C++ compilation error: A header file is referenced multiple times, how to solve it?

Object slice refers to the phenomenon that only part of the base class data is copied when assigning or passing a derived class object to a base class object, resulting in the loss of new members of the derived class. 1. Object slices occur in containers that directly assign values, pass parameters by value, or store polymorphic objects in storage base classes; 2. The consequences include data loss, abnormal behavior and difficult to debug; 3. Avoiding methods include passing polymorphic objects using pointers or references, or using smart pointers to manage the object life cycle.

RAII is an important technology used in resource management in C. Its core lies in automatically managing resources through the object life cycle. Its core idea is: resources are acquired at construction time and released at destruction, thereby avoiding leakage problems caused by manual release. For example, when there is no RAII, the file operation requires manually calling fclose. If there is an error in the middle or return in advance, you may forget to close the file; and after using RAII, such as the FileHandle class encapsulates the file operation, the destructor will be automatically called after leaving the scope to release the resource. 1.RAII is used in lock management (such as std::lock_guard), 2. Memory management (such as std::unique_ptr), 3. Database and network connection management, etc.

There are many initialization methods in C, which are suitable for different scenarios. 1. Basic variable initialization includes assignment initialization (inta=5;), construction initialization (inta(5);) and list initialization (inta{5};), where list initialization is more stringent and recommended; 2. Class member initialization can be assigned through constructor body or member initialization list (MyClass(intval):x(val){}), which is more efficient and suitable for const and reference members. C 11 also supports direct initialization within the class; 3. Array and container initialization can be used in traditional mode or C 11's std::array and std::vector, support list initialization and improve security; 4. Default initialization

High-frequency trading is one of the most technologically-rich and capital-intensive areas in the virtual currency market. It is a competition about speed, algorithms and cutting-edge technology that ordinary market participants are hard to get involved. Understanding how it works will help us to have a deeper understanding of the complexity and specialization of the current digital asset market. For most people, it is more important to recognize and understand this phenomenon than to try it yourself.

The bit operator in C is used to directly operate binary bits of integers, and is suitable for systems programming, embedded development, algorithm optimization and other fields. 1. Common bit operators include bitwise and (&), bitwise or (|), bitwise XOR (^), bitwise inverse (~), and left shift (). 2. Use scenario stateful flag management, mask operation, performance optimization, and encryption/compression algorithms. 3. Notes include distinguishing bit operations from logical operations, avoiding unsafe right shifts to signed numbers, and not overuse affecting readability. It is also recommended to use macros or constants to improve code clarity, pay attention to operation order, and verify behavior through tests.

The destructor in C is a special member function that is automatically called when an object is out of scope or is explicitly deleted. Its main purpose is to clean up resources that an object may acquire during its life cycle, such as memory, file handles, or network connections. The destructor is automatically called in the following cases: when a local variable leaves scope, when a delete is called on the pointer, and when an external object containing the object is destructed. When defining the destructor, you need to add ~ before the class name, and there are no parameters and return values. If undefined, the compiler generates a default destructor, but does not handle dynamic memory releases. Notes include: Each class can only have one destructor and does not support overloading; it is recommended to set the destructor of the inherited class to virtual; the destructor of the derived class will be executed first and then automatically called.

To determine whether std::optional has a value, you can use the has_value() method or directly judge in the if statement; when returning a result that may be empty, it is recommended to use std::optional to avoid null pointers and exceptions; it should not be abused, and Boolean return values or independent bool variables are more suitable in some scenarios; the initialization methods are diverse, but you need to pay attention to using reset() to clear the value, and pay attention to the life cycle and construction behavior.

There are two main ways to generate random numbers in C. 1. The rand() function in use needs to be used to set the seed with srand(), but the randomness is poor; 2. It is recommended to use the C 11 library to achieve higher quality random number generation through random_device, mt19937 engine and distribution objects. Be careful to avoid repeated seed setting, avoid direct molding control range, and prioritize modern libraries to ensure cross-platform consistency and random quality.