std::string GetString()\n{\n std::string str = \"hello world\";\n return std::move(str); \/\/ bad\n return str; \/\/ ok\n}<\/code><\/pre>\n\n\n\n\u9488\u5bf9\u8fd9\u4e2a\u95ee\u9898\uff0c\u6211\u5728compiler explorer\u4e2d\u505a\u4e86\u6d4b\u8bd5\uff08https:\/\/gcc.godbolt.org\/<\/a>\uff09\uff0c\u5728\u6ca1\u6709\u4f18\u5316\u7684\u7248\u672c\uff0cgcc\u7684\u6c47\u7f16\u7ed3\u679c\u4e2d\u53ef\u4ee5\u770b\u5230\uff0cbad\u7684\u90a3\u79cd\u60c5\u51b5\uff0c\u591a\u505a\u4e86\u4e00\u6b21\u79fb\u52a8\u6784\u9020\uff0c\u800cok\u7684\u90a3\u79cd\u60c5\u51b5\u5219\u6ca1\u6709\u3002<\/p>\n\n\n\n\u8fd9\u6b21\u770b\u6c47\u7f16\u4ee3\u7801\u4e5f\u8ba9\u6211\u66f4\u52a0\u719f\u6089\u4e86\u4e00\u4e22\u4e2264\u4f4dx64\u7684c++\u6c47\u7f16\uff0c\u4e0d\u518d\u662f32\u4f4d\u4e2decx\u4f5c\u4e3athis\u6307\u9488\uff0c64\u4f4d\u4e2d\u51fd\u6570\u7684\u4f20\u53c2\u662f\u5f53\u53c2\u6570\u5c11\u4e8e7\u4e2a\u65f6\uff0c \u53c2\u6570\u4ece\u5de6\u5230\u53f3\u653e\u5165\u5bc4\u5b58\u5668: rdi, rsi, rdx, rcx, r8, r9<\/p>\n\n\n\n
\u53c2\u6570\u4e3a7\u4e2a\u4ee5\u4e0a\u65f6\uff0c \u524d 6 \u4e2a\u4e0e\u524d\u9762\u4e00\u6837\uff0c \u4f46\u540e\u9762\u7684\u4f9d\u6b21\u4ece \u201c\u53f3\u5411\u5de6\u201d \u653e\u5165\u6808\u4e2d\uff0c\u5373\u548c32\u4f4d\u6c47\u7f16\u4e00\u6837\u3002<\/p>\n\n\n\n
\u53c2\u8003http:\/\/abcdxyzk.github.io\/blog\/2012\/11\/23\/assembly-args\/<\/a><\/p>\n\n\n\n\u6211\u8fd8\u5728https:\/\/quick-bench.com\u4e2d\u5bf9\u4e24\u79cd\u4e0d\u540c\u7684\u8fd4\u56de\u65b9\u5f0f\u7684\u901f\u5ea6\u8fdb\u884c\u4e86\u6d4b\u8bd5<\/p>\n\n\n\n
\u6d4b\u8bd5\u4ee3\u7801\u5982\u4e0b<\/p>\n\n\n\n
#include <string>\n#include <iostream>\n\/\/ Type your code here, or load an example.\nstd::string GetString1()\n{\n std::string str = \"hello world\";\n return std::move(str); \/\/ bad\n}\nstd::string GetString2()\n{\n std::string str = \"hello world\";\n return str;\n}\nvoid func1(benchmark::State& state)\n{\n for (auto _ : state) {\n std::string s = GetString1();\n benchmark::DoNotOptimize(s);\n }\n}\nvoid func2(benchmark::State& state)\n{\n for (auto _ : state) {\n std::string s = GetString2();\n benchmark::DoNotOptimize(s);\n }\n}\nBENCHMARK(func1);\nBENCHMARK(func2);<\/code><\/pre>\n\n\n\n\n![\"\"](\"http:\/\/139.224.63.49\/wp-content\/uploads\/2021\/12\/\u6355\u83b74.png\")
<\/figure>\n\n\n\n![\"\"](\"http:\/\/139.224.63.49\/wp-content\/uploads\/2021\/12\/\u6355\u83b73.png\")
<\/figure>\n\n\n\n![\"\"](\"http:\/\/139.224.63.49\/wp-content\/uploads\/2021\/12\/\u6355\u83b72.png\")
<\/figure>\n\n\n\n![\"\"](\"http:\/\/139.224.63.49\/wp-content\/uploads\/2021\/12\/\u6355\u83b7.png\")
<\/figure>\n<\/figure>\n\n\n\n\u53ef\u4ee5\u770b\u5230\uff0c\u5373\u4f7f\u7528\u4e86O3\u6216\u8005OFast\uff0cgcc\u7f16\u8bd1\u7684\u7a0b\u5e8f\u4e2d\uff0c\u8fd8\u662ffunc1\u8fd8\u662f\u4f1a\u663e\u8457\u6162\u4e8efunc2,\u5728clang\u4e2d\u5219\u4f3c\u4e4e\u88ab\u4f18\u5316\u6210\u4e00\u6837\u7684\u4e86\u3002<\/p>\n\n\n\n
no.2<\/p>\n\n\n\n
