c++ convert pointer to vector

The other answers show how to make a copy of the returned array and create a vector, but assuming the API allocates memory for the array and expects the caller to delete it, you may also want to consider sticking the array into a smart pointer and using it as is. Is Pelosi's trip to Taiwan an "official" or "unofficial" visit? I will not answer directly your question, but maybe provide some useful information. ref: https://en.cppreference.com/w/cpp/utility/functional/reference_wrapper, std::vector value_vec (value, value + n); //suppose value has n elements. vector::iterator to T*? Why is reading lines from stdin much slower in C++ than Python? To learn more, see our tips on writing great answers. Be the first to rate this post. Even if I know the size of the array, I'm not always iterating through it entirely so the loop count has to be a variable, but the vectorizer works fine even with a loop limit not constant when compiling C code from Clang for example so I should be able to do the same for this code .. (hopefully :) ), to James Courtier-Dutton, llv@cs.uiuc.edu, http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev. If vector::iterator is a class type, then this code is valid C++; What is the equivalent of the Run dialogue box in Windows for adding a printer? No iterator wrapper can allow this kind of pointer conversion, because it Do you need video marketing services? but theres no reason it should be implicitly convertible to vector::iterator. We take care of your website SEO optimization factors. itll also consider std::iter_swap as a candidate, but As hidden friend will be Unfortunately, the Clipper.jl library currently only supports Vector. The caveat is that you have got to zero out the pointers after use in order to avoid double-freeing the memory. This post will discuss how to convert an array to a vector in C++. You can still copy this into a vector but if you do the above steps you don't have to worry about deleting the returned array. Can my aliens develop their medical science, in spite of their strict ethics? Citations are very important for local marketing. I am getting the error C2440: 'reinterpret_cast' : cannot convert from 'std::vector<_Ty>' to 'std::vector<_Ty>' why? think that they should just define these iterators as aliases for T* I will probably keep ordering local marketing services for years to come! If both vector::iterator and string::iterator were aliases for char*, We can also use the std::copy STL algorithm, which copies the specified range of elements to another range beginning from the specified output iterator. so you must not wrap stack allocated array pointer like this. See Although the mutations of the elements of an array of immutable structs change the pointers, that happens in the stack, thus this is very fast and does not allocate. The idea is to use the vectors range constructor that constructs a vector from elements of the specified range defined by two input iterators. We can also use the std::assign function that replaces the existing contents of the vector with elements of the specified range. See ADL can interfere even with uglified names (2019-09-26) The result is a Base.ReinterpretArray{IntPoint, 1}, which is a subtype of AbstractVector{IntPoint}. Is it because STL assumes that the reserved size is a power of 2? but explicit. mangled names). Why is processing a sorted array faster than processing an unsorted array? it is initialized with the result of v.end().operator--(). What is the nature of a demiplane's walls? If vector::iterator is std::__wrap_iter, We can avoid that in C++11, which introduced std::begin and std::end functions that return an iterator pointing to the beginning and the end of a sequence. Local markting is very important for any kind of local business. Type casting can lead to strange errors when done wrong, so it is better to avoid this or handle it with greatest care. for details on the Holder pattern. Can you run the SLP-vectorizer with the flag -mllvm -debug-only=SLP and attach the log ? but __wrap_iter and __wrap_iter are not similar. No votes so far! If you are a local business owner you should already know that its getting even more complicated to have more clients knocking on your door. email is in use. A naive solution is to use the simple for-loop that iterates the array and add all its values to the vector one at a time using the push_back() function. Any kind of vector operations that you may want to hard-code will make it not work on anything other than the intrinsics/inline asm you're using, which is not a good idea. Besides the obvious ABI breakage, If your code didn't get vectorized, it's possible that it is not clear enough that that pointer is being iterated in a way that it's easy for the vectorizer to spot, so maybe you need to make it clearer, and that depends on the code in question. If vector::iterator were an alias for int*, then the call to f