static assart

A static_assert is a feature in C++ that allows you to check a condition at
compile-time and produce a compile-time error if the condition is not true. It is 
defined in the <cassert> header and it is used to ensure that certain conditions 
are met before the program is compiled, such as ensuring that a template parameter
is a certain type or that a variable has a certain value.

Here is an example of how to use a static_assert:

Copy code
template<typename T>
void print_type()
{
    static_assert(std::is_fundamental<T>::value, "The type must be a fundamental type");
    std::cout << "The type is a fundamental type" << std::endl;
}
In this example, the function print_type is a template function that takes a
single template parameter T. The static_assert statement checks if the type T is 
a fundamental type by using the std::is_fundamental type trait. If the type is not
a fundamental type, the compiler will produce an error with the message "The type
must be a fundamental type".

In this way, the use of static_assert allows to validate the input parameter at
the compilation time, avoiding unexpected behaviours on runtime, increasing the
robustness and security of the code.

It's worth noting that static_assert is a C++11 feature, so it might not be 
available on all compilers and platforms.

simple full code
Sure, here's a simple example that demonstrates the use of static_assert:

Copy code
#include <iostream>
#include <type_traits>

template<typename T>
void print_type(T value)
{
    static_assert(std::is_fundamental<T>::value, "The type must be a fundamental type");
    std::cout << "The value passed is of fundamental type: " << value << std::endl;
}

int main()
{
    int x = 5;
    print_type(x);

    std::string s = "hello";
    // This will cause a compile error because std::string is not a fundamental type
    // print_type(s);

    return 0;
}
In this example, the function print_type is a template function that takes a 
single template parameter T and an instance of the same type value. The 
static_assert statement checks if the type T is a fundamental type by using 
the std::is_fundamental type trait. If the type is not a fundamental type, the
compiler will produce an error with the message "The type must be a fundamental 
type".

In the main function, we are passing an integer variable x to the function, the 
function will print the value of the variable and since the type of the variable
is int which is a fundamental type, the code will compile and run without any
issues.

If you try to pass a variable of non-fundamental type, like the string variable
s, the compiler will produce an error as the static_assert condition is not met.

In this way, the use of static_assert allows you to check the input parameter at 
the compilation time, avoiding unexpected behaviours on runtime, increasing the
robustness and security of the code.