What is the difference between callback functions and ordinary functions?

Normal The difference between function and callback function:

Call to a normal function: After the calling program issues a call to the normal function , the program execution immediately switches to the called function until the called function completes execution, and then returns to the calling program to continue execution. From the perspective of the calling program, this process is "Call --> Wait for the called function to complete --> Continue execution"

Call the callback function: The calling program issues a call to the callback function After that, without waiting for the function to complete execution, it returns immediately and continues execution. In this way, the calling program and the called function are executed at the same time. When the called function completes execution, the called function will in turn call a pre-specified function to notify the calling program that the function call has ended. This process is called callback (Callback), which is where the name of the callback function comes from.

Ordinary functions and callback functions are called by other functions. The difference lies in whether the caller knows exactly what he is calling. For example:
void func1(){}
void func2(){}
typedef void (*fp)();//DeclarationFunction pointer, fp represents a null parameter and returns a function pointer of type void
void funcCaller1() {
//Here func1 can be regarded as a normal function
func1();//Here, funcCall1 clearly knows that it has called func1
}
void funcCaller2(fp funcPtr){
funcPtr();//Here, funcCall2 does not know what it is calling. It only knows that it has called a function with empty parameters and a return type of void
}
void funcCaller3(){
//Here, funcCaller2 is an ordinary function, func1 is a callback function
funcCaller2(func1);//Call funcCaller2, the parameter is func1
//Here, funcCaller2 is an ordinary function, func2 is a callback function
funcCaller2(func2);//Call funcCaller2, the parameter is func2
}

The above is the detailed content of What is the difference between callback functions and ordinary functions?. For more information, please follow other related articles on the PHP Chinese website!