above By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How can I refill the toilet after the water has evaporated from disuse? One thing I find helpful in these situations is to use type definitions. the better match. contiguous iterator types vector::iterator and so on. This is possible because the elements in a vector are stored contiguously. Is any finite-dimensional algebra a sub-algebra of a finite-group algebra? Our mission is to bring you more customers. Enter your email address to subscribe to new posts. for details. libc++s iterator wrapper makes that conversion private; libstdc++ makes it public You might As hidden-friend iter_swap. What is "Rosencrantz and Guildenstern" in _The Marvelous Mrs. Maisel_ season 3 episode 5? Making statements based on opinion; back them up with references or personal experience. All Rights Reserved. You shouldn't need to do anything, the vectorizer should spot that for you, if the machine you're compiling to has support for vector instructions. What are the basic rules and idioms for operator overloading? More like San Francis-go (Ep. Nothing prevents a green-field STL implementation from using T* for all these types Our local marketing services will help you business get more customers. There are several ways to use a std::vector as a C array (for example, for compatibility with C libraries). How hana::type disables ADL (2019-04-09), Math Proofs - why are they important and how are they useful? Calculating length of curve based on data points? We have a special offer for you! External hard drive not working after unplugging while Windows Explorer wasn't responding. Love to see results. would become ambiguous. You can't wrap an array in a vector in place and expect the vector to operate on that array. it would alter the ADL behavior of the following snippet: If vector::iterator is A*, this calls the only candidate: debug performance, and even object-file size (because of all those super-long because the vector insists on controlling the allocation and reallocation of its memory. What rating point advantage does playing White equate to? However I am unable to find a way to do this with a Vector{T} instead; my obvious attempt (inserting Vector{} everywhere in the above example) failed with "pointerref: invalid pointer type" (which, I imagine, is due to the difference between a C array and a Julia vector), while calling vec2 = reinterpret(IntPoint, vec1) does return a Vector{IntPoint}, but seems to make a copy (I checked that pointer_from_objref(Ref(vec2[1])) is different from pointer_from_objref(Ref(vec1[1]))). All these wrappers impose a pretty high cost in terms of compilation speed, by defining it as __wrap_iter::type. Simple question with maybe a complex answer: WHY is there no way to wrap an STL vector around an existing plain array (in place) ? and my recent LWG paper P2538 ADL-proof std::projected 20 Bay Street, 11th Floor Toronto, Ontario, Canada M5J 2N8 the completion of Holder. Announcing Design Accessibility Updates on SO, using reinterpret_cast to convert char* to vector. can change the data memory location of the vector, thus invalidating previous data pointers. Thus, if you vector is of elements of one or other type, the elements can be mutated without allocating: So I am trying to convert data of type Vector{T} to Vector{IntPoint} , for passing to the Clipper.jl functions. In fact, it compiles on libc++ today, because libc++ instead. Thanks to @Ethereal for the nice solution and to make his/her answer more complete: that code will not compile in visual c++ (maybe will in GCC) because of differences in the std implementation but with some changes, it will work perfectly. We provide a wide range of local marketing services. Provide an answer or move on to the next question. So I am trying to convert data of type Vector{T} to Vector{IntPoint}, for passing to the Clipper.jl functions (which is a set of wrappers to a C library), without copying the objects (The fact that the IntPoint data are used in ccall, and that SVector holds its data in a tuple, guarantees that casting pointers around is safe). Others have suggested that you cannot wrap an array in a vector, but that's simply not true; think about it, a vector has an array as it's underlying data container! Site design / logo 2022 Stack Exchange Inc; user contributions licensed under CC BY-SA. What would happen if qualified immunity is ended across the United States? But of course that would be both an ABI and API break. 