我可以在不先找到 std map 的情况下更改它的值吗

Question

This is how currently i am changing the value of std::map

std::map<std::string, int> stdmapMasks;
stdmapMasks.insert(std::make_pair("VALUE", 1));
std::map<std::string, int>::iterator it = stdmapMasks.find('VALUE'); 
if (it != stdmapMasks.end())
    it->second = 42;

Can i change the value directly without the need to find the map element ?

Answer 1

C++ has many ways to interact with a map's values without explicitly calling map::find . operator[] allows you to access a value, default constructing it if it does not exist. insert_or_assign from C++17 provides a way to do what operator[] does, save for the requirement of having a default constructor. C++17's try_emplace will emplace-construct the value if the key is not present, but does nothing if there is already a value there.

But no version of C++ has a method like "try_assign", where assignment doesn't happen if the key already exists. So you will have to explicitly find it first.