C ++如何初始化堆中的对象数组

Question

Given a simple class MyClass with a constructor that accepts two int , how can I initialize an array of MyClass in the heap ?

I've tried

MyClass *classes[2] = { new MyClass(1, 2),
                        new MyClass(1, 2) };

But this doesn't seem to work. Thanks

Answer 1

Use the std::allocator<MyClass> for this.

std::allocator<MyClass> alloc;
MyClass* ptr = alloc.allocate(2);  //allocate
for(int i=0; i<2; ++i) {
    alloc.construct(ptr+i, MyClass(1, i)); //construct in C++03
    //alloc.construct(ptr+i, 1, i); //construct in C++11
}

//use

for(int i=0; i<2; ++i) {
    alloc.destroy(ptr+i); //destruct
}
alloc.deallocate(ptr); //deallocate

Note that you don't have to construct all that you allocate.

Or, better yet, just use std::vector .

[EDIT] KerrekSB suggested this as simpler:

MyClass** ptr = new MyClass*[3];
for(int i=0; i<4; ++i)
    ptr[i] = new MyClass(1, i);

//use

for(int i=0; i<4; ++i)
   delete ptr[i];
delete[] ptr;

It's slightly slower access, but much easier to use.