# static assert declaration

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< c‎ | language

### Syntax

`_Static_assert` `(` expression `,` message `)` |  | (since C11)
`_Static_assert` `(` expression `)` |  | (since C2x)

expression | - | any integer constant expression
message | - | any string literal

This keyword is also available as convenience macro `static_assert`, available in the header `<assert.h>`.

### Explanation

The constant expression is evaluated at compile time and compared to zero. If it compares equal to zero, a compile-time error occurs and the compiler must display message (if provided) as part of the error message (except that characters not in basic source character set aren't required to be displayed).

Otherwise, if expression does not equal zero, nothing happens; no code is emitted.

### Keywords

`_Static_assert`

### Example

Run this code

    #include <assert.h>
    int main(void)
    {
        // Test if math works.
        static_assert(2 + 2 == 4, "Whoa dude!"); // or _Static_assert(...

        // This will produce an error at compile time.
        static_assert(sizeof(int) < sizeof(char),
                     "this program requires that int is less than char");
    }

### References

- C11 standard (ISO/IEC 9899:2011):

  - 6.7.10 Static assertions (p: 145)

  - 7.2 Diagnostics <assert.h> (p: 186-187)

### See also

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