I am wondering how can I convert std::vector<vector>
to void*
, for example:
std::vector<ColorData> pixels_ (w*h, background_color);
Now I want to convert pixels_
to void*
so that I can memcpy
the pixels_
.
memcpy ((void*)destinationBuffer->pixels_, (void*)sourceBuffer->pixels_, \
sizeof(ColorData)*destinationBuffer->width_*destinationBuffer->height_);
But when I run this code, I get an error which says:
invalid cast from type 'std::vector<image_tools::ColorData>' to type 'void*'
How can I convert std::vector<vector>
to void*
?
To transform your vector into a void*
type, there are two options:
(void*)&pixels_[0]
( !empty()
check is recommended) static_cast<void*>(pixels_.data())
However, if you want to copy the elements, go straight with STL functions:
They are type safe, your code looks much cleaner and the performance will be on par most of the times. Also, unlike std::memcpy
, it also supports non-trivially copyable types (for example std::shared_ptr
).
Remember:
We should forget about small efficiencies, say about 97% of the time: premature optimization is the root of all evil. Yet we should not pass up our opportunities in that critical 3%
Update: since C++17 you can also use std::data
, which will work for any container using contiguous memory storage (eg std::vector
, std::string
, std::array
).
ColorData* buffer = std::data(pixels_);
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