What does void (* const ivt[])(void) mean?-CodePudding

I'm reading the book Embedded Systems Architecture by Daniele Lacamera. In Chapter 4,The Boot-Up code

__attribute__ ((section(".isr_vector"))) void (* const ivt[])(void) =
{
    (void (*) (void))(END_STACK),
    isr_reset,
    //...
};

I don't understading void (* const ivt[])(void), is it the array? If it's the array what does (void) mean?

CodePudding user response：

Install the tool cdecl and ask it to explain things to you:

mrvn@ryzen:~$ cdecl
Type `help' or `?' for help
cdecl> explain void (* const ivt[])(void)
declare ivt as array of const pointer to function (void) returning void

CodePudding user response：

It is an array named ivt holding constant pointers to functions that take no parameters and return void.

CodePudding user response：

i dot't understading void (* const ivt[])(void), is it the array?

Yes, ivt is an array of constant pointers to function that accepts no arguments and returns nothing.

The type of elements of ivt array is

 void (* const)(void)

which means constant pointer to function which accepts no arguments and returns nothing.

If it's the array what does (void) mean?

It means function accepts no arguments.

CodePudding user response：

ivt is an array of constant pointers to functions that takes no parameters and have the return type void.

Perhaps an example might help understand the situation better:

void func1()
{
    std::cout<<"func1 called"<<std::endl;
}
void func2()
{
    std::cout<<"func2 called"<<std::endl;
}
void foo()
{
    std::cout<<"foo called"<<std::endl;
}

void foobar()
{
    
}
int main()
{
//----------------vvv---------------------------------> ivt is an array of const pointers to a function with return type of void and having 0 parameters
    void (* const ivt[])(void) = {func1, func2, foo};  
//--------------------------------^^^^^--^^^^^--^^^---> add pointers  to these 3 functions into the array 


   //iterate through the elements in the array and call the member functinos 
   for(void (*const PTR)(void): ivt)
   {
       PTR();
       
//-----------v---------------------------------------->this assignment won't work because pointers are themselves const so you can make them point to another function
       //PTR = foobar; 
   }
    
}