memmove

可以将文章内容翻译成中文,广告屏蔽插件可能会导致该功能失效(如失效，请关闭广告屏蔽插件后再试): 问题: I understand that memmove and memcpy difference is that memmove handles the memory overlap case. I have checked the implementation in libgcc and got this article [memcpy performance] from the intel website. In libgcc, the memmove is similar to memcpy , both just go though one byte and byte, so the performance should be almost same even after optimization. Someone has measured this and got this article memcopy, memmove, and Speed over Safety . Even I don't think the memmove can be faster than memcpy , but there should be no big difference at

After reading the following about memcpy() , I proceeded to read about memmove() : To avoid overflows, the size of the arrays pointed by both the destination and source parameters, shall be at least num bytes, and should not overlap (for overlapping memory blocks, memmove is a safer approach). (LINK) And after checking the program used to illustrate the working of memmove() I decided to tweak it by using memcpy() instead to see how different is the output.To my surprise,they are the same even if it's a case of overlapping memory blocks.Here is the program and the output,and I have proceeded to

Can some one help me to understand how memmove is implemented in C. I have only one special condition right ? if((src<dst)&&((src+sz) > dst)) copy from the back Also does it depend on the way stack grows ? Mathematically, you don't have to worry about whether they overlap at all. If src is less than dst , just copy from the end. If src is greater than dst , just copy from the beginning. If src and dst are equal, just exit straight away. That's because your cases are one of: 1) <-----s-----> start at end of s <-----d-----> 2) <-----s-----> start at end of s <-----d-----> 3) <-----s-----> no

Do I need to treat cases when I actully have nothing to move/copy with memmove() / memcpy() as edge cases int numberOfBytes = ... if( numberOfBytes != 0 ) { memmove( dest, source, numberOfBytes ); } or should I just call the function without checking int numberOfBytes = ... memmove( dest, source, numberOfBytes ); Is the check in the former snippet necessary? From the C99 standard (7.21.1/2): Where an argument declared as size_t n specifies the length of the array for a function, n can have the value zero on a call to that function. Unless explicitly stated otherwise in the description of a

What is the difference between memmove and memcpy ? Which one do you usually use and how? bdonlan With memcpy , the destination cannot overlap the source at all. With memmove it can. This means that memmove might be very slightly slower than memcpy , as it cannot make the same assumptions. For example, memcpy might always copy addresses from low to high. If the destination overlaps after the source, this means some addresses will be overwritten before copied. memmove would detect this and copy in the other direction - from high to low - in this case. However, checking this and switching to

I am trying to understand the difference between memcpy() and memmove() , and I have read the text that memcpy() doesn't take care of the overlapping source and destination whereas memmove() does. However, when I execute these two functions on overlapping memory blocks, they both give the same result. For instance, take the following MSDN example on the memmove() help page:- Is there a better example to understand the drawbacks of memcpy and how memmove solves it? // crt_memcpy.c // Illustrate overlapping copy: memmove always handles it correctly; memcpy may handle // it correctly. #include