问题
I am wondering how can I convert std::vector to void*, for example,
std::vector<ColorData> piexls_ (w*h, background_color);
Now I want to convert piexls_ 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 got the error says that invalid cast from type ‘std::vector<image_tools::ColorData>’ to type ‘void*’
How can I convert std::vector to void*. Thank you so much!
回答1:
To transform your vector into a void* type, there are two options:
- Pre C++11:
(void*)&pixels_[0](!empty()check is recommended) - Since C++11:
static_cast<void*>(pixels_.data())
However, if you want to copy the elements, go straight with STL functions:
- std::copy
- std::uninitialized_copy
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%
See TriviallyCopyable
Update: since C++17 you can also use std::data, which will work for any container using contiguous memory storage (e.g. std::vector, std::string, std::array).
ColorData* buffer = std::data(pixels_);
来源：https://stackoverflow.com/questions/40594494/how-to-convert-stdvectorvector-to-void