C callback function, interface function pointer as function parameter, function pointer as structure member

First statement , This is C Usage of ,C++ We should put an end to it ;

There are two common uses of function pointers ：

1. One is as a member of a structure ;

2. The function pointer is used as the parameter of the function ;

The meaning of the two methods is interface ,C It's also called Callback function ;

Function pointer declaration ：

typedef int (*objFunction_ptr)(int inValue) ;

 // Callback function （ Function implementation ）

int  objFunction(int inValue)
{
    // You want to adjust the parameters   How to deal with ; This similar interface ; It may also be the result returned ;
    int cur= inValue+10;
    return cur;
}

One 、 Function pointers act on structural members

// Structure

typedef struct FounctionStruct{
        int a;
        objFunction_ptr callback;
}FOUND_STRUCT;

 // Structure passes in function

int GetMessage(int curValue,FounctionStruct & func)
{

   curValue+= func.a;
   return func.callback(curValue);
}

// Test code

int main(int argc, char *argv[])
{
    int curValue = 100;
 
    FounctionStruct func;
      func.a = 20;
      func.callback = &objFunction;
      int tar =  GetMessage(curValue,func);
    return 0;
}

result tar =130;

That's it , Callback ; So you can get , The result returned , You can also weight the results , Encrypted , Something about yourself ;

Two 、 Function pointer as Function parameter

// function ：

int GetMessageFun(int curValue,objFunction_ptr  callback)
{
    curValue += 100;
    return callback(curValue);
}

// Call tests ;

int main(int argc, char *argv[])
{
    int curValue = 100;
  
    objFunction_ptr fun = & objFunction;
    int tarValue = GetMessageFun(curValue,fun);
    return 0;
}

result

tarValue=210;

That's it , Callback ; So you can get , The result returned , You can also weight the results , Encrypted , Something about yourself ;