STL unordered_set如何设置初始桶数

Question

对于unordered_map我设置这个初始桶数：

unordered_map<string, dictionaryWord> dictionary(17749); // set initial bucket count to 17749 

似乎这种方式并不为unordered_set工作。

/*line 150*/ unsigned char mask; 
/*line 151*/ unordered_set<QueryID> query_id(109); // set initial bucket count to 109 

编译错误= 1）数字常数之前预期标识符。 2）在数字常量之前预期'，'或'...'。 并继续与一堆的错误

如何做一个unordered_set相同的事情？

谢谢。

============================================== ===

有没有错误，如果我删除“（109）”

"/usr/bin/make" -f nbproject/Makefile-Release.mk QMAKE= SUBPROJECTS= .clean-conf 
make[1]: Entering directory `/home/petros/NetBeansProjects/ACM_test' 
rm -f -r build/Release 
rm -f dist/Release/GNU-Linux-x86/acm_test 
make[1]: Leaving directory `/home/petros/NetBeansProjects/ACM_test' 


CLEAN SUCCESSFUL (total time: 80ms) 

"/usr/bin/make" -f nbproject/Makefile-Release.mk QMAKE= SUBPROJECTS= .build-conf 
make[1]: Entering directory `/home/petros/NetBeansProjects/ACM_test' 
"/usr/bin/make" -f nbproject/Makefile-Release.mk dist/Release/GNU-Linux-x86/acm_test 
make[2]: Entering directory `/home/petros/NetBeansProjects/ACM_test' 
mkdir -p build/Release/GNU-Linux-x86/ref_impl 
rm -f build/Release/GNU-Linux-x86/ref_impl/core.o.d 
g++ -pthread -O3 -std=c++11 -c -O2 -pthread -O3 -std=c++11 -MMD -MP -MF build/Release/GNU-Linux-x86/ref_impl/core.o.d -o build/Release/GNU-Linux-x86/ref_impl/core.o ref_impl/core.cpp 
ref_impl/core.cpp:151:37: error: expected identifier before numeric constant 
ref_impl/core.cpp:151:37: error: expected ‘,’ or ‘...’ before numeric constant 
ref_impl/core.cpp: In function ‘ErrorCode StartQuery(QueryID, const char*, MatchType, unsigned int)’: 
ref_impl/core.cpp:250:24: error: expected unqualified-id before ‘(’ token 
ref_impl/core.cpp:250:38: error: missing template arguments before ‘)’ token 
ref_impl/core.cpp:250:39: error: expected ‘;’ before ‘query_id’ 
ref_impl/core.cpp:257:19: error: ‘query.SameQueries::query_id’ does not have class type 
ref_impl/core.cpp: In function ‘ErrorCode EndQuery(QueryID)’: 
ref_impl/core.cpp:265:44: error: ‘queries.std::vector<_Tp, _Alloc>::operator[]<SameQueries, std::allocator<SameQueries> >(((std::vector<SameQueries>::size_type)i)).SameQueries::query_id’ does not have class type 
ref_impl/core.cpp:265:58: error: unable to deduce ‘const auto’ from ‘<expression error>’ 
ref_impl/core.cpp:266:38: error: ‘queries.std::vector<_Tp, _Alloc>::operator[]<SameQueries, std::allocator<SameQueries> >(((std::vector<SameQueries>::size_type)i)).SameQueries::query_id’ does not have class type 
ref_impl/core.cpp:267:32: error: ‘queries.std::vector<_Tp, _Alloc>::operator[]<SameQueries, std::allocator<SameQueries> >(((std::vector<SameQueries>::size_type)i)).SameQueries::query_id’ does not have class type 
ref_impl/core.cpp:268:36: error: ‘queries.std::vector<_Tp, _Alloc>::operator[]<SameQueries, std::allocator<SameQueries> >(((std::vector<SameQueries>::size_type)i)).SameQueries::query_id’ does not have class type 
ref_impl/core.cpp: In function ‘void* TaskCode(void*)’: 
ref_impl/core.cpp:463:41: error: ‘quer.SameQueries::query_id’ does not have class type 
ref_impl/core.cpp:463:48: error: unable to deduce ‘auto’ from ‘<expression error>’ 
ref_impl/core.cpp:463:70: error: ‘quer.SameQueries::query_id’ does not have class type 
make[2]: *** [build/Release/GNU-Linux-x86/ref_impl/core.o] Error 1 
make[2]: Leaving directory `/home/petros/NetBeansProjects/ACM_test' 
make[1]: *** [.build-conf] Error 2 
make[1]: Leaving directory `/home/petros/NetBeansProjects/ACM_test' 
make: *** [.build-impl] Error 2 


BUILD FAILED (exit value 2, total time: 1s) 

Answer 1

这是一个结构里面。它应该是：

unordered_set<QueryID> query_id = unordered_set<QueryID>(109); 

谢谢

Answer 2

我怀疑斗数是一个红色的鲱鱼。它看起来像QueryID是不可见的。

Answer 3

我怀疑你的QueryID没有标准的构造函数，即QueryID::QueryID() { std::cout << "foo!" };所以无序集不知道如何预先填充空的QueryID。

尝试添加一个。

或者您可以使用第二个参数设置每个预建存储桶使用的默认数据。

参考： http://en.cppreference.com/w/cpp/container/unordered_set/unordered_set