C++ attribute: deprecated (since C++14)

 

C++

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C++ language

General topics
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Declarations

Overview declaration syntax decl-specifier-seq declarator Specifiers typedef inline virtual function specifier explicit function specifier    friend constexpr (C++11) consteval (C++20) constinit (C++20) storage class specifiers translation-unit-local (C++20) class/struct union enum decltype (C++11) auto (C++11) alignas (C++11) constvolatile elaborated type specifier attributes (C++11)

Declarators reference pointer array Block declarations simple-declaration → structured binding declaration (C++17) alias declaration(C++11) namespace alias definition using-declaration using-directive static_assert declaration (C++11) asm-declaration opaque enum declaration(C++11) Other declarations namespace definition function declaration class template declaration function template declaration explicit template instantiation(C++11) explicit template specialization linkage specification attribute declaration (C++11) empty declaration

 

Attributes

noreturn‎ (C++11)

carries_dependency (C++11)

deprecated (C++14)

fallthrough (C++17)

nodiscard (C++17)

maybe_unused (C++17)

likelyunlikely (C++20)(C++20)

no_unique_address (C++20)

optimize_for_synchronized (TM TS)

 

Indicates that the name or entity declared with this attribute is deprecated, that is, the use is allowed, but discouraged for some reason.

Syntax

[[deprecated]]	(1)
[[deprecated( string-literal )]]	(2)

string-literal

-

text that could be used to explain the rationale for deprecation and/or to suggest a replacing entity

Explanation

Indicates that the use of the name or entity declared with this attribute is allowed, but discouraged for some reason. Compilers typically issue warnings on such uses. The string-literal, if specified, is usually included in the warnings.

This attribute is allowed in declarations of the following names or entities:

• class/struct/union: struct [[deprecated]] S;,
• typedef-name, including those declared by alias declaration: [[deprecated]] typedef S* PS;, using PS [[deprecated]] = S*;,
• variable, including static data member: [[deprecated]] int x;,
• non-static data member: union U { [[deprecated]] int n; };,
• function: [[deprecated]] void f();,
• namespace: namespace [[deprecated]] NS { int x; }
• enumeration: enum [[deprecated]] E {};,
• enumerator: enum { A [[deprecated]], B [[deprecated]] = 42 };. (since C++17)
• template specialization: template<> struct [[deprecated]] X<int> {};

A name declared non-deprecated may be redeclared deprecated. A name declared deprecated cannot be un-deprecated by redeclaring it without this attribute.

Example

Run this code

#include <iostream>
 
[[deprecated]]
void TriassicPeriod() {
    std::clog << "Triassic Period: [251.9 - 208.5] million years ago.\n";
}
 
[[deprecated("Use NeogenePeriod() instead.")]]
void JurassicPeriod() {
    std::clog << "Jurassic Period: [201.3 - 152.1] million years ago.\n";
}
 
[[deprecated("Use calcSomethingDifferently(int).")]]    
int calcSomething(int x) {
    return x * 2;
}
 
int main()
{
    TriassicPeriod();
    JurassicPeriod();
}

Possible output:

Triassic Period: [251.9 - 208.5] million years ago.
Jurassic Period: [201.3 - 152.1] million years ago.
 
main.cpp:20:5: warning: 'TriassicPeriod' is deprecated [-Wdeprecated-declarations]
    TriassicPeriod();
    ^
main.cpp:3:3: note: 'TriassicPeriod' has been explicitly marked deprecated here
[[deprecated]]
  ^
main.cpp:21:5: warning: 'JurassicPeriod' is deprecated: Use NeogenePeriod() instead [-Wdeprecated-declarations]
    JurassicPeriod();
    ^
main.cpp:8:3: note: 'JurassicPeriod' has been explicitly marked deprecated here
[[deprecated("Use NeogenePeriod() instead")]]
  ^
2 warnings generated.