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C attribute: deprecated (since C23)

From cppreference.com
< c‎ | language‎ | attributes

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 ]]
[[ __deprecated__ ]]
(1)
[[ deprecated ( string-literal ) ]]
[[ __deprecated__ ( string-literal ) ]]
(2)
string-literal - text 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:

  • struct/union: struct [[deprecated]] S;,
  • typedef-name: [[deprecated]] typedef S* PS;,
  • objects: [[deprecated]] int x;,
  • struct/union member: union U { [[deprecated]] int n; };,
  • function: [[deprecated]] void f(void);,
  • enumeration: enum [[deprecated]] E {};,
  • enumerator: enum { A [[deprecated]], B [[deprecated]] = 42 };.

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 <stdio.h>
 
[[deprecated]]
void TriassicPeriod(void)
{
    puts("Triassic Period: [251.9 - 208.5] million years ago.");
}
 
[[deprecated("Use NeogenePeriod() instead.")]]
void JurassicPeriod(void)
{
    puts("Jurassic Period: [201.3 - 152.1] million years ago.");
}
 
[[deprecated("Use calcSomethingDifferently(int).")]]
int calcSomething(int x)
{
    return x * 2;
}
 
int main(void)
{
    TriassicPeriod();
    JurassicPeriod();
}

Possible output:

Triassic Period: [251.9 - 208.5] million years ago.
Jurassic Period: [201.3 - 152.1] million years ago.
 
prog.c:23:5: warning: 'TriassicPeriod' is deprecated [-Wdeprecated-declarations]
    TriassicPeriod();
    ^
prog.c:3:3: note: 'TriassicPeriod' has been explicitly marked deprecated here
[[deprecated]]
  ^
prog.c:24:5: warning: 'JurassicPeriod' is deprecated: Use NeogenePeriod() instead. [-Wdeprecated-declarations]
    JurassicPeriod();
    ^
prog.c:9:3: note: 'JurassicPeriod' has been explicitly marked deprecated here
[[deprecated("Use NeogenePeriod() instead.")]]
  ^
2 warnings generated.

[edit] See also

C++ documentation for deprecated