I am trying to find the maximum of two strings and it is giving me the correct answer in the first case (when passing std::string variables) but giving an error in the second case (when passing direct strings).
#include<bits/stdc++.h>
using namespace std;
int main()
{
// Case 1
string str1 = "abc", str2 = "abcd";
cout << max(str1, str2) << endl;
// Case 2
cout << max("abc", "abcd") << endl;
}
In your second case,
std::cout << std::max("abc", "abcd") << std::endl;
they are string literals, in which "abc" has type char const [4] and "abcd" has type char const [5].
Therefore, in the function call std::max("abc", "abcd"), the std::max has to deduce
auto max(char const (&a)[4], char const (&b)[5]) {
return a < b ? b : a;
}
This is not possible as the std::max has no function template overload, which takes different types as template arguments. Hence, the error!
If you explicitly mention the template type const char* in std::max, this could have been compiled. This is because, for "abc" and "abcd" the type can be also be const char*s due to array to pointer decay in C++.
std::cout << std::max<const char*>("abc", "abcd" ) << '\n'; // compiles
^^^^^^^^^^^^^
In addition, the std::initializer_list overload of the std::max, in turn will deduce the above also const char* as template type:
std::cout << std::max({ "abc", "abcd" }) << '\n'; // compiles
However, you should not be doing it !
As @AlanBirtles pointed out, this can cause the undefined behavior, due to the fact that the std::max will compare the pointers of the two different arrays. The result can not be relayed and should be doing the above. Use the std::string for comparison as in your first case. Using string literals (since C++14), you can do a minimal change, and make the second case, same as first one:
#include <string>
using namespace std::string_literals;
std::cout << std::max("abc"s, "abcd"s) << '\n';
As a side note, see the followings: