In C++, structs and unions are two very similar composite data types that can be used to store multiple data types, but there is a big difference between the two.
1. The role of the structure
In network protocol, communication control, C/C++ programming of embedded systems, we often want to transfer not a simple byte stream, but a whole of a combination of multiple data, the form of which is a structure.
2, the definition of the structure
Structure: refers to the definition of the corresponding data structure and the corresponding variables.
The structure is as follows,
Among them, struct is a structure key and must not be omitted.
Node is a structure name, which can be omitted and becomes an unnamed structure.
Structure members can make basic types or construction types.
3, features
Variables are accessed with "." and pointers are accessed with "->". Eg. node.num = 1; node->ame = "abc";
Union1. The role of the union
With overlay techniques, several variables overlap each other, allowing several different variables to occupy a segment of memory structure. All members of the union are stored in a piece of memory, the starting address is the same, and only one of the member variables can be used at a time.
2, the definition of the union
The union is as follows,
The union is a union key and cannot be omitted. Node is the name of the union.
3, features
The body memory length is the length of the longest internal data type.
The address of the union and the address of each member variable are the same address.
Main difference
1. Each member of the structure is used to represent the attributes of a specific transaction. The members of the union can represent multiple attributes (the same storage space can store different types of data).
2. The total space of the structure is equal to the total length of each member. The shared space is equal to the space occupied by the largest member.
3. The union cannot be assigned an initial value and the structure can be.
An electronic clock device with a wireless network monitoring camera is characterized in that it comprises an electronic clock device body with a wireless network monitoring camera; the electronic clock device body with a wireless network monitoring camera is composed of a foot, a wireless transmission module, a It consists of a rechargeable battery, a speaker, a touch display screen, a camera, a casing, an infrared device, and a microprocessor; the feet are fixedly installed at the bottom of the rechargeable battery; a casing is fixedly installed on the top of the rechargeable battery, and the The interior is provided with a touch screen, a camera, an infrared device and a microprocessor; the microprocessor is electrically connected to the rechargeable battery through wires; the wireless transmission module, speaker, display, camera and infrared device are connected to the micro processor through wires The display screen is arranged at the bottom of the camera, and the camera is surrounded by an infrared device; the wireless transmission module is fixedly installed on both sides of the rechargeable battery, and the speakers are opened on both sides of the casing
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