Can memcpy overlap?
Can memcpy overlap?
The memory in memcpy cannot overlap or you risk undefined behaviour, while the memory in memmove can overlap. Some implementations of memcpy might still work for overlapping inputs but you cannot count of that behaviour.
What is the difference between memcpy and memmove?
Answer: memcpy() function is is used to copy a specified number of bytes from one memory to another. memmove() function is used to copy a specified number of bytes from one memory to another or to overlap on same memory.
Will memcpy overwrite?
3 Answers. You need to change the destination pointer each time you call memcpy . memcpy replaces memory, it does not append. You need to increment the destination address everytime you use memcpy so that it places it in subsequent memory, instead of overwriting the same string each time.
How can I improve my memcpy?
Optimizing Memcpy improves speed
- Three basic memcpy() algorithms. The simplest memory-transfer algorithm just reads one byte at a time and writes that byte before reading the next.
- Block size.
- Data alignment.
- Caching.
- Write policy.
- Special situations.
- Optimize away.
Why is memcpy slow?
I also had some code that I really needed to speed up, and memcpy is slow because it has too many unnecessary checks. For example, it checks to see if the destination and source memory blocks overlap and if it should start copying from the back of the block rather than the front.
Is there anything faster than memcpy?
On Ryzen 1800X with single memory channel filled completely (2 slots, 16 GB DDR4 in each), the following code is 1.56 times faster than memcpy() on MSVC++2017 compiler. If you fill both memory channels with 2 DDR4 modules, i.e. you have all 4 DDR4 slots busy, you may get further 2 times faster memory copying.
Can memcpy be interrupted?
Yes – but if you are using memcpy to copy a function from flash to RAM and that function happens to be used by the interrupt it would not work since it isn’t fully copied over. Same if you are using it to copy data that the interrupt then uses – it would be in mid copy.
How does memcpy work in C?
The memcpy function is used to copy a block of data from a source address to a destination address. Below is its prototype. The idea is to simply typecast given addresses to char * (char takes 1 byte). Then one by one copy data from source to destination.
What are the disadvantages of memcpy()?
memcpy() leads to problems when source and destination addresses overlap as memcpy() simply copies data one by one from one location to another. For example consider below program. // Sample program to show that memcpy() can loose data.
Is it possible to avoid double copies of a memmove?
Double copies should be avoided unless if it is really impossible. In this case though it is easily possible to avoid double copies by picking a direction of copy. In fact this is what the memmove () library function does.
