Memcpy is ambiguous. Apr 25, 2024 · 文章浏览阅读1.

Memcpy is ambiguous What can be the problem here? Oct 24, 2022 · I'm 99% sure it's the same story as with C/C++: LLVM can replace large copies with calls to memcpy. Aug 7, 2020 · memcpy treats the arguments as though they were pointing to an array of the appropriate size of an unsigned narrow character type. Jan 25, 2021 · But once we understand the real rules, we recognize that this is still ambiguous. Topic archived. I suspect that this is because there are several functions defined with different paramete Feb 9, 2025 · std::memcpy is meant to be the fastest library routine for memory-to-memory copy. However, below code yields "error: reference to ‘negate’ is ambiguous". Edit: Jesse Beder is right in his comment to the question; the code doesn't make much sense, since _test is a type, not an object. 5k次。在集成OpenCV 3. It makes sense that gets(), strcpy and similar apis where the destination size is unclear. You don't even have to worry about overlapping memory as the behaviour of memcpy is undefined for overlapping memory. The code: IMAGE_DOS_HEADER iDOSh; memcpy(&amp;iDOSh, Sep 10, 2025 · 文章浏览阅读5k次。本文汇总了关于C++、C#、bat脚本、OpenCV及Keil的相关文章链接，旨在为读者提供一系列从基础知识到实践应用的学习资源。每篇文章的内容均经过调试验证，确保代码的有效性和实用性。 Mar 26, 2021 · The compiler might actually generate references to the memcpy function, even if your code doesn't explicitly call it. Is memmove() next? The memcpy () function shall copy n bytes from the object pointed to by s2 into the object pointed to by s1. Dec 22, 2017 · Here's original memcpy ends with zsh: abort, my version works ok. There was no direct usage of it in QPixmap, nor in QPixmapData, nor May 20, 2024 · C语言的 memcpy 函数不会在特定情况下正常工作，主要原因包括： 内存重叠、未初始化的指针、越界拷贝、对NULL指针的操作。在这些情况下， memcpy 可能导致不可预测的行为，包括数据损坏、程序崩溃等。在这些情况中，* 内存重叠 *\是一个常见问题，值得深入探讨。 内存重叠 发生时，源内存区域和 Jun 24, 2013 · Warning 669: Possible data overrun for function 'memcpy(void *, const void *, unsigned int)', argument 3 , 我制作了这段代码，因为 NUM_PEOPLE 可以更改为小于 TIME_PEOPLE，那么这个警告是如何发生的以及如何修复它？ Jan 22, 2020 · Using memcpy has fairly strict requirements on the types involved, or else it will do damage. If you absolutely need -nostdlib, I suppose you could define your own version of memcpy - if that's the only function the linker is complaining about. _test. May 15, 2009 · Duplicate: Memcpy () in secure programming? According to "Please Join me in welcoming memcpy () to the SDL Rogues Gallery" memcpy is being banned as unsafe. 9w次，点赞49次，收藏101次。背景描述：最近在一个qt项目中，数据传输部分多次使用了memcpy，程序编译没有一个警告或报错，但是一运行起来就不稳定了，有时甚至不能运行起来，有时跑起来能传输几条数据，有时又能接收到几十条数据，但最终程序都会异常crashed！！甚是恼火！排除 I don't think that functions such as memcpy_s really qualify as 'secure' replacements for memcpy, but either way they are equally applicable within pure 'C', there is not much that is 'C++' about them. Copying 2 ints is probably fast than calling a function (esp since it will copy the arguments anyway) and doing 8 copies Oct 4, 2012 · From your code, it appears that my_map_t::end() is static (otherwise you'd have to call it on an instance, e. Jun 3, 2010 · I have a problem my src pointer of memcpy is pointing wrong. Why is that? Aug 23, 2023 · 文章浏览阅读1. What if I change my compiler options / version for some other reason, and then find our that my elements aren't initialized to 0? I think one complier I had didn't even bother to 0 initialize statics. Example: Oct 26, 2010 · Re: memcpy not working properly It strikes me that, even if this did what you think it does, it would not do anything useful. Thanks. hpp file. I'm trying to figure out how to re-write this Rust code in C++ without using std::memcpy (why? because its fun): unsafe fn memcpy (dest: *mut u8, src… Not like that. Aug 9, 2019 · Updates: 2019-08-12 – Added note about using unions. My understanding is that it's not possible, but I agree that one can read the "Both dest and src may be either host or USM pointers" of the sycl::memcpy description in a little ambiguous maner. This article will explain how to use memcpy, when to Learn how firmware developers can resolve the 'memcpy' not declared issue in C++. Each of the available overloads is worse for at least one argument, therefore neither qualifies as a better match. 5k Views 1 Watching Oldest to Newest Sep 25, 2021 · The issue is in the call to std::memcpy: the arr argument will yield (by decay) a pointer to the first int [3] subarray so, according to one side of the discussion (led by Ted Lyngmo), when the memcpy function accesses data beyond the third element of that subarray, there is formally undefined behaviour (and the same would apply to the destination, arr_copy). If I call the functions explicitly with th Aug 14, 2024 · ！！ 