i want to know at compile time if a template parameter is const char*, example :
static_assert(!is_pointer_to_const_char("test"));
will assert.
Thanks !
Hard-coded string in your example, is not "const char *", but array of "const char[N]". You need to handle this case especially:
template<typename T, std::size_t N>
constexpr bool is_pointer_to_const_char(T(&)[N])
{
return std::is_same_v<const char, T>;
}
template<typename T>
constexpr bool is_pointer_to_const_char(T &&)
{
return std::is_same_v<const char *, T>;
}
int main()
{
string s1 = "str";
static_assert(!is_pointer_to_const_char(123)); //NOT ASSERTED
static_assert(!is_pointer_to_const_char("123")); //ASSERTED!
static_assert(!is_pointer_to_const_char(s1.c_str())); //ASSERTED!
}
The std::is_same
does exactly what you ask:
std::cout << std::is_same<const char*, const char*>::value;
std::cout << std::is_same<const char*, const char>::value;
std::cout << std::is_same<const char*, char*>::value;
std::cout << std::is_same<const char*, const unsigned char*>::value;
std::cout << std::is_same<const char*, const signed char*>::value;
std::cout << std::is_same<const char*, const volatile char*>::value;
The output of this code fragment is 100000 .
There is one caveat with const signed char*
and const unsigned char*
: these types are not the same as const char*
. You decide if that is what you need.
Regarding the usage in template, here is a sample:
template<typename T>
struct C
{
static int isParametrizedWithConstCharPtr()
{
return std:: is_same<const char*, T>::value;
}
};
std::cout << C<const char*>::isParametrizedWithConstCharPtr(); // 1
std::cout << C<const char>::isParametrizedWithConstCharPtr(); // 0
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