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---
title: Strings
TARGET DECK: Obsidian::STEM
FILE TAGS: c
tags:
- c
---
## Overview
A contiguous sequence of characters terminated by the `NUL` character (refer to [[ascii|ASCII]]). Text data is said to be more platform-independent than [[endianness|binary]] data since it is unaffected by word size or byte ordering.
%%ANKI
Basic
What is a C-style string?
Back: A character array terminated with a `NUL` character.
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
What character terminates all C-style strings?
Back: `NUL`
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
What is the decimal value of `NUL` in ASCII encoding?
Back: `0`
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
Text is more platform-independent than binary because it is unaffected by what two properties?
Back: Word size and byte ordering.
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%%
## `printf`
The syntax for the format placeholder is `%[flags][width][.precision][length]specifier`.
Flag | Description
--------- | -----------
`-` | Left-aligns the output
`+` | Prepends a plus for positive signed-numeric types
`␣` | Prepends a space for positive signed-numeric types
`0` | Prepends zeros for numeric types
%%ANKI
Cloze
The {`-`} flag {left-aligns the output}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
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END%%
%%ANKI
Basic
The `-` flag overrides what default behavior?
Back: Output is right-aligned by default.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
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END%%
%%ANKI
Cloze
The {`+`} flag {prepends a plus for positive signed-numeric types}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
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END%%
%%ANKI
Basic
The `+` flag overrides what default behavior?
Back: Nothing is prepended to positive signed-numeric types by default.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
<!--ID: 1707918756852-->
END%%
%%ANKI
Cloze
The {`␣`} flag {prepends a space for positive signed-numeric types}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
<!--ID: 1707918756856-->
END%%
%%ANKI
Basic
The `␣` flag overrides what default behavior?
Back: Nothing is prepended to positive signed-numeric types by default.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
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END%%
%%ANKI
Basic
How do the `+` and `␣` flags relate to one another?
Back: Both prepend a character to positive signed-numeric types.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
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END%%
%%ANKI
Basic
What happens if both the `+` and `␣` flags are specified?
Back: The `+` flag takes precedence.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
<!--ID: 1707918756870-->
END%%
%%ANKI
Cloze
The {`0`} flag {prepends zeros for numeric types}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
<!--ID: 1707918756875-->
END%%
%%ANKI
Basic
What option must be specified for the `0` flag to take effect?
Back: The "width" option.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
<!--ID: 1707918756881-->
END%%
%%ANKI
Basic
The `0` flag overrides what default behavior?
Back: Spaces are used to match the "width" option by default.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
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END%%
Specifier | Description
--------- | -----------
`d`, `i` | a decimal `signed int`
`u` | a decimal `unsigned int`
`x` | a hexadecimal `unsigned int` (lowercase)
`X` | a hexadecimal `unsigned int` (uppercase)
`o` | an octal `unsigned int`
`s` | a `NUL`-terminated string
`c` | a `char` character
`p` | `void*` address in an implementation-defined format
%%ANKI
Basic
What character do `printf` format specifiers start with?
Back: `%`
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
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END%%
%%ANKI
Basic
Why is `printf` named the way it is?
Back: It stands for **print f**ormatted.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
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END%%
%%ANKI
Cloze
The {`d` and `i`} format specifer(s) output a(n) {decimal `signed int`}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
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END%%
%%ANKI
Cloze
{`d` and `i`} are to `signed` as {`u`} is to `unsigned`.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083044-->
END%%
%%ANKI
Cloze
The {`u`} format specifier(s) output a(n) {decimal `unsigned int`}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083047-->
END%%
%%ANKI
Basic
What distinguishes format specifiers `d` and `i`?
Back: Nothing.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083050-->
END%%
%%ANKI
Basic
Which format specifier(s) were probably used to yield `printf` output `-12`?
Back: `d` or `i`
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083054-->
END%%
%%ANKI
Basic
What distinguishes format specifiers `d` and `u`?
Back: The former is for signed integers, the latter unsigned.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083058-->
END%%
%%ANKI
Cloze
The {`x`} format specifier(s) output a(n) {lowercase hexadecimal `unsigned int`}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083063-->
END%%
%%ANKI
Basic
Which format specifier(s) were probably used to yield `printf` output `7af`?
Back: `x`
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083068-->
END%%
%%ANKI
Cloze
The {`X`} format specifier(s) output a(n) {uppercase hexadecimal `unsigned int`}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083074-->
END%%
%%ANKI
Basic
Which format specifier(s) were probably used to yield `printf` output `7AF`?
Back: `X`
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083080-->
END%%
%%ANKI
Basic
What distinguishes format specifiers `x` and `X`?
Back: The former outputs lowercase hex digits, the latter uppercase.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083086-->
END%%
%%ANKI
Cloze
The {`o`} format specifier(s) output a(n) {octal `unsigned int`}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083091-->
END%%
%%ANKI
Basic
Why doesn't the `o` format specifier have a corresponding `O` specifier?
Back: There is no distinction between lower and uppercase octal digits.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083096-->
END%%
%%ANKI
Cloze
The {`s`} format specifier(s) output a(n) {`NUL`-terminated string}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083100-->
END%%
%%ANKI
Basic
Which format specifier(s) were probably used to yield `printf` output `abc`?
Back: `s`
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083105-->
END%%
%%ANKI
Cloze
The {`c`} format specifier(s) output a(n) {`char` character}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083109-->
END%%
%%ANKI
Basic
Which format specifier(s) were probably used to yield `printf` output `a`?
Back: `c`
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083113-->
END%%
%%ANKI
Cloze
The {`p`} format specifier(s) output a(n) {`void*` address}.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083117-->
END%%
%%ANKI
Basic
Which format specifier(s) were probably used to yield `printf` output `0b80000000`?
Back: `p`
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083121-->
END%%
%%ANKI
Basic
How is the address outputted by the `p` format specifier written?
Back: In an implementation-specific way.
Reference: “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
Tags: printf
<!--ID: 1707852083126-->
END%%
## References
* Bryant, Randal E., and David O'Hallaron. *Computer Systems: A Programmer's Perspective*. Third edition, Global edition. Always Learning. Pearson, 2016.
* “Printf,” in *Wikipedia*, January 18, 2024, [https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962](https://en.wikipedia.org/w/index.php?title=Printf&oldid=1196716962).
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