Error Memcpy Called With Overlapping Regions
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Memcpy Overlapping Memory
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Memmove Example In C
just like you, helping each other. Join them; it only takes a minute: Sign up memcpy() vs memmove() up vote 103 down vote favorite 40 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.
Memmove Overlap
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
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What Is The Difference Between The Functions Memmove() And Memcpy()
Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community memmove_s of 4.7 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up memcpy of overlapping buffers up vote 8 down vote favorite I ran into strange behavior when http://stackoverflow.com/questions/4415910/memcpy-vs-memmove using the Aztec linear system solver library. Using valgrind, I found out that this library does a memcpy on overlapping buffers. Specification says that behavior of memcpy on overlapping buffers is not defined. It turns out that memcpy on many machines has the same behavior as if you would do it with a for loop and therefore you can safely copy from a higher source to a lower destination: for(int i http://stackoverflow.com/questions/25629736/memcpy-of-overlapping-buffers = 0; i < len; i ++) dest[i] = source[i]; BUT on our large cluster, memcpy of overlapping buffers has a different behavior which leads to problems. Now I wonder whether the overlapping memcpy in the library is normal or just caused by another bug in my code. Since the library is widely used I assume that the memcpy issue should have been discovered earlier. On the other hand, it's still possible that the vast majority of the memcpy implementations behave like the for loop and therefore nobody ever encountered this problem. Can anyone tell me about his experiences with overlapping memcpy on various machines? Which part of my computer system does actually provide memcpy? I'd like to point out that question is about the practical experience with various implementations, not about what the specification says. c++ c memcpy share|improve this question asked Sep 2 '14 at 18:14 Michael 2,1721130 Please provide a minimal example, so that we can reproduce your issue and let you know if the bug is in the library or in your code. –OmnipotentEntity Sep 2 '14 at 18:24 I've never understood this issue with memcpy. Surely, it's only one compare to find out if you need to copy from the top or botto
[x] Format For Printing -XML -Clone This Bug -Last Comment First Last Prev Next https://bugzilla.redhat.com/show_bug.cgi?id=691336 This bug is not in your last search results. http://www.java-samples.com/showtutorial.php?tutorialid=591 Bug691336 - memcpy acts randomly (and differently) with overlapping areas Summary: memcpy acts randomly (and differently) with overlapping areas Status: CLOSED NOTABUG Aliases: None Product: Fedora Classification: Fedora Component: glibc (Show other bugs) Sub Component: --- Version: 14 Hardware: Unspecified Unspecified Priority unspecified in c Severity unspecified TargetMilestone: --- TargetRelease: --- Assigned To: Andreas Schwab QA Contact: Fedora Extras Quality Assurance Docs Contact: URL: Whiteboard: Keywords: Reopened Depends On: Blocks: Show dependency tree /graph Reported: 2011-03-28 05:54 EDT by Felipe Contreras Modified: 2011-03-28 12:53 EDT (History) CC List: 8 users (show) alexander.hunt2005 jakub mail2benny martin mathieu-acct rich memcpy and memmove schwab tmraz See Also: Fixed In Version: Doc Type: Bug Fix Doc Text: Story Points: --- Clone Of: Environment: Last Closed: 2011-03-28 08:03:27 EDT Type: --- Regression: --- Mount Type: --- Documentation: --- CRM: Verified Versions: Category: --- oVirt Team: --- RHEL 7.3 requirements from Atomic Host: Cloudforms Team: --- Attachments (Terms of Use) Add an attachment (proposed patch, testcase, etc.) Groups: None (edit) Description Felipe Contreras 2011-03-28 05:54:32 EDT Description of problem: glibc changed the behavior of memcpy which used to work like memmove, but now it breaks certain use-cases. Considering it's impossible to check all the millions of lines of code possibly affected, and that produces _zero_ gain, it's hard to tout in favor of this change. Additional info: Here's the upstream bug: http://sources.redhat.com/bugzilla/show_bug.cgi?id=12518 In the words of Linus Torvalds: I realize that it's technically "undefined", but the behavior has changed, and in the process broken existing binaries. It's a common bug to use memcpy() instead o
memmove() in C By: Emiley J Emailed: 1505 times Printed: 1827 times Latest comments By: rohit kumar - how this program is work By: Kirti - Hi..thx for the hadoop inBy: Spijker - I have altered the code aBy: ali mohammed - why we use the java in neBy: ali mohammed - why we use the java in neBy: mizhelle - when I exported the data By: raul - no output as well, i'm geBy: Rajesh - thanx very much...By: Suindu De - Suppose we are executing The memset() Function To set all the bytes in a block of memory to a particular value, use memset(). The function prototype is void * memset(void *dest, int c, size_t count); The argument dest points to the block of memory. c is the value to set, and count is the number of bytes, starting at dest, to be set. Note that while c is a type int, it is treated as a type char. In other words, only the low-order byte is used, and you can specify values of c only in the range 0 through 255. Use memset() to initialize a block of memory to a specified value. Because this function can use only a type char as the initialization value, it is not useful for working with blocks of data types other than type char, except when you want to initialize to 0. In other words, it wouldn't be efficient to use memset() to initialize an array of type int to the value 99, but you could initialize all array elements to the value 0. memset() will be demonstrated in program below. The memcpy() Function memcpy() copies bytes of data between memory blocks, sometimes called buffers. This function doesn't care about the type of data being copied--it simply makes an exact byte-for-byte copy. The function prototype is void *memcpy(void *dest, void *src, size_t count); The arguments dest and src point to the destination and source memory blocks, respectively. count specifies the number of bytes to be copied. The return value is dest. If the two blocks of memory overlap, the function might not operate properly--some of the data in src might be overwritten before being copied. Use the memmove() function, discussed next, to handle overlapping memory blocks. memcpy() will be demonstrated in program below. The memmove() Function memmove() is very much like memcpy(), copying a specified number of bytes from one memory block to another. It's more flexible, however, because it can handle overlapping memory blocks properly. Because memmove() can do everything memcpy() can do with the added flexibility of dealing with overlapping blocks, you rarely, if ever, should have a reason to u