469). then this would compile. You do not have permission to delete messages in this group, Either email addresses are anonymous for this group or you need the view member email addresses permission to view the original message. This modified text is an extract of the original, C++ Debugging and Debug-prevention Tools & Techniques, C++ function "call by value" vs. "call by reference", Curiously Recurring Template Pattern (CRTP), RAII: Resource Acquisition Is Initialization, SFINAE (Substitution Failure Is Not An Error), Side by Side Comparisons of classic C++ examples solved via C++ vs C++11 vs C++14 vs C++17, std::function: To wrap any element that is callable, Find max and min Element and Respective Index in a Vector, Using a Sorted Vector for Fast Element Lookup. Asking for help, clarification, or responding to other answers. ADL can interfere even with uglified names. If a question is poorly phrased then either ask for clarification, ignore it, or. libstdc++s iterator wrapper disallows such conversions. reinterpret_cast conversion - cppreference.com, A question about pointer typecasting in C. How can I solve the suspicious pointer conversion in C? Don't tell someone to read the manual. This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL). Dont miss our future offers! If you could share the code (or a similar example) with the list, people could help you spot the pattern and make it vectorize. 2020, Local Marketing Agency. But, if vector::iterator is std::__wrap_iter::type, Base* and const Base* are similar types, Do you need your, CodeProject, Why are elementwise additions much faster in separate loops than in a combined loop? Awesome services! Understand that English isn't everyone's first language so be lenient of bad (as far as I know), but youll never see any existing library vendor switch to T* Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. But if its int*, then --v.end() is ill-formed: the built-in -- SVector{2,Fixed{64,F}} where{F} (lets call this type T); namely, T will support linear algebra, conversion to/from floats, et.c. Powered by Discourse, best viewed with JavaScript enabled, Reinterpret Tuple as Struct, and vector thereof. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. If the vector has enough space, we can simply specify the output iterator to the beginning of the destination range. I love to see my restaurant getting more clients each month. Get Subscribed now! Is there anything a dual bevel mitre saw can do that a table saw can not? By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. What if vector::iterator were just T*? What would be the best way to perform such an in-place reinterpretation? then std::iter_swap will be the only candidate! Is the US allowed to execute a airstrike on Afghan soil after withdrawal? Image Processing: Algorithm Improvement for 'Coca-Cola Can' Recognition. One way around this would be to do: to get a v of type Vector{IntPoint}. Be sure to wrap GC. An API I'm using provides a result as double* pointer. How do I politely refuse/cut-off a person who needs me only when they want something? involves only primitive types. You need to outrank your competition online. Trending sort is based off of the default sorting method by highest score but it boosts votes that have happened recently, helping to surface more up-to-date answers. (and thus more expensive) than libc++s. Our company provides quality local marketing services. wont trigger the completion of Holder; but comparing two Connect and share knowledge within a single location that is structured and easy to search. spelling and grammar. Both the SLP vectorizer and the Loop vectorizer support vectorizing pointers. Does this JavaScript example create race conditions? Every major C++ standard library vendor defines wrappers for their At 3% inflation rate is $100 today worth $40 20 years ago. Another efficient solution is to use the std::insert function. Trying to relate microphone sensitivity and SPL. can anybody point to where this particular vector constructor is defined in the documentation? So I am playing a bit with the Clipper.jl library, which uses a type IntPoint defined as a struct of two Int64 fields. +1 (416) 849-8900, // this should be written with an iterator loop. For example: Get monthly updates about new articles, cheatsheets, and tricks. suffice it to say that equality-comparing two pointers of type Holder** We are here to help you. I had been attempting this off and on for quite some time before I came up with a workable solution. I think that we are missing the pattern for the roots of the tree.. Heres a list of code snippets that would Get more customers today! and no messing around with unsafe pointer operations. Thats all about converting an array to a vector in C++. Before C++11, you would take the address of the vector's first element to get an equivalent pointer, if the vector isn't empty, these both methods are interchangeable: Note: If the vector is empty, v[0] and v.front() are undefined and cannot be used. I have written star pyramid pattern code using pointer to pointer in C but can't resolve the error, please help, Arrays and pointers with the C programming language. Do NOT follow this link or you will be banned from the site. For a single T object I can do this in the following way: (yes I used to program in C, but a pointer cast seems appropriate here since we are passing this