std::cout << " whether A instance has value " << a.has_value(0) << std::endl; std::cout << " whether A instance has const value " << a.has_const_value(0) << std::endl;
功能:Arena allocation is a C++-only feature that helps you optimize
your memory usage and improve performance when working with protocol
buffers.
原因:By default, protocol buffers performs heap allocations for
each message object, each of its subobjects, and several field types,
such as strings. These allocations occur in bulk when parsing a message
and when building new messages in memory, and associated deallocations
happen when messages and their subobject trees are freed.
Message
的构造和释放在堆栈上进行,涉及到动态内存的生成和释放,这一步骤非常昂贵。
查看 version
protoc --version
Python
Enum
Could
not serialize object: TypeError: can't pickle
google.protobuf.pyext._message.EnumDescriptor objects
Exchanges the content of the container by the content of x, which
is another vector object of the same type. Sizes may differ.
After the call to this member function, the elements in this
container are those which were in x before the call, and the elements of
x are those which were in this. All iterators, references and pointers
remain valid for the swapped objects.
Checks if the contents of lhs and rhs are equal, that is, they have
the same number of elements and each element in lhs compares equal with
the element in rhs at the same position.
intmain(){ // Initialize a set. // Compare parameter is default to std::less<Key>. std::set<int> min_s; min_s.insert(1); min_s.insert(3); min_s.insert(2); min_s.insert(5); min_s.insert(4); min_s.insert(-1);
std::cout << "min value of set container is " << *min_s.begin() << std::endl; std::cout << "max value of set container is " << *min_s.rbegin() << std::endl;
// Compare parameter is default to std::greater<Key>. std::set<int, std::greater<int>> max_s; max_s.insert(1); max_s.insert(3); max_s.insert(2); max_s.insert(5); max_s.insert(4); max_s.insert(-1);
std::cout << "max value of set container is " << *max_s.begin() << std::endl; std::cout << "min value of set container is " << *max_s.rbegin() << std::endl;
std::cout << "max value of multiset container is " << *max_ms.begin() << std::endl; std::cout << "min value of multiset container is " << *max_ms.rbegin() << std::endl;
return0; }
输出结果如下
1 2 3 4 5 6
min value of set container is -1 max value of set container is 5 max value of set container is 5 min value of set container is -1 max value of multiset container is 5 min value of multiset container is -1