KEIL multi-file processing in the same project

First, we need a new document. There are two ways to create this document (taking the delay1s function as an example). The first way is to create a delay1s.txt in the project directory and rename it to delay1s.h. Because they are all in the same encoding, there will be no garbled characters, and then open it in the project. The second way is to create a new document directly in the project, and then save it as delay1s.h. If you need to add a lot of files, it is recommended to use the first method. This is my personal suggestion. Secondly, we need to write the content of the delay1s.h file, the content is as follows:

#ifndef _DELAY1S_H_
#define _DELAY1S_H_
void delay1s(); //delay function
#endif
   This is the definition of the header file, which declares the delay1s() function. If we need to use the delay1s() function in other functions, an error will occur during compilation if it is not declared in advance. For #ifndef...#define...#endif; this structure roughly means that if a string is not defined (macro definition), then we define it and then execute the following statements. If it is defined, then skip and do not execute any statements.
   Why do we use such a definition method? For example, in the led_on() function, we call the delay1s() function, and then in the main() function, we also call the delay() function. Then, in the led_on() function, we need to include the header file delay1s.h, and then in the main() function, we also need to include delay1s.h. If we have called led_on() in the main function, then when we encounter delay1s() and led_on() during compilation, delay1s.h will be interpreted twice, and an error will occur. If there is the above preprocessing command, then the _DELAY1S_H_ has been defined the second time, so there will be no problem of repeated definition. This is its role. But note that the header file does not participate in the compilation when the compiler is compiling.
Again, we create a led_on.h, and the code content is as follows:
#ifndef _LED_ON_H_
#define _LED_ON_H_
void led_on(void);//Light flashes
#endif
The role is the same as delay1s.h. If you don't understand, you can look at the above explanation again.
Finally, we complete the three functions we mentioned above.
In the led_on() function, we used the definitions of some registers of the 51 MCU, so we have to include reg52.h, and we used the delay1s() function, so we have to include delay1s.h, so the code of the led_on.c file is as follows:
#include
#include “delay1s.h” //Note that there is no semicolon here
void led_on(void)
{
P0=0x00;
delay1s();
P0=0xff;
delay1s();
}
The code of the Main function is as follows:
#include
#include “delay1s.h”

#include “led_on.h”
void main()
{
led_on();
delay1s();
led_on();

}
In this function, in order to explain the definition of the structure #ifndef...#define...#endif again, you can remove this structure from all .h files, and then compile it to see the effect.
At this point, I believe everyone has a general understanding of this modular writing method. If we want to add new functions, such as adding a running light function, then we only need to add a led_circle.c and led_circle.h, and then follow the above steps to add it to the project. The rest of the program does not need to be changed. Obviously this is very convenient. In fact, the extern keyword can be used for function declarations. This type is the default in C language, so it is not necessary to write it.