下面在一起学习以下memcpy () memcpy指的是C和C++使用的内存拷贝函数，函数原型为: void *memcpy (void *destin, void *source, unsigned n)； 1 函数的功能是从源内存地址的起始位置开始拷贝若干个字节到目标内存地址中，即从源source中拷贝n个字节到目标destin中。 #include <cstring> void *memcpy( void *to, const void *from, size_t count ); The function memcpy () copies count characters from the array from to the array to. memcpy is not designed to be fast, it's designed to be portable. However I just don't get how it could be unsafe to use std::memcpy on a structure like point which is juste an array of floats also I tried to Jul 23, 2025 · C++ memcpy () function is a standard library function that is used to copy the specified number of bytes from one memory location to another memory location regardless of the type of data stored. h> Nov 25, 2016 · memcpy (void *destination, const void *source, size_t num); can be a very basic function - it just copies num bytes from source to destination (and returns the destination pointer). My program uses a 3rd party component name FlexCompress that has a function named memcpy listed in a machine generated header . Nov 5, 2020 · memcpy is the fastest library routine for memory-to-memory copy. The behavior of memcpy () is undefined if to and from overlap. Also, there will be issues in case of overlapping Mar 8, 2012 · Hi all! System information OS - Linux Debian 10 debian 4. When I Jun 30, 2025 · I think TableGen should emit these as enum classes instead of plain enums. Now it is working fine. I was wondering if anyone had a better way of doing the following for the Action::TurnOff: fn part2(instructions: &Vec<Instr>) -> usize { let mut grid = [[0; 1000]; 1000]; for instr in instructions { just playing devils advocate here, but isnt memcpy less ambiguous in this case. Static member functions cannot be const-qualified (the const-qualification of a member function applies to the this pointer; static member As all bounds-checked functions, memcpy_s is only guaranteed to be available if STDC_LIB_EXT1 is defined by the implementation and if the user defines STDC_WANT_LIB_EXT1 to the integer constant 1 before including string. I would bet that it will use appropriate assembly where applicable to do a block memory copy. No new replies allowed. My idea was that is the structures contains std::string / std::vector / other similar synamic object, then one would have to overide the serializing function. It is optimized for copying memory chunks in an efficient manner and it copies memory in a byte-by-byte format. If copying takes place between objects that overlap, the behaviour is undefined. In both cases explicitly deleted constructor/operator= indicates some intent not to allow the usual copying even if trivial. #include <string. Jun 20, 2011 · I am using some function templates in order to store data generically and per type. data,10); I am getting the following errors: warning: passing argument 2 of memcpy makes pointer from integer without a cast error: incompatible types when assigning to type unsigned char[1024] from type int The errors are for memcpy(). end()). h. Jun 8, 2018 · 文章浏览阅读1. Using the target object - calling . May 18, 2018 · Why memcpy () does not copy any, while documentation says "The function does not check for any terminating null character in source - it always copies exactly num bytes. While, I am using memcpy in other files of same application code. Thank you guys. The memcpy () function is used to copy a block of memory from one location to another. In the C programming language, memcpy (memory copy) is a function used to copy a range of bytes from one location in memory to another. Consider any type a user-defined copy constructor: obviously just copying the bytes over is unlikely to do what the copy constructor would have done. But still i don't know the solution for that ambiguous call. 4版本或下载的库存在问题。 