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

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Attributes
deprecated
(C++14)
(C++17)
(C++20)(C++20)
(C++23)
 

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

Contents

[edit] Syntax

[[deprecated]] (1)
[[deprecated( string-literal )]] (2)
string-literal - an unevaluated string literal that could be used to explain the rationale for deprecation and/or to suggest a replacing entity

[edit] 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:

  • [[deprecated]] typedef S* PS;,
  • using PS [[deprecated]] = S*;,
  • (non-member) variable, e.g., [[deprecated]] int x;,
  • static data member, e.g., struct S { [[deprecated]] static constexpr char CR{13}; };,
  • non-static data member, e.g., union U { [[deprecated]] int n; };,
  • function, e.g., [[deprecated]] void f();,
  • namespace, e.g., namespace [[deprecated]] NS { int x; },
  • enumeration, e.g., enum [[deprecated]] E {};,
  • enumerator, e.g., enum { A [[deprecated]], B [[deprecated]] = 42 };,
(since C++17)

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

[edit] Example

#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.

[edit] See also

C documentation for deprecated