Pointers have the same size as the machine's word size since it should be able to refer to any virtual address. All pointers are either **valid**, **null**, or **indeterminate**.
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Basic
*Why* does a pointer's size match the machine's word size?
Back: Because it should be able to refer to any virtual address.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
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END%%
%%ANKI
Basic
How is `(*r).field` more compactly written?
Back: `r->field`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
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END%%
%%ANKI
Basic
How many members *must* be defined in a `struct` initializer?
C allows arithmetic on pointers, where the computed value is scaled according to the size of the data type referenced by the pointer.
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Basic
How is the following (assumed valid) expression simplified?
```c
*&E
```
Back: As just `E`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461664-->
END%%
%%ANKI
Basic
How is the following (assumed valid) expression simplified?
```c
&*E
```
Back: As just `E`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461665-->
END%%
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Cloze
Pointer arithmetic {`*(A + i)`} is equivalent to array reference `A[i]`.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730740461666-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[3][4];
return A[1][2];
}
```
Back: `return *(A + 6);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799783-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[3][4];
return A[2][0];
}
```
Back: `return *(A + 8);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799787-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[4][3];
return A[1][2];
}
```
Back: `return *(A + 5);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799789-->
END%%
%%ANKI
Basic
How do we rewrite the return statement using pointer arithmetic?
```c
int func() {
int A[4][3];
return A[1][0];
}
```
Back: `return *(A + 3);`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1730745799791-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int* func(int *E) { return E; }
```
Back:
```asm
movq %rdi,%rax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461667-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int func(int *E) { return E[0]; }
```
Back:
```asm
movl (%rdi),%eax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461668-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int func(int *E, int i) { return E[i]; }
```
Back:
```asm
movl (%rdi, %rsi, 4),%eax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461669-->
END%%
%%ANKI
Basic
How is the `return` statement likely translated to x86-64?
```c
int* func(int *E) { return &E[2]; }
```
Back:
```asm
leaq 8(%rdi),%rax
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
Tags: x86-64
<!--ID: 1730740461670-->
END%%
%%ANKI
Basic
Suppose `char *p` has address `S`. What is the result of the following?
```c
(int *) p + 7
```
Back: `S + 28`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192201-->
END%%
%%ANKI
Basic
Suppose `char *p` has address `S`. What is the result of the following?
```c
(int *) (p + 7)
```
Back: `S + 7`
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192210-->
END%%
%%ANKI
Basic
How do we declare a function pointer `fp` to the following?
```c
int foo(int x, int *p);
```
Back:
```c
int (*fp)(int, int *);
```
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192213-->
END%%
%%ANKI
Basic
What do the following two lines declare instances of?
```c
int (*fp)(int, int *);
int *fp(int, int *);
```
Back: The first is a function pointer. The second is a function.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
<!--ID: 1731942192218-->
END%%
%%ANKI
Basic
What is the value of a function pointer?
Back: The address of the first instruction in the function's machine-code representation.
Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
The `NULL` macro refers to a **null pointer constant**, an ICE with value `0` or such an expression cast to type `void*`. The following table lists some valid values `NULL` can take on:
Accessing the same object through different pointers is called **aliasing**. With the exclusion of [[simple#Character Types|character types]], only pointers of the same base type may alias.
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Basic
What does aliasing refer to?
Back: Accessing the same object through different pointers.
