无序集的编译问题
我正在尝试使用 C++ std 库中的 unordered_set 。我正在使用 std 命名空间。
using namespace std;
unordered_set 在我的函数内。我想用它来记住一些值。
int do_crazy_calculations(int n) {
static unordered_set<int> done_before;
done_before::iterator node_found = done_before.find(n);
// n has not been seen before, so do calculations and memoize the result.
if (node_found == done_before.end()) {
int result = actually_do_calculations(n);
done_before.insert(n, result);
return result;
}
// n has already been seen before, just return the memoized value.
else {
return node_found.get();
}
}
但是，我收到此编译错误：
CplusplusExperiment.cpp：在函数
'int do_crazy_calculations(int)'中：
CplusplusExperiment.cpp:10:10: 错误：'unordered_set'未命名类型
make: *** [CplusplusExperiment.o] 错误 1
但是，我确实为 unordered_set - int 分配了一个类型，对吗？这个错误是什么意思？
I am trying to use an unordered_set from the C++ std library. I am using the std namespace.
using namespace std;
The unordered_set is within a function of mine. I would like to use it to memoize some values.
int do_crazy_calculations(int n) {
static unordered_set<int> done_before;
done_before::iterator node_found = done_before.find(n);
// n has not been seen before, so do calculations and memoize the result.
if (node_found == done_before.end()) {
int result = actually_do_calculations(n);
done_before.insert(n, result);
return result;
}
// n has already been seen before, just return the memoized value.
else {
return node_found.get();
}
}
However, I am getting this compilation error:
CplusplusExperiment.cpp: In function
'int do_crazy_calculations(int)':
CplusplusExperiment.cpp:10:10: error:'unordered_set'does not name a type
make: *** [CplusplusExperiment.o] Error 1
However, I did assign a type to unordered_set - int right? What does this error mean?
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using namespace std——这会导致上千个令人沮丧的错误。done_before实际上并不命名类型，而是命名变量。要命名类型，您可以使用 typedef unordered_setdone_before_type::iterator就会起作用。using namespace std-- it's a source of a thousand frustrating errors.done_beforereally doesn't name a type, it names a variable. To name a type you could usetypedef unordered_set<int> done_before_type, thendone_before_type::iteratorwill work.<unordered_set>应该是
unordered_set::iterator node_found = ... 我通常使用 typedef 来简化模板化变量的命名：
should be
unordered_set<int>::iterator node_found = ...I usually use a typedef to simplify naming of templated variables:
首先，unordered_set是TR1或C++11中的。
其次，您在函数内声明该集合，然后测试其中的某些值。有什么意义？每次调用该函数时，集合都会为空。编辑：抱歉，没有注意到它是静态的。
First of all, unordered_set is in TR1 or C++11.
And second, you are declaring the set inside your function and then testing for some value in it. What's the point? The set's gonna be empty each time you call the function. EDIT: sorry, didn't notice it was static.