Static Assertion
From cppreference.com
Performs compile-time assertion checking
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[edit] Syntax
static_assert ( bool_constexpr , message )
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(since C++11) | ||||||||
static_assert ( bool_constexpr )
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(since C++17) | ||||||||
[edit] 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.
[edit] 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.
[edit] Example
Run this code
#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: error: static assertion failed: Swap requires copying 2: error: static assertion failed: Data Structure requires default-constructible elements
[edit] See also
C documentation for static_assert
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