Reference & Pointer in C(PP)

“Reference & Pointer in C” expressed in English.

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Forword

The reason why I write this blog article is just to understand the reference and pointer completely.Let’s have a look the underlying implementation of the reference and pointer.

Music

天净沙 By 骆集益/周志华

In one word

Reference is the same as pointer in essence.Both are the address,and the differences between both are the using rules.

Body

There are some situations:

• Basic data type reference
• Struct type reference
• Class type reference
• Class type pointer
• About the segment

We will talk it in the above way.

0x01 Basic data type reference

There are two programs in this situation.

• Let’s see the reference and pointer in underlying assembly code :-)

In this program,we can conclude these results:

1. The local variables is saved in the address begining with %rbp-0x24(to increasing direction.).The int type variables cover 4 bytes and the address type variables cover 8 bytes.

   1. Variable a is saved at %rbp-0x24
   2. Variable b is saved at %rbp-0x20
   3. Variable c is saved at %rbp-0x18
   4. Variable d is saved at %rbp-0x10

2. The reference and the pointer both are address.

• Let’s see the instance of reference in calling functions.

We can conclude these results:

1. Call-by-reference relays the parameters by their address.
2. We have known that we can call by value.Of course,the address is also a value.Thus,we can think that there is only call-by-value.

0x02 Struct type reference

Let’s talk about reference in struct type variables.

In this program,we can conclude that:

1. The variables defined in the way - T a; - are all saved in the stack frame.
2. The reference of struct-type variables is also an address.

0x03 Class type reference

The class-type instance is the same as the struct.

It’s easy! You can jump it!

0x04 Class type pointer

Let’s have a look at the instance defined by new:

We can conclude that the pointer is just the address points to the heap somewhere.Of course,the address in the heap is undefined,because it’s dynamic and the assembly code is objdump by gcc -c(Compile and assemble, but do not link)

0x05 About the segment

In the situation,I want to have a look at the global variables,but I don’t find it in the assembly code.It’s in the data segment!

Let’s retrospect the segment partition:

Conclusion

In the article,we explore the underlying assembly code of reference and pointer,and we review the segment partition.Hope you can get a lot.

Have a nice day.
Bye!
-:)