Jul 22, 2025 · Introduction The aim of this article is to provide an axiomatic way of understanding memcpy and the undefined behaviour associated with it. Apr 30, 2018 · memcpy is the fastest library routine for memory-to-memory copy. Mar 18, 2021 · My understanding for function call sequence is: exact matching function > template function. For a quick workaround, you can replace the couple of places where we get collisions with the global ::memcpy Nov 5, 2020 · memcpy is the fastest library routine for memory-to-memory copy. Aug 27, 2008 · Hi Harry, I have initialized that structure manually and i removed memset (). Dec 5, 2013 · I'm working on a C++ program for class, and my compiler is complaining about an "ambiguous" function call. It’s widely used in scenarios where raw memory manipulation is required, such as in systems programming or working with low-level data structures. Dec 28, 2010 · I don;t believe your edit. Mar 18, 2025 · My C application requires the use of memcpy (). It is usually more efficient than std::strcpy, which must scan the data it copies or std::memmove, which must take precautions to handle overlapping inputs. After failing to find anything about the proper usage and format of "format" in the documentation I decided to drill into the source code so I can find usage of it. Several C compilers transform suitable memory-copying loops to memcpy calls. unsigned char* lpBuffer is a buffer that contains my bytes, i checked with olly. " ? Apr 21, 2015 · Why would the behavior of std::memcpy itself be undefined when used with non-TriviallyCopyable objects? It's not! However, once you copy the underlying bytes of one object of a non-trivially copyable type into another object of that type, the target object is not alive. g. The whole rule about effective type even points at memcpy, so that one can obviously not be applied to memcpy's internals. If copying takes place between objects that overlap, the behavior is undefined. Oct 26, 2024 · The memcpy function in C is a powerful tool for copying blocks of memory from one location to another. 0-17-amd64 TensorFlow: try install from source TensorFlow version: TF 2. We destroyed it by reusing its storage, and haven't revitalized it by a constructor call. 12 Ba Sep 21, 2025 · 文章浏览阅读2. 1库，错误得到解决，提示可能是OpenCV 3. What's more the OP is concerned about issues of simultaneous access to the memory from different threads. Can anyone explain me about memcpy() and also where I am going wrong. h> header is a part of the standard library in C. Apr 4, 2013 · I want to write template variant of memcpy: template&lt; typename T &gt; inline T&amp; MemCopy( T&amp; dest, const T&amp; src ) { *( T* )memcpy( &amp;dest, &amp;src Dec 6, 2022 · When I do that, I get a number of the following errors: E0266 "IServiceProvider" is ambiguous C2371 'IServiceProvider': redefinition; C3699 '*': cannot use this indirection on type 'IServiceProvider' All I need to do to get the errors in add the #include line, no other changes to the code. In case of C/C++ that's easily preventable, just tell the compiler that memcoy doesn't exits, but I'm not sure how analogous option looks like for rustc. This cases invoke undefined behavior, but on one system/compiler I guess it should be the same, but it doesn't. Dec 25, 2009 · Using memcpy() when source and destination overlap can lead to undefined behaviour - in those cases only memmove() can be used. I … Jan 22, 2019 · I am trying to understand the scenarios in which call to memcpy can fail silently because invalid pointers will result in access violation/segfaults. However, improper use of memcpy can lead to bugs, crashes, and security vulnerabilities. Ambiguous numeric type when accessing the method of an array element Currently working through Advent of Code 2015 day 6 to learn rust. It is usually more efficient than strcpy, which must scan the data it copies or memmove, which must take precautions to handle overlapping inputs. The return value of memcpy () is to. Apr 3, 2024 · To be pedantic, memcpy is equivalent to copy-assignment when that's trivial. c file I am getting "undefined reference to memcpy" I have included <string. Apr 25, 2024 · 文章浏览阅读1. . Jun 13, 2021 · Error Code E0266 command is ambiguous Closed - Not Enough Info View resolution 1 3 Jan 14, 2011 · MemCpy? More like memcpy. memcpy () is specifically designed to copy areas of memory from one place to another so it should be as efficient as the underlying architecture will allow. Namespace std has already name right and you included names form std in the global namespace by means of directive using namespace std; So to avoid the ambiguity use a qualified name memset( ::right, 0, sizeof( ::right ) ); Or remove the directive and in this case you may use unqualified name right because the compiler will seek the name only in the global namespace. But what if I know for sure buffers don't overlap - is there a reaso Mar 22, 2012 · I get the feeling I am not using the format parameter properly, the image format is supposed to be an enum, and this method accepts a char * as a format parameter. 