std :: vector默认构造函数是否可以抛出异常

Question

If I construct an empty std::vector using the default constructor (and the default allocator), can it throw an exception?

In general, allocating space for the elements of a container can throw an exception (which would be a std::bad_alloc ). But the default constructor of a std::vector does not need to allocate any such space; it can lazily allocate some space on the first insertion or assignment. But does the C++ standard require that it does not throw exceptions (implying lazy allocation, or catching std::bad_alloc and then falling back to lazy allocation)?

Answer 1

It depends on the default constructor of Allocator . The default constructor of std::vector is declared as

 vector() noexcept(noexcept(Allocator())); (since C++17) 

And if std::allocator is used then it's noexcept(true) ; ie won't throw exceptions.

 allocator() noexcept; (since C++11) 

Hence, before C++17, or if using a non-default allocator, throwing exceptions is possible.