ishangsf/rspec
2
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Modify rule S1003: Update description CPP-5404 (#4016)

Browse Source
This commit is contained in:
Marco Borgeaud 2024-07-10 10:08:40 +02:00 committed by GitHub
parent 0fd7e2c4b0
commit 4b2ab1f46d
No known key found for this signature in database
GPG Key ID: B5690EEEBB952194
1 changed files with 14 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
rules/S1003/cfamily/rule.adoc
View File

@ -1,13 +1,12 @@
== Why is this an issue?
A using directive makes names from another namespace available in the current scope. It should only be used when those names do not create an ambiguity with other names, otherwise, it is better to fully qualify the names you want to use.
A using-directive (e.g., `using namespace std;`) makes names from another namespace available in the current scope. It should only be used when those names do not create an ambiguity with other names. Otherwise, it is better to fully qualify the names you want to use.
The effect of using-directives inside a function body ceases at the end of the current scope. However, when the using-directives are at the global or namespace scope, their effects propagate to the rest of the scope.
When you write a header file, you don't know from which context it will be included. Therefore, if this header contains using directives, you cannot be sure that they will not create ambiguities in that context. Those ambiguities could lead to compilation failures or, worse, to a different function being selected by overload resolution depending on the order of inclusion of headers.
A using declaration behaves in the same way but only for one name. Because of their much narrower scope, this rule does not apply to using declarations.
When you write a header file, you don't know from which contexts it will be included. Therefore, if this header contains using-directives at the global or namespace scope, you cannot be sure that they will not create ambiguities in some of the including contexts. Those ambiguities could lead to compilation failures or, worse, to a different function being selected by overload resolution depending on the order of inclusion of headers.
This rule will raise an issue on using-directives in header files.
=== Noncompliant code example
@ -52,12 +51,21 @@ void m2 ( )
=== Exceptions
The issue only happens if the using directive is at global scope or at namespace scope. If is is inside a function body, it will cease to be in effect at the end of the current scope, and will not propagate to the users of the header file.
Using-declarations (e.g., `using std::cout;`) behave in the same way but only for one name. This rule does not apply to them because their scope is much narrower.
Additionally, since it isn't easy to fully qualify the content of the `std::literals` and `std::placeholders` namespaces, this rule doesn't raise violations for using-directives that target these namespaces or their sub-namespaces, such as ``++std::literals::chrono_literals++``.
== Resources
=== Documentation
* {cpp} reference - https://en.cppreference.com/w/cpp/language/namespace#Using-directives[using-directives]
=== External coding guidelines
* MISRA {cpp}:2008, 7-3-6 - using-directives and using-declarations (excluding class scope or function scope using-declarations) shall not be used in header files.
* {cpp} Core Guidelines - https://github.com/isocpp/CppCoreGuidelines/blob/e49158a/CppCoreGuidelines.md#sf7-dont-write-using-namespace-at-global-scope-in-a-header-file[SF.7: Don't write `using namespace` at global scope in a header file]