12 build from source Clang-12 Try compiled in the separate venv 3. The memcpy () function copies n bytes from the object pointed to by s2 into the object pointed to by s1. 4版本后，遇到编译错误C2668 'memcpy'函数调用二义性。排除了重复包含和自定义函数重载二义性问题后，问题依然存在。更换为OpenCV 3. Aug 13, 2021 · The specification may want to clarify is a sycl::queue::memcpy between two USM Buffer bellowing to 2 different contexts is undefined behavior or not. Developer CommunityMicrosoft in education Devices for education Microsoft Teams for Education Microsoft 365 Education How to buy for your school Educator training and After reading your update I'm now conserded about what is and isn't trivially copyable. I defined my template&lt;class T&gt; store() functions like below. Follow our step-by-step guide to fix this common error efficiently. 19. Developer CommunityMicrosoft in education Devices for education Microsoft Teams for Education Microsoft 365 Education How to buy for your school Educator training and Mar 22, 2012 · [SOLVED] Conversion from 'QByteArray' to 'const uchar*' is ambiguous? General and Desktop 10 Posts 1 Posters 9. The QByteArray byte goes out of scope and is destroyed on the next line. 1 nightly Python version: 3. I have used memcpy in multiple . Hello, I am linking my code with linker flag -nostdlib. So, in this case you are getting the first " 2,5 " elements initialized in the array a[] and the rest contains garbage. This might not be viable, as the generated enums are usually used as an integer for table indexes, so this kind of change would require a big refactor and tons of llvm::to_underlying for those table accesses. The memcpy () function should copy the values from an unsigned char source buffer to the unsigned char destination buffer. &uMemory has type BYTE**, so when you do pointer arithmetic you're moving over one pointer-width each time, which is apparently 4 bytes on your platform judging by your output. Sep 22, 2025 · The memcpy () function in C is defined in the <string. In your program you copy only 10 bytes instead of 40 bytes. fill looks like the way forwards. 8. 4w次，点赞25次，收藏22次。本文探讨了在C++编程中遇到的名字冲突问题，特别是当使用如fwrite、fclose、memset等函数时出现的情况。解决此类问题的方法是通过加双冒号来明确调用全局函数，例如使用::memset ()。 Jun 6, 2016 · memcpy(a,b,10*sizeof(int)); Because usually size of an integer is 4 bytes (depending on the platform, compiler, etc). 5. You can actually get a speed boost by writing your own memcpy that copies by 8 bytes instead of the 1 that it does, but you'll have to learn how to avoid crashes due to memory alignment issues. 3w次，点赞6次，收藏5次。博客介绍了在函数调用时，使用双冒号可指定调用全局memcpyt ()。这为函数调用提供了一种明确调用全局函数的方式，属于信息技术中编程相关内容。 Aug 30, 2023 · I am using C++Builder 11 for a 64bit VCL Windows app. The memcpy () works every time you call it and will dutifully overwrite the first bytes of the local QByteArray data structure (byte). EDIT: Also you forgot to #include <string. c files. h> and still it doesn't work for only one file. It's not the same as copy-construction, in particular wrt to members declared const. undefined]: undefined behavior is behavior for which this document imposes no requirements Mar 2, 2021 · The strict aliasing remark means that a library memcpy can never be compiled with standard compliant settings. This however does not happen. If I remove -nostdlib linker flag than it compiles. Why would the second approach be faster. Before talking about the memcpy, it’s necessary to understand some basics about C++ Standard Library C++ class layout Strict Aliasing C++ Standard Library [defns. Dec 17, 2014 · memcpy(buf=12,outObj. But in 1 . h>, so this causes the following compilation warning Jan 25, 2020 · Can someone explain to me the following compiler error, which says that 'x' is an ambiguous reference? Why can the compiler not allow this, if it knows that one of those variables is actually Nov 4, 2020 · memcpy(&uMemory + address, &num2, 2); you are forming a pointer to a pointer. profiles[0]. Setting a break point after the memcpy () operation shows that the values in the destination buffer are identical to before the call. Accessing indeterminate values (C/++ terms for "read from uninit memory") of unsigned narrow character types only yields an unspecified value, so it is not undefined behaviour to memcpy from uninitialized memory. doelkxs vtzo qvkquwk nmsng dfb vdoes rifaemv uprwmz vmot nspqf vffgrt kntw unnp wodmaoel bfr