Application of pointer in STC89C52 single chip microcomputer and demonstration of practical cases

Catalog

Small end allocation mode

C In language * The function of

Data width

Pass parameters

Pass the return value

Directly access the data under the physical address

Access the data in the memory specified by the hardware , Such as equipment ID Number, etc.

Convert complex format data into bytes , Convenient communication and storage

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The pointer (Pointer) yes C An important knowledge point of language , Its use is flexible 、 Powerful , yes C The soul of language

Pointers are closely related to the underlying hardware , Use a pointer to manipulate the address of the data , Realize indirect access to data

Small end allocation mode ：

Store the number from small to large in the address from small to large , This storage method is called small end allocation

Different variables in the array are also stored in the order of address from small to large , No other data is stored in the middle .

The same if short c[ ] This type , Then each data is internally divided into short The way to store , Instant 2 Byte store , Different data are stored in sequence

C In language * The function of ：

1, Multiplication sign

2, Define pointer

3, Take out the data

Data width ：

The pointer takes a data as the basic unit when adding and subtracting , Otherwise, it's meaningless .

If the definition is int Pointer to type , Then adding and subtracting is equivalent to adding and subtracting 4 Bytes .

C Use language skillfully & And * Transform the data , Ensure that the pointer level is consistent , If necessary, you may need to use a cast ：

float num;

unsigned char *p;

p=(unsigned char *)#

The following is about C Common pointer uses in languages ：

Pass parameters

Use a pointer to pass a large number of parameters （ Array ）, The main function and the sub function use the same set of data , Avoid data duplication during parameter transfer , Improved operational efficiency , Reduced memory usage

Use pointers to pass output parameters , Using the same set of data for main function and sub function , Realize the return of data , Can realize the design of multi return value function

（ Formal parameter and actual parameter , Ensure the data stability of sub function and main function , The parameter of the number of subculverts is set to pointer , Data replication is avoided, but the number of subculverts can change the data , Except with const modification .）

Array storage is an equivalent method implemented with pointers ：

 Const Modification to avoid unauthorized modification of the data passed by the main function

Use pointers to pass , Realize the design of multi return value function

 C Language library functions such as strcpy（ ）, Move the mouse over the brackets , You can find that the definition is also a pointer

Pass the return value

Return the public part in the module to , Let the main function hold the “ Handle ”, It is convenient for the program to operate on the specified object

（ The public part here is simply a global variable , Note that it cannot be a local variable , Because at the end of the call , Local variables will be destroyed ）

For example, it is used here GetTime Function to make the main function modifiable Time The data in the array ：

C The language file function creates a file for the specified location , And store the data

 C The language file function reads the file to the specified location , And display data

Directly access the data under the physical address

Access the data in the memory specified by the hardware , Such as equipment ID Number, etc.

RAM Single chip computer at ID distinguish ： 

Single chip microcomputer in program area ID distinguish ： ( Prefix with code Means defined in ROM The address in )

Convert complex format data into bytes , Convenient communication and storage

（ For example, floating point data is transferred when different devices communicate ）

It is not convenient to show the data exchange between different devices , So use different modules in the program to simulate , among AirData It's data sent over the air

General principles ： Convert floating point numbers to char type , Send out byte by byte . Then accept that it will char Turn into float Type to decode , Printout .

Air data module

Send data module

Accept data modules