How can I discover the size/length(in bytes) of a

问题:

I have a vector and I want to write and read it to a file but it is not possible to determine the logical size of a vector using the sizeof operator.

So what shall I do?

回答1:

A c++ std::vector has a method size() which returns its size.

EDIT: as I get it now you need to compute the memory a given vector uses. You can't use sizeof for that as a vector uses dynamic memory and stores only a pointer of a dynamic array containing its elements. So my best suggestion would be to multiply the memory each element requires by the number of elements. Note this again will not work if the objects stores a pointer to some dynamically allocated objects - you will have again to compute their sizes separately.

There is no easy way to compute the memory a vector size in bytes in c++ that I know of.