C++ 指向地图的指针
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Pointer to a map
提问by Lightness Races in Orbit
If I define a pointer-to-maplike this:
如果我map像这样定义一个指针：
map<int, string>* mappings;
mappingsis a pointer. How should I use this pointer to operate the map?
mappings是一个指针。我应该如何使用这个指针来操作地图？
回答by Lightness Races in Orbit
Use the pointer just like you use any other pointer: dereference it to get to the object to which it points.
使用指针就像使用任何其他指针一样：取消引用它以获取它指向的对象。
typedef std::map<int, string>::iterator it_t;
it_t it1 = mappings->begin(); // (1)
it_t it2 = (*mappings).begin(); // (2)
string str = (*mappings)[0]; // (3)
Remember that a->bis — mostly — equivalent to (*a).b, then have fun!
请记住，这a->b- 主要 - 相当于(*a).b，然后玩得开心！
(Though this equivalence doesn't hold for access-by-index like (*a)[b], for which you may not use the ->syntax.)
（虽然这种等价性不适用于像 那样按索引访问(*a)[b]，您可能不使用->语法。）
回答by iammilind
Not much difference except that you have to use ->for accessing the mapmembers. i.e.
除了您必须->用于访问map成员之外，没有太大区别。IE
mapping->begin() or mapping->end()
If you don't feel comfortable with that then you can assign a referenceto that and use it as in the natural way:
如果您对此感到不舒服，那么您可以为其分配一个引用并以自然的方式使用它：
map<int, string> &myMap = *mappings; // 'myMap' works as an alias
^^^^^^^^
Use myMapas you generally use it. i.e.
用myMap你一般使用它。IE
myMap[2] = "2";
myMap.begin() or myMap.end();
回答by Nicola Musatti
For instance:
例如：
#include <map>
#include <string>
#include <iostream>
int main() {
std::map<int, std::string> * mapping = new std::map<int, std::string>();
(*mapping)[1] = "test";
std::cout << (*mapping)[1] <<std::endl;
}
回答by ofir
another nice way of using pointers, which I like is calling mappings->(and the function you want to call)
另一种使用指针的好方法，我喜欢调用 mappings->（以及你想调用的函数）
回答by Aman Agarwal
Well, STL is designed to reduce the complexity of pointer handling..so better approach is to use stl::iterator.. try to avoid pointers :-/
好吧，STL 旨在降低指针处理的复杂性..所以更好的方法是使用 stl::iterator.. 尽量避免指针：-/
