What is the underlying principle of the implementation …

The memcpy function is a memory copy function in the C++ standard library, used to copy data of a specified length from a source address to a destination address.

The underlying implementation principle of memcpy is to copy data by directly replicating bytes in the memory. The specific steps are as follows:

1. Firstly, check if the target address and source address overlap. In the event of overlap, the specific copying strategy will be determined based on the memory region’s position and copy direction.
2. If the destination address and the source address do not overlap, or if they overlap but the copying direction is from the source address to the destination address in increasing order, then one safe and efficient way to copy is to copy byte by byte. This method can take advantage of modern processor features such as byte alignment, pipelines, and caches to improve copying efficiency.
3. If the target address overlaps with the source address and the copying direction is from the target address to the source address in an increasing manner, a more complex method of copying is needed, which involves copying byte by byte in reverse. This is because if copied in an increasing manner, it would result in the data at the target address being overwritten, leading to data corruption. Reverse copying involves starting from the end to prevent data from being overwritten.

In general, the underlying principle behind memcpy is to efficiently copy data by copying memory bytes one by one. The specific copying strategy depends on the relationship between the destination and source addresses, as well as the direction of the copy.