Thread: passing struct to function by reference

Hey again another question. How can I pass a struct to a function by reference.

Code:

int myfunction(*)
{
  
  // will do stuff to struct
 return 0;
};

int main()
{

 struct data 
 {
    int a;
    int b;
    int c;
  };

data d;

myfunction(*);]

return 0;
}

This is just example code of course. What is it that I need to put in the place of the *'s? Reading from a book the way to pass a variable by reference is (myVar &hisVar). Is this correct? If not what is. What bit do I need to put where. I am very confused. I may be jumping ahead of myself but I find if I don't try adn get the complicated bits done I get bored and give up. I can wite hello world in lots of languages but can't do anything useful in any of them.

Thanks

Ironfistchamp

Code:

 struct data 
 {
    int a;
    int b;
    int c;
  };

// C-ctyle
int myfunction(struct data* d)
{
  
  // will do stuff to struct
  d->a = 1;
  d->b = 2;
  d->c = 3;
 return 0;
};


// C++ style
int myfunction(data& d)
{
  
  // will do stuff to struct
  d.a = 1;
  d.b = 2;
  d.c = 3;
 return 0;
};


int main()
{

data d;

// C-style
myfunction(&d);

// C++ style
myfunction(d);
return 0;
}

Exceelent that's done the trick thanks. Does it matter having the struct outside main? I was told not to as it is like a variable and you should refrain from making global variables. True or not?

Thanks again

Ironfistchamp

Aha got ya. Ok new problem. I wanted to use my own header (want to get the hang of it and make my code more "modular"). So I put it in myfunc.h, put the #include "myfunc.h" at the top and went from there. But I get the error that the struct is not defined in the scope even though it is global. Why?

Thanks

Ironfistchamp

All I have is the main.cc and myfunc.h files. All the includes are in the main.cc file and the struct is defined right after that. The myfunc.h file only has the function we worked out before. Should be right shouldn't it. You must be able to pass stuff to functions in header files.

I don't know perhaps I have the wrong end of the stick. The book I have (Accelerated C++) is good but you have to really think about what is being said. It has great info but isn't written in a terribly friendly way.

Wow thanks. OK I shall read more about headers. I looked for a tutorial here but couldn't see one dedicated to just headers. Is it included under a different name.


I really want to thank you for your replies. This has got to be one of the best forums. Generally I spend days waiting for some elitest to tell me I am a "n00b" (well not in the Ubuntu forums they rock too )

Thanks again

Ironfistchamp

Originally Posted by ironfistchamp

Exceelent that's done the trick thanks. Does it matter having the struct outside main? I was told not to as it is like a variable and you should refrain from making global variables. True or not?

Thanks again

Ironfistchamp

Not true. Whoever told you that was wrong. structures do nothing more than declare a user-defined data type, it does not create an object of that type. And all data types must be defined before they can be used, so its impossible to use a structure before it is defined. And that is another reason for putting structure definitions in header files. For examples of how it is done just look in the header files that were shipped and installed with your compiler. There is nothing sacred about them and they will not make you go blind if you look directly at them. Pick an easy one, like string.h to see what all it contains.

Ah good idea will do. If I was to put the struct in a header file that would be a good use for my own headers right?

Thanks again

Ironfistchamp