2024-11-05 18:32:35 +00:00
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---
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title: Typedefs
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TARGET DECK: Obsidian::STEM
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FILE TAGS: c17::type
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tags:
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- c17
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---
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## Overview
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The `<stddef.h>` header defines a few standard `typedef`s:
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* `ptrdiff_t`: the signed integer type of the result of subtracting two pointers.
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* `size_t`: the unsigned integer type of the result of the `sizeof` operator.
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The standard often uses `typedef`s ending with `_t`.
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%%ANKI
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Basic
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What is the type of `x` in the following?
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```c
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#define int_ptr int *
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int_ptr x, y;
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```
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Back: `int *`
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Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
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<!--ID: 1722786892109-->
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END%%
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%%ANKI
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Basic
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What is the type of `y` in the following?
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```c
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#define int_ptr int *
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int_ptr x, y;
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```
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Back: `int`
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Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
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<!--ID: 1722786892110-->
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END%%
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%%ANKI
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Basic
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What is the type of `x` in the following?
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```c
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typedef int_ptr int *
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int_ptr x, y;
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```
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Back: `int *`
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Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
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<!--ID: 1722786892111-->
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END%%
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%%ANKI
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Basic
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What is the type of `y` in the following?
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```c
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typedef int_ptr int *
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int_ptr x, y;
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```
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Back: `int *`
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Reference: Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
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<!--ID: 1722786892112-->
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END%%
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%%ANKI
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Basic
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What header defines `size_t`?
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Back: `<stddef.h>`
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Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
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<!--ID: 1730740461658-->
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END%%
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%%ANKI
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Basic
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What header defines `ptrdiff_t`?
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Back: `<stddef.h>`
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Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
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<!--ID: 1730740461659-->
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END%%
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%%ANKI
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Basic
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`ptrdiff_t` is used as the type of what result?
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Back: Subtracting two pointers.
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Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
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<!--ID: 1730740461660-->
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END%%
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%%ANKI
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Basic
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`size_t` is used as the type of what result?
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Back: The `sizeof` operation.
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Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
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<!--ID: 1730740461661-->
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END%%
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%%ANKI
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Basic
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Is `ptrdiff_t` signed or unsigned?
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Back: Signed.
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Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
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<!--ID: 1730740461662-->
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END%%
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2024-11-23 22:21:18 +00:00
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%%ANKI
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Basic
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When can two pointers be subtracted?
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Back: Only if both refer to elements of the same array object.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732397726963-->
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END%%
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%%ANKI
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Basic
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What is the result of `p - q` in the following?
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```c
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double A[4] = { 0.0, 1.0, 2.0, -3.0 };
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double* p = &A[1];
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double* q = &A[3];
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```
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Back: `-2`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732397726964-->
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END%%
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%%ANKI
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Basic
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What is the result of `p - q` in the following?
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```c
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double A[4] = { 0.0, 1.0, 2.0, -3.0 };
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double* p = &A[3];
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double* q = &A[1];
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```
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Back: `2`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732397726965-->
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END%%
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2024-11-05 18:32:35 +00:00
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%%ANKI
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Basic
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Is `size_t` signed or unsigned?
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Back: Unsigned.
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Reference: “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
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<!--ID: 1730740461663-->
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END%%
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%%ANKI
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Basic
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The C standard typically suffixes `typedef`s with what?
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Back: `_t`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1730758755507-->
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END%%
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## Bibliography
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* “ISO: Programming Languages - C,” April 12, 2011, [https://port70.net/~nsz/c/c11/n1570.pdf](https://port70.net/~nsz/c/c11/n1570.pdf).
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* Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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* Van der Linden, Peter. _Expert C Programming: Deep C Secrets_. Programming Languages / C. Mountain View, Cal.: SunSoft Pr, 1994.
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