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Notes on pointers.

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Joshua Potter 2024-11-23 15:21:18 -07:00
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title: "2024-11-23"
---
- [ ] Anki Flashcards
- [x] Anki Flashcards
- [x] KoL
- [x] OGS
- [ ] Sheet Music (10 min.)
- [ ] Korean (Read 1 Story)
- [ ] Korean (Read 1 Story)
* Notes on Apostol's axiomatic definition of [[area]].
* More notes on [[derived#Pointers|pointers]].

2
notes/algorithms/order-growth.md
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@ -440,7 +440,7 @@ END%%
%%ANKI
Basic
What is the transpose symmetric property of $\Theta$-notation?
Back: N/A
Back: N/A.
Reference: Thomas H. Cormen et al., Introduction to Algorithms, Fourth edition (Cambridge, Massachusett: The MIT Press, 2022).
<!--ID: 1709752223322-->
END%%

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@ -136,6 +136,8 @@ Tags: printf
<!--ID: 1708425941269-->
END%%
### Flags
| Flag | Description |
| ---- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| `-` | Left-aligns the output |
@ -400,6 +402,8 @@ Tags: printf
<!--ID: 1710673807990-->
END%%
### Length
Length | Description
--------- | -----------
`hh` | `int` sized integer argument promoted from a `char`
@ -457,6 +461,8 @@ Tags: printf
<!--ID: 1708426673725-->
END%%
### Specifiers
Specifier | Description
--------- | -----------
`d`, `i` | a decimal `signed int`
@ -960,6 +966,15 @@ Tags: printf
<!--ID: 1707852083126-->
END%%
%%ANKI
Basic
What should be done to a pointer outputted by the `%p` format specifier?
Back: It should be cast to a `void*` pointer.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
Tags: printf
<!--ID: 1732397726966-->
END%%
%%ANKI
Basic
Given `int64_t x`, why is `printf("%d", x)` a problem?

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notes/c17/typedefs.md
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@ -103,6 +103,40 @@ Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70
<!--ID: 1730740461662-->
END%%
%%ANKI
Basic
When can two pointers be subtracted?
Back: Only if both refer to elements of the same array object.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726963-->
END%%
%%ANKI
Basic
What is the result of `p - q` in the following?
```c
double A[4] = { 0.0, 1.0, 2.0, -3.0 };
double* p = &A[1];
double* q = &A[3];
```
Back: `-2`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726964-->
END%%
%%ANKI
Basic
What is the result of `p - q` in the following?
```c
double A[4] = { 0.0, 1.0, 2.0, -3.0 };
double* p = &A[3];
double* q = &A[1];
```
Back: `2`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726965-->
END%%
%%ANKI
Basic
Is `size_t` signed or unsigned?

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@ -1133,6 +1133,143 @@ Reference: Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Program
<!--ID: 1731942192229-->
END%%
%%ANKI
Basic
Trap representations are most relevant to what kind of derivied type?
Back: Pointers.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726948-->
END%%
%%ANKI
Basic
What does a trap representation refer to?
Back: An invalid interpretation of a bit pattern as a specific type.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726951-->
END%%
%%ANKI
Basic
What happens when accessing an object with a trap representation of its type?
Back: Undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726952-->
END%%
%%ANKI
Basic
*Why* must a dereferenced object have the correct designated type?
Back: A trap representation of an object's type leads to undefined behavior.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726953-->
END%%
%%ANKI
Basic
Refer to the following. *Why* isn't the pointer addition considered correct?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[0] + 2;
```
Back: N/A. It is.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726954-->
END%%
%%ANKI
Basic
Refer to the following. *Why* isn't the pointer addition considered correct?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[0] + 3;
```
Back: Pointers cannot refer to addresses beyond that immediately following the array.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726955-->
END%%
%%ANKI
Basic
Refer to the following. What values of `N` yield a valid pointer assignment?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[N];
```
Back: `0`, `1`, and `2`.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726956-->
END%%
%%ANKI
Basic
Refer to the following. What is the first value of `N` that yields an invalid pointer assignment?
```c
double A[2] = { 0.0, 1.0 };
double* p = &A[N];
```
Back: `3`
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726957-->
END%%
%%ANKI
Basic
Refer to the following. Is the last line a valid dereference?
```c
double A[2] = { 0.0, 1.0 };
double a = *(&A[1]);
```
Back: Yes.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726958-->
END%%
%%ANKI
Basic
Refer to the following. Is the last line a valid dereference?
```c
double A[2] = { 0.0, 1.0 };
double a = *(&A[2]);
```
Back: No.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726959-->
END%%
%%ANKI
Cloze
A pointer must point to a {valid object}, or {one position beyond} a valid object, or be {null}.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726960-->
END%%
%%ANKI
Basic
Consider the following. At what point *could* the program crash?
```c
double A[] = { 0.0, 1.0 };
double* p = &A[0] + 2;
double q = *p;
```
Back: On the third line.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726961-->
END%%
%%ANKI
Basic
Consider the following. At what point *could* the program crash?
```c
double A[] = { 0.0, 1.0 };
double* p = &A[0] + 3;
double q = *p;
```
Back: On the second line.
Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
<!--ID: 1732397726962-->
END%%
## Bibliography
* 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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---
title: Geometry
TARGET DECK: Obsidian::STEM
FILE TAGS: geometry
tags:
- geometry
---
## Overview