[C syntax] void*

void, Very common , I don't think it's wrong to understand it as empty （ Generally, only () In fact, it doesn't represent (void), The former can be empty , The latter must be empty ）
void*, Library functions are also common , I didn't use it myself , It has always been understood as a null pointer , These two days I know quite a deviation , In fact, it is called universal pointer , It is only empty when uninitialized , It must be awkward to call null pointer after initialization , After all, the content is not empty , Null is the pointer type , Instead of pointer value .

• What is a general pointer ？
  seeing the name of a thing one thinks of its function , Is a general pointer , There is no type in itself , The type is empty , The content can not be empty , Any other pointer can be assigned to it , Without warning , So it is called universal pointer ( stay gcc11.2 in , It is assigned to other pointers without warning , But don't use it like this ).

Because of the special type , Therefore, when quoting, it is necessary to forcibly convert to the corresponding type before quoting , Although it can also be directly assigned to the actual pointer of the same type when assigning values (gcc11.2 By default, there is no warning ,clangd LSP The server cannot detect the error ), But it's not recommended . Cast can trigger type checking when the compiler assigns pointer types , So it's best to turn strongly before using , Here is a sample program and running results ：

#include "stdio.h"
#include "stdlib.h"

int main(void)
{
    
	char a = 2;
	char *p = &a;
	void* vp = NULL;
	char *pc = NULL;
	
	vp = p; 								//char* The pointer is directly assigned to the general pointer 
	*(char*)vp = 1;  				 		// The general pointer can also be referenced after strong rotation 
	p = (char*)vp;                          // In fact, direct assignment can also , But it's safer after strong rotation , Otherwise, there is no type check for pointer assignment  
	printf("%d, %d",*(char*)vp, *p);       // When printing, you can see that the general pointer reference is normal 
	pc = (char*)malloc(100*sizeof(char));  // The returned generic pointer is usually cast , It is already the default writing 
	free(pc);
	getchar();
	return 0;
}

Standard library functions are heavily used void*, such as C Memory management provided by language , Look again and you will understand why you use void* 了 ：

// Apply for fixed size memory 
void *malloc(int num); 
// Memory free 
void free(void *address);