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>
99 lines
2.4 KiB
Plaintext
99 lines
2.4 KiB
Plaintext
== Why is this an issue?
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Class members are initialized in the order in which they are declared in the class,
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not the order in which they appear in the class initializer list.
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To avoid errors caused by order-dependent initialization,
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the order of members in the initialization list should match the order in which members are declared in a class.
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The initialization order, as described https://en.cppreference.com/w/cpp/language/constructor#Initialization_order[here], is:
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. If the constructor is for the most-derived class, virtual bases are initialized in the order in which they appear in depth-first left-to-right traversal of the base class declarations (left-to-right refers to the appearance in base-specifier lists)
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. Then, direct bases are initialized in left-to-right order as they appear in this class's base-specifier list
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. Then, non-static data members are initialized in order of declaration in the class definition.
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=== Noncompliant code example
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[source,cpp]
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----
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#include <iostream>
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struct A {
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A(int num) {
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std::cout << "A(num = " << num << ")" << std::endl;
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}
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};
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struct B {
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int b;
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};
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class C : public A, B {
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public:
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int x;
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int y;
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C(int i) : B{i}, A{b}, y(i), x(y + 1) { } // Noncompliant
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};
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int main() {
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C c(1); // Undefined behavior, might print "A(num = 0)"
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std::cout << c.x << " " << c.y << std::endl; // might print "1 1"
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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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#include <iostream>
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struct A {
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A(int num) {
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std::cout << "A(num = " << num << ")" << std::endl;
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}
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};
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struct B {
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int b;
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};
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class C : public A, B {
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public:
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int x;
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int y;
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C(int i) : A{i}, B{i}, x(i + 1), y(i) { }
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};
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int main() {
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C c(1); // prints "A(num = 1)"
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std::cout << c.x << " " << c.y << std::endl; // prints "2 1"
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}
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----
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== Resources
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* https://wiki.sei.cmu.edu/confluence/x/dXw-BQ[CERT, OOP53-CPP.] - Write constructor member initializers in the canonical order
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* {cpp} Core Guidelines - https://github.com/isocpp/CppCoreGuidelines/blob/e49158a/CppCoreGuidelines.md#c47-define-and-initialize-member-variables-in-the-order-of-member-declaration[C.47: Define and initialize member variables in the order of member declaration]
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Reorder these initializers to match their declaration order.
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'''
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== Comments And Links
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(visible only on this page)
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=== is duplicated by: S1266
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endif::env-github,rspecator-view[]
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