Static Assertion

 

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Performs compile-time assertion checking

Syntax

static_assert ( bool_constexpr , string )		(since C++11)

Explanation

• bool_constexpr a boolean constant expression to be evaluated
• string string literal that will appear as compiler error if bool_constexpr is false

Example

#include <type_traits>
 
template<class T>
    void swap( T& a, T& b)
    {
        static_assert(std::is_copy_constructible<T>::value,
                      "Swap requires copying");
 
        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

See also

• assert
• type traits