C++ 错误：“unordered_map”未命名类型
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C++ error: 'unordered_map' does not name a type
提问by user788171
I am doing everything correctly as far as I can tell and I have gotten the error message:
据我所知，我做的一切都是正确的，我收到了错误消息：
error: 'unordered_map' does not name a type
error: 'mymap' does not name a type
In my code, I have:
在我的代码中，我有：
#include <unordered_map>
using namespace std;
//global variable
unordered_map<string,int> mymap;
mymap.reserve(7000);
void main {
return;
}
I don't see what can be missing here....
我看不出这里会缺少什么......
EDIT: when I update my declaration to
编辑：当我将声明更新为
std::tr1::unordered_map<string,int> mymap;
I an able to eliminate the first error, but when I try to reserve, I still get the second error message.
我能够消除第一个错误，但是当我尝试预订时，我仍然收到第二个错误消息。
EDIT2: As pointed out below, reserve must go into main and I need to compile with flag
EDIT2：正如下面所指出的，reserve 必须进入 main，我需要用 flag 编译
-std=c++0x
However, there still appear to be errors related to unordered_map, namely:
但是，似乎仍然存在与 unordered_map 相关的错误，即：
error: 'class std::tr1::unordered_map<std::basic_string<char>, int>' has no member named 'reserve'
回答by gongzhitaao
Compile with g++ -std=c++11(my gcc version is gcc 4.7.2) AND
编译g++ -std=c++11（我的 gcc 版本是gcc 4.7.2） AND
#include <unordered_map>
#include <string>
using namespace std;
//global variable
unordered_map<string,int> mymap;
int main() {
mymap.reserve(7000); // <-- try putting it here
return 0;
}
回答by BarelyEthical
If you want to support
<unordered_map>for versions older than c++11 use#include<tr1/unordered_map>and declare your maps in the form :-std::tr1::unordered_map<type1, type2> mymap
which will use the technical report 1 extension for backward compatibility.
如果您想支持
<unordered_map>早于 c++11 的版本，请使用#include<tr1/unordered_map>并以以下形式声明您的地图：-std::tr1::unordered_map<type1, type2> mymap
这将使用技术报告 1 扩展名以实现向后兼容性。
回答by taocp
You can't execute arbitrary expressions at global scope, so you should put
你不能execute arbitrary expressions at global scope，所以你应该把
mymap.reserve(7000);
inside main.
里面主要。
This is also true for other STL containers like map and vector.
这也适用于其他 STL 容器，如 map 和 vector。
