I am trying to create a very simple function:
bool is_palidrome(const std::string& s)
{
std::string r(s.crbegin(), s.crend());
return s==r;
}
In order to avoid unnecessary allocations I thought I could use a string_view:
bool is_palidrome(const std::string& s)
{
std::string_view r(s.crbegin(), s.crend());
return s==r;
}
However the last function fails to compile since the compiler cannot find a suitable constructor (I tried both g++ 12.2 and clang++ 15.0). Why there isn't a constructor for this case while std::string_view r(s.cbegin(), s.cend());
works perfectly? I check the standard https://en.cppreference.com/w/cpp/string/basic_string_view/basic_string_view but I do not see which condition is not satisfied.
You don't need std::string_view
to do this.
To implement your approach - comparing the entire string with its reverse - you can use std::equal
.
bool is_palindrome(const std::string& s)
{
return std::equal( begin(s), end(s), rbegin(s) );
}
First it is better to have argument as std::string_view
(so literals and std::string are covered without any extra allocations).
Then you need to check only half of the range and use algoritm std::equal
(as in other answer).
bool is_palidrome(std::string_view s)
{
return std::equal(begin(s), begin(s) + size(s) / 2, rbegin(s));
}
Note ADL allows to skip some std::
.
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