#include <iostream>\n#include <vector>\n#include <numeric>\nusing namespace std;\nint main()\n{\n vector<float> v{0.2,0.3,0.4};\n double sum = accumulate(begin(v),end(v),0);\n cout<<\"sum = \"<<sum<<endl;\/\/output: sum = 0\n return 0;\n}<\/code><\/pre>\n\n\n\n\u8fd9\u4e2a\u95ee\u9898\u662f\u7531\u4e8eaccumulate\u7684\u7c7b\u578b\u53c2\u6570\u5bfc\u81f4\u7684\uff0c\u89c1https:\/\/en.cppreference.com\/w\/cpp\/algorithm\/accumulate<\/p>\n\n\n\n
Common mistakes<\/h4>\n\n\n\n
If left to type inference, op<\/code> operates on values of the same type as init<\/code> which can result in unwanted casting of the iterator elements. For example, std::accumulate(v.begin(), v.end(), 0) likely does not give the result one wishes for when v<\/code> is std::vector<\/a><double>.<\/p>\n\n\n\n\u6211\u81ea\u5df1\u518d\u8865\u5145\u4e2a\u5751\uff1a<\/p>\n\n\n\n
std::lower_bound<\/h1>\n\n\n\ndefault (1)<\/th> template <class ForwardIterator, class T> ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val);<\/td><\/tr> custom (2)<\/th> template <class ForwardIterator, class T, class Compare> ForwardIterator lower_bound (ForwardIterator first, ForwardIterator last, const T& val, Compare comp);<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n\u5bf9comp\u53c2\u6570\u7684\u8981\u6c42\u4e3a\uff1a<\/p>\n\n\n\n
comp Binary function that accepts two arguments (the first of the type pointed by ForwardIterator<\/samp>, and the second, always val<\/var>), and returns a value convertible to bool<\/code>. The value returned indicates whether the first argument is considered to go before the second.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.<\/p>\n\n\n\nstd::upper_bound<\/h1>\n\n\n\ndefault (1)<\/th> template <class ForwardIterator, class T> ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val);<\/td><\/tr> custom (2)<\/th> template <class ForwardIterator, class T, class Compare> ForwardIterator upper_bound (ForwardIterator first, ForwardIterator last, const T& val, Compare comp);<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n\u5bf9comp\u51fd\u6570\u7684\u8981\u6c42\u4e3a\uff1a<\/p>\n\n\n\n
Binary function that accepts two arguments (the first is always val<\/var>, and the second of the type pointed by ForwardIterator<\/samp>), and returns a value convertible to bool<\/code>. The value returned indicates whether the first argument is considered to go before the second.
The function shall not modify any of its arguments.
This can either be a function pointer or a function object.<\/p>\n\n\n\n\u867d\u7136lower_bound\u548cupper_bound\u51fd\u6570\u7684\u7b7e\u540d\u7279\u522b\u76f8\u4f3c\uff0c\u4f46\u662fcomp\u51fd\u6570\u662f\u4e0d\u540c\u7684\uff01\uff01lower_bound\u8981\u6c42\u7684comp\u662fcmp(*iterator,val)->bool \u800cupper_bound\u8981\u6c42\u7684comp\u662fcmp(val,*iterator)->bool \u6240\u4ee5\u8fd9\u4e24\u4e2acmp\u7684\u4e24\u4e2a\u53c2\u6570\u987a\u5e8f\u662f\u76f8\u53cd\u7684\uff01\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"