Performs compile-time assertion checking.
Syntax
static_assert ( bool_constexpr , message ) | (since C++11) | |
static_assert ( bool_constexpr ) | (since C++17) |
Explanation
| bool_constexpr | - | a constant expression that is contextually convertible to bool |
| message | - | optional (since C++17)string literal that will appear as compiler error if bool_constexpr is false |
A static assert declaration may appear at block scope (as a block declaration) and inside a class body (as a member declaration).
If bool_constexpr returns true, this declaration has no effect. Otherwise a compile-time error is issued, and the text of message, if any, is included in the diagnostic message.
Note
Since message has to be a string literal, it cannot contain dynamic information or even a constant expression that is not a string literal itself. In particular, it cannot contain the name of the template type argument.
Example
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 | #include <type_traits> template <class T>void swap(T& a, T& b){ static_assert(std::is_copy_constructible<T>::value, "Swap requires copying"); static_assert(std::is_nothrow_move_constructible<T>::value && std::is_nothrow_move_assignable<T>::value, "Swap may throw"); auto c = b; b = a; a = c;} template <class T>struct data_structure{ static_assert(std::is_default_constructible<T>::value, "Data Structure requires default-constructible elements");}; struct no_copy{ no_copy ( const no_copy& ) = delete; no_copy () = default;}; struct no_default{ no_default () = delete;}; int main(){ int a, b; swap(a, b); no_copy nc_a, nc_b; swap(nc_a, nc_b); // 1 data_structure<int> ds_ok; data_structure<no_default> ds_error; // 2} |
Possible output:
1 2 | 1: error: static assertion failed: Swap requires copying2: error: static assertion failed: Data Structure requires default-constructible elements |
See also
C documentation for static_assert |
Please login to continue.