_bounds" },
>>> + flag_def{ V4L2_SEL_TGT_COMPOSE_PADDED, "compose_padded" },
>>> + flag_def{ V4L2_SEL_TGT_NATIVE_SIZE, "native_size" },
>>> };
>>>
>>> bool valid_seltarget_at_idx(unsigned i)
>>> {
>>> - return i < sizeof(selection_targets_def) / sizeof(selection_targets_def[0]) - 1;
>>> + return i < selection_targets_def.size();
>>> }
>>>
>>> unsigned seltarget_at_idx(unsigned i)
>>> @@ -437,13 +438,9 @@ unsigned seltarget_at_idx(unsigned i)
>>>
>>> std::string seltarget2s(__u32 target)
>>> {
>>> - int i = 0;
>>> -
>>> - while (selection_targets_def[i].str != nullptr) {
>>> - if (selection_targets_def[i].flag == target)
>>> - return selection_targets_def[i].str;
>>> - i++;
>>> - }
>>> + for (const auto &def : selection_targets_def)
>>> + if (def.flag == target)
>>> + return def.str;
>>> return std::string("Unknown (") + num2s(target) + ")";
>>> }
>>>
>>>
>>
