C++ std::accumulate 与策略执行未找到

Question

我想使用 C++17 的新并行设施，但我的计算机不这样做。

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这有效：

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finalOutline.push_back(std::accumulate(intermediateCoefs.begin(), intermediateCoefs.end(),origin,[](sf::Vector2f prev, sf::Vector2f current) {\n            return sf::Vector2f(current.x + prev.x, current.y + prev.y);\n        }));\n

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但这不起作用：

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finalOutline.push_back(std::accumulate(std::execution::seq, intermediateCoefs.begin(), intermediateCoefs.end(),origin,[](sf::Vector2f prev, sf::Vector2f current) {\n            return sf::Vector2f(current.x + prev.x, current.y + prev.y);\n        }));\n

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这里是错误消息：

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/home/mbs/Bureau/cplusplusWorkspace/sauvegardeGit/compresse-moi-ces-cercles/src/Model.cpp: In member function \xe2\x80\x98void Model::computeFinalOutline(int)\xe2\x80\x99:\n/home/mbs/Bureau/cplusplusWorkspace/sauvegardeGit/compresse-moi-ces-cercles/src/Model.cpp:246:47: error: no matching function for call to \xe2\x80\x98accumulate(const __pstl::execution::v1::sequenced_policy&, std::vector<sf::Vector2<float> >::iterator, std::vector<sf::Vector2<float> >::iterator, sf::Vector2f&, Model::computeFinalOutline(int)::<lambda(sf::Vector2f, sf::Vector2f)>)\xe2\x80\x99\n  246 |         finalOutline.push_back(std::accumulate(std::execution::seq, intermediateCoefs.begin(), intermediateCoefs.end(),origin,[](sf::Vector2f prev, sf::Vector2f current) {\n      |                                ~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n  247 |             return sf::Vector2f(current.x + prev.x, current.y + prev.y);\n      |             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n  248 |         }));\n      |         ~~                                     \n\n

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我确实包括了需要的内容（我猜）：

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#include <numeric>\n#include <execution>\n

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当我执行程序时，我总是显示 __cplusplus 的版本，其值为：202002

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这是我的 CMAKE 文件（但我认为它没有用）：

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cmake_minimum_required(VERSION 3.22) # way overkill\n\nproject(Taratari)\n\nset (CMAKE_CXX_STANDARD 20) \nset (CMAKE_CXX_STANDARD_REQUIRED ON)\n\nset(CMAKE_CXX_FLAGS_DEBUG_INIT "-g -Wall -Wextra -pedantic -Werror") \nset(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++2a") \n\n\ninclude_directories(\n    $(PROJECT_SOURCE_DIR)/include\n    $(PROJECT_SOURCE_DIR)/src\n)\n\nfile(GLOB all_SRCS\n    "${PROJECT_SOURCE_DIR}/include/*.h"\n    "${PROJECT_SOURCE_DIR}/src/*.cpp"\n)\n    \nadd_compile_options(\n       -mavx\n)\n    \n#sfml\nfind_package(SFML REQUIRED system graphics network audio window) #too much flag no ?\n\n\nadd_executable(exe ${all_SRCS})\n\ntarget_link_libraries(exe PRIVATE sfml-audio sfml-graphics sfml-network sfml-system sfml-window) \n\n

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确实，这是 gcc -v ：

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Using built-in specs.\nCOLLECT_GCC=gcc\nCOLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper\nOFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa\nOFFLOAD_TARGET_DEFAULT=1\nTarget: x86_64-linux-gnu\nConfigured with: ../src/configure -v --with-pkgversion='Ubuntu 11.1.0-1ubuntu1~20.04' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs --enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr --with-gcc-major-version-only --program-suffix=-11 --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib --enable-libphobos-checking=release --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch --disable-werror --disable-cet --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-offload-targets=nvptx-none=/build/gcc-11-2V7zgg/gcc-11-11.1.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-2V7zgg/gcc-11-11.1.0/debian/tmp-gcn/usr --without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu --with-build-config=bootstrap-lto-lean --enable-link-serialization=2\nThread model: posix\nSupported LTO compression algorithms: zlib zstd\ngcc version 11.1.0 (Ubuntu 11.1.0-1ubuntu1~20.04) \n\n

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所以，我不明白发生了什么事。我需要编译标志吗？（但文档没有提及）。

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感谢您的帮助，祝您有美好的一天:-)

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Answer 1

std::accumulate意味着按顺序应用二元运算，因此使用执行策略没有任何意义。它没有任何接受重载的重载（请参阅https://en.cppreference.com/w/cpp/algorithm/accumulate）。

如果您想允许使用某些执行策略进行无序评估，请替换std::accumulate为std::reduce。std::reduce可以假设操作的交换性和结合性，以将其重新排序为任何排列并将其应用于元素的任何分组。