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

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assume (C++23)
carries_dependency (C++11)(until C++26)
deprecated (C++14)
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likely (C++20)
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unlikely (C++20)

[edit]

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

[edit]Syntax


`[[deprecated]]`	(1)

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

string-literal

anunevaluated 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. Thestring-literal, if specified, is usually included in the warnings.

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

class/struct/union, e.g.,struct[[deprecated]] S;,
typedef-name, including those declared byalias declaration, e.g.,

[[deprecated]]typedef S* PS;,
using PS[[deprecated]]= S*;,

(non-member) variable, e.g.,[[deprecated]]int x;,
static data member, e.g.,struct S{[[deprecated]]staticconstexprchar 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)

template specialization, e.g.,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.

[edit]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.