22b4470f2a
Update all links to C++ Core Guidelines to `e49158a`.
Refresh done using the following script and some manual edits:
db76e34e74/personal/fred-tingaud/rspec/refresh-cppcoreguidelines.py
When re-using this script, be mindful that:
- it does not cover `shared_content`
- it does not properly escape inline code in links (e.g., "[=]" or "`mutex`es")
- it does not change `C++` to `{cpp}` in link titles.
Co-authored-by: Marco Borgeaud <marco.borgeaud@sonarsource.com>
81 lines
2.2 KiB
Plaintext
81 lines
2.2 KiB
Plaintext
== Why is this an issue?
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Casting a base-class pointer/reference to a derived-class pointer/reference is commonly referred to as downcasting which can only be done using an explicit cast.
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However, the use of ``++static_cast++`` for such a cast is unsafe because it doesn't do any runtime check. If the cast memory doesn't contain an object of the expected derived type, your program enters the undefined behavior territory.
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If your object is polymorphic, you might prefer using ``++dynamic_cast++`` instead, as it allows safe downcasting by performing a run-time check:
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* If the cast memory contains an object of the expected derived type, the check succeeds. The result of the ``++dynamic_cast++`` points/refers to the derived object.
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* If the cast memory doesn't contain an object of the expected derived type, the check fails. If the ``++dynamic_cast++`` is used on a pointer, ``++nullptr++`` is returned. If it was used on a reference, ``++std::bad_cast++`` is thrown.
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This rule raises an issue when ``++static_cast++`` is used for downcasting.
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=== Noncompliant code example
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[source,cpp]
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----
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struct Shape {
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virtual ~Shape();
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// ...
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};
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struct Rectangle : public Shape {
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double width;
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double height;
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};
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struct Circle : public Shape {
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double radius;
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};
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double computeArea(const Shape* shape) {
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const auto* rectangle = static_cast<const Rectangle*>(shape); // Noncompliant
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return rectangle->width * rectangle->height;
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}
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----
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=== Compliant solution
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[source,cpp]
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----
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struct Shape {
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virtual ~Shape();
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// ...
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};
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struct Rectangle : public Shape {
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double width;
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double height;
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};
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struct Circle : public Shape {
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int radius;
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};
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double computeArea(const Shape* shape) {
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if(const auto* rectangle = dynamic_cast<const Rectangle*>(shape)) { // Compliant
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return rectangle->width * rectangle->height;
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}
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return 0;
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}
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----
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== Resources
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* {cpp} Core Guidelines - https://github.com/isocpp/CppCoreGuidelines/blob/e49158a/CppCoreGuidelines.md#prosafety-type-safety-profile[Type.2: Don’t use `static_cast` to downcast]
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ifdef::env-github,rspecator-view[]
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'''
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== Comments And Links
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(visible only on this page)
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=== relates to: S5823
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endif::env-github,rspecator-view[]
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