使用const char *作为map/unordered_map的键 [英] Using const char* as key for map/unordered_map

问题描述

如何创建将直接使用const char*作为键的地图/无序地图?

How to create map/unordered_map that will use const char* as key directly?

如果我使用map<std::string,..>，则在每次解析map["abc"] = ...时都会创建一个新的std::string对象.这会导致分配内存，创建字符串对象并将字符串复制到其中的大量开销.

If I use map<std::string,..>, then on each resolving map["abc"] = ... a new std::string object will be created. That causes a big overhead for allocating memory, creating a string object and copying the string into it.

如何声明一个直接使用const char*且没有任何开销的地图对象?

How do I declare a map object that uses const char* directly without any overhead?

推荐答案

您可以使用 std::string_view :

You can use a std::string_view:

std::map<std::string_view, int> Map;
Map["abc"] = 1; // no allocation necessary to store "abc"

基本上，它是字符串对象的包装.这是一个视图，这意味着它不拥有字符串，因此不会复制和分配用于存储字符串的内存.

It is basically a wrapper around string objects. And it's a view, which means that it doesn't own the string and thus doesn't copy and allocate memory to store a string.

请注意，对于小字符串(还有文字)，由于 SSO 和因此开销很小.始终在进行优化之前先进行测量.

Note that for small strings (and also literals), std::string doesn't allocate too due to SSO and so the overhead is minimal. Always measure before optimizing.

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