treewide: replace include guards with pragma once #253
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
An alternative to include guards using `#ifndef`, `#define` and `#endif` is `#pragma once`. This non-standard but commonly supported directive among C and C++ compilers, it also requires less code and does not require the definition of a variable with risk of name conflicts. Also, the variable definitions often deviate after file renaming and/or move. Bonus, the use of `#pragma once` may improve compilation speed since it is a higher-level mechanism. The compiler itself can compare filenames or inodes without having to invoke the C preprocessor to resolve `#ifndef` and `#endif`. Signed-off-by: Robin Jarry <[email protected]>
christophefontaine
approved these changes
Jul 3, 2025
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
An alternative to include guards using
#ifndef,#defineand#endifis#pragma once. This non-standard but commonly supported directive among C and C++ compilers, it also requires less code and does not require the definition of a variable with risk of name conflicts. Also, the variable definitions often deviate after file renaming and/or move.Bonus, the use of
#pragma oncemay improve compilation speed since it is a higher-level mechanism. The compiler itself can compare filenames or inodes without having to invoke the C preprocessor to resolve#ifndefand#endif.