Can someone explain, why the output is "C" in this code?
#include <iostream> using namespace std; template<class X> X maximum(X a,X b) { if(a > b) return a; else return b; } int main() { cout << maximum("C","D") << endl; } 
- lexicographical comparison is happening here.Build Succeeded– Build Succeeded2020-10-17 08:21:23 +00:00Commented Oct 17, 2020 at 8:21
- 2@BuildSucceeded no, it's not. It's just comparing 2 unrelated pointersAykhan Hagverdili– Aykhan Hagverdili2020-10-17 08:53:35 +00:00Commented Oct 17, 2020 at 8:53
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3 Answers
Note that in your case the type X will be inferred as const char*, hence you are comparing two const char *s i.e. the addresses of the two string literals.
If you want to get the expected result, use something like the following
cout << maximum("C"sv, "D"sv) << endl; // or cout << maximum<string_view>("C", "D") << endl; This compares two std::string_views, which is a lexicographical comparison, not a pointer comparison.
See std::string_view comparison operators, and see demo at Compiler Explorer.
Alternatively, use characters instead of using string literals i.e 'C' and 'D'. In that case, X will be deduced to char.
See also Why is "using namespace std;" considered bad practice?
Comments
When you use maximum("C","D"), the template parameter is char const*. You end up comparing two pointers. There is no guarantee which pointer will be greater. You have indeterminate behavior.
If you want to compare the string "C" and string "D", you can use:
cout << maximum(std::string("C"), std::string("D")) << endl; // or cout << maximum("C"s, "D"s) << endl; // or cout << maximum<std::string>("C", "D"); If you want compare just the characters C and D, you should use
cout << maximum('C', 'D') << endl; 4 Comments
Łukasz Ślusarczyk
or 'C' and 'D' if author wanted to compare just chars
R Sahu
@ŁukaszŚlusarczyk, indeed.
Remy Lebeau
For comparing string literals, consider using
maximum<std::string>(“C”, “D”), or maximum(“C”s, “D”s) like in asmmo’s answer.
M.M
*unspecified behaviour
If you want this to work for cstring-literals also, add overloads.
#include <cstring> template<class X> X maximum(X a, X b) { return a > b ? a : b; } char const* maximum(char const* a, char const* b) { return std::strcmp(a, b) > 0 ? a : b; } char* maximum(char* a, char* b) { return std::strcmp(a, b) > 0 ? a : b; } 