159 lines
3.9 KiB
Markdown
159 lines
3.9 KiB
Markdown
---
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title: Macros
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TARGET DECK: Obsidian::STEM
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FILE TAGS: c17::macro
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tags:
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- c17
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---
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## Overview
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Macros refer to `#define` directives that specify terms that should be textually replaced by the preprocessor during compilation:
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```c
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#define NAME ...
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```
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For types that don't have literals that describe their constants, we can use **compound literals** on the replacement side of the macro:
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```c
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#define NAME (T){ INIT }
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```
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%%ANKI
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Basic
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What preprocessor directive is used to define macros?
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Back: `#define`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419429-->
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END%%
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%%ANKI
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Basic
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How are compound literals specified in a macro definition, say `MACRO`?
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Back:
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```c
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#define MACRO (T){ INIT }
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```
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419447-->
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END%%
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%%ANKI
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Basic
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What term is used to refer to the replacement side of the following macro?
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```c
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#define MACRO (T){ INIT }
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```
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Back: A compound literal.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419481-->
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END%%
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%%ANKI
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Basic
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What is the difference between the following two lines?
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```c
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#define MACRO (T){ INIT }
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# define MACRO (T){ INIT }
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```
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Back: N/A. They are equivalent.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419485-->
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END%%
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%%ANKI
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Basic
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What is the difference between the following two lines?
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```c
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#define MACRO (T){ INIT }
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#define MACRO(T){ INIT }
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```
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Back: The first defines a compound literal. The latter defines a function-like macro.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419489-->
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END%%
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%%ANKI
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Basic
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What is `T` a reference to in the following compound literal?
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```c
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#define MACRO (T){ INIT }
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```
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Back: A type-specifier.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419492-->
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END%%
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%%ANKI
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Basic
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What is `INIT` a reference to in the following compound literal?
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```c
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#define MACRO (T){ INIT }
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```
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Back: An initializer.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419495-->
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END%%
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%%ANKI
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Basic
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Why aren't compound literals suitable for ICE?
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Back: They are objects, not constants.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419498-->
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END%%
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%%ANKI
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Basic
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How can the following be rewritten so that `MACRO` is an object?
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```c
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#define MACRO 5
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```
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Back:
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```c
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#define MACRO (int){5}
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```
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419500-->
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END%%
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%%ANKI
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Basic
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What is the difference between the following two lines?
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```c
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#define MACRO 5
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#define MACRO (int){5}
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```
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Back: The former is a literal whereas the latter is a compound literal.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419503-->
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END%%
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%%ANKI
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Basic
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Why should compound literals be, generally speaking, `const`-qualified?
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Back: Doing so gives the optimizer more room to generate good binary code.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419506-->
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END%%
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%%ANKI
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Basic
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How do we write macro definitions that span more than one line?
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Back: Ending all but the last line with a `\` character.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419508-->
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END%%
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%%ANKI
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Basic
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Generally speaking, what character should *not* be specified at the end of a macro definition?
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Back: `;`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1727432419511-->
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END%%
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## Bibliography
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* Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020). |