to ccall anyway). The guarantees made by member functions couldn't hold if the vector couldn't control the underlying array. It performs a binary copy of the data and hence is error-prone. Not spammy backlinks. However, it would be more convenient for me to use static vectors of fixed-point reals, i.e. Find centralized, trusted content and collaborate around the technologies you use most. We'll contact you to get specific details and understand what are your target customers. Call us. I highly recommend for all local business owners! How can I tell LLVM to consider this i32* as an <10 x i32> (and thus get the performance improvements thanks to SIMD ..etc..) ? how to convert from vector to vector in c++? I see a bunch of constructors but I don't understand which one this is. In contrast to solutions based on previous C++ standards (see below), the member function .data() may also be applied to empty vectors, because it doesn't cause undefined behavior in this case. The content must be between 30 and 50000 characters. because std::vector is trying to delete the pointer in its destructor, and if array pointer is allocated on the stack it will cause double delete same memory address and it will cause run time error. This could be altered by ADL-proofing vector::iterator, that is, change their behavior if vector::iterator became an alias for T*. (To the extent that they can exist in JavaScript). What is a smart pointer and when should I use one? (Godbolt.). When storing the base address of the vector's data, note that many operations (such as push_back, resize, etc.) Why should I use a pointer rather than the object itself? Quality link building! Derived* is implicitly convertible to Base*; but theres no I want to wrap this with the std::vector type. it would actually be an API break as well! makes both iterator types an alias for __wrap_iter; but it wont compile The null pointer constant nullptr of course can be implicitly converted to T*; I am able to typecast reference of vector to reference of vector whereas I am unable to typecast vector to vector. Today, in practice, every library vendor considers it unambiguous. Since we need to insert new elements at the end of the destination vector, we can use std::back_inserter to the initial position in the destination. The citation services I choose are doing wonders! something return a double* something take a pointer as an argument. // create an empty vector and push all elements. The best you can do is give the vector the double* and the number of values, which will have the vector make a copy of every element and put it in itself: And also, like Praetorian said, if the API you are using expects you to free the memory after using it, you might be interested in smart pointers. Announcing the Stacks Editor Beta release! The attached code looks like a candidate for the SLP-vectorizer. on libstdc++ or MSVC because their aliases are less SCARY this code tested in Microsoft Visual C++ (VS2015): but you should be noticed you can wrap an array pointer in std::vector just if that pointer is allocated in heap(for example using new keyword) Thanks for contributing an answer to Stack Overflow! If what you are saying is that you know the array of i32 will always be 10 entries, make the function use a constant limit=10 to the loop. https://en.cppreference.com/w/cpp/utility/functional/reference_wrapper, San Francisco? Could a library vendor decide to simply change their definition of We are sorry that this post was not useful for you! rev2022.8.2.42721. This is the simplest and very efficient solution. Since the vector is nothing but a dynamic array, the memcpy() function can also work here. Chances are they have and don't get it. Kerrek SB// good point! Alternatively you could just make a class that inherits from vector and nulls out the pointers upon destruction: This will copy the data in values to a std::vector. 468), Monitoring data quality with Bigeye(Ep. reason to permit conversion of iterator-to-Derived to iterator-to-Base. See Praetorian's answer. What is the music theory related to a bass progression of descending augmented 4th from ^7 to ^4? @protect b begin end around any code that needs to use v, to ensure that the underlying array doesnt get garbage-collected while you are using it. If using C++11, you could use a std::vector>. objects of the class type __wrap_iter**> will trigger operator requires a modifiable lvalue, and v.end() would be a prvalue! With the current situation its getting harder to outrank your competition. Otherwise I don't see a reason at the moment why this should not be possible @JakobS. by default: it would break too much existing code. std::vector has an overloaded version of std::insert, which takes three parameters the first parameter is an iterator to the destination vector, and the last two parameters are the iterators specifying a range of array elements.

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