# 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.

### See also

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