C attribute: deprecated (since C23)
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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 ]][[ __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 |
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.
Example
Run this code
#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.