此散列仅适用于枚举类型 [英] This hash only works for enumeration types
问题描述
我正在使用C ++中的一个非常简单的类,它有一个 unordered_map
成员:
I'm working on a (very) simple class in C++ that has a unordered_map
member:
class SDLFontManager : public CPObject, public FontManagerProtocol {
public:
SDLFontManager() {};
// flush the cache when the manager is destroyed
virtual ~SDLFontManager() { flushFontCache(); };
// load a font from the cache if it exists, or load it from file and cache it.
virtual FontProtocol* fontWithTTF(const char* filename) {
if(_cache.find(filename) != _cache.end()) {
return _cache[filename];
}
SDLFont* font = new SDLFont(filename);
_cache[filename] = font;
font->retain();
return font;
}
// flush the font cache
virtual void
flushFontCache() {
for(auto font: _cache) {
font.second->release();
}
}
private:
std::unordered_map<std::string, SDLFont*> _cache;
};
当我编译时,我的类的源代码没有错误,但clang失败,指向我C ++标准库的功能
文件,其中包含以下消息:
When I compile, I get no errors in the class's source, but clang fails, pointing me to the C++ standard library's functional
file, with the following message:
功能:2441:5 :Static_assert failedThis hash only work for enumeration types
我假设 unordered_map
需要的散列函数有一个问题(如果我是正确的,它被实现为HashMap)。当我用一个简单的 map
替换它,一切都编译正确。我有其他 unordered_map
在我的代码库与 std :: string
作为键完全编译。
I assume that there is a problem with the hashing function needed for unordered_map
(which, if I am correct, is implemented as a HashMap). When I replace it with a simple map
, everything compiles properly. I have other unordered_map
s in my codebase with std::string
as keys that compile perfectly.
我有没有发现一些明显的错误?我非常怀疑这将是一个标准的库错误。
Is there some obvious mistake I've not spotted? I'm highly doubt this would be a standard library bug.
(如果可以有任何帮助,代码编译为 clang- 700.0.65
( Apple LLVM版本7.0.0
,随Xcode 7提供),没有异常/ RTTI和 std = c ++ 14
)
(if it can be of any help, the code is compiled with clang-700.0.65
(Apple LLVM version 7.0.0
, shipped with Xcode 7), no exceptions/RTTI, and std=c++14
)
编辑
正如@ dau_sama的回答所指出的,< string>
不是直接包含的(只包括另一个头),这是导致问题的原因。可能的重复是相对不同的,因为 std :: string
不是一个自定义类,标准库为它提供了哈希函数。
As pointed out by @dau_sama's answer, <string>
wasn't included directly (only by including another header), which was causing the problem. The possible duplicate is relatively different, as std::string
is not a custom class and the standard library provides a hash function for it.
推荐答案
您可能缺少字符串头
#include <string>
应该可以解决您的问题
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