CODEWITHSUNDEEP
c++string
Nikos Athanasiou
Nikos Athanasiou

Reputation: 31549

std::string comparison, lexicographical or not

The following code, comes from the article C++ quirks, part 198276

include <iostream>
#include <string>

using namespace std;

int main() 
{
    std::string a = "\x7f";
    std::string b = "\x80";
    cout << (a < b) << endl;
    cout << (a[0] < b[0]) << endl;

    return 0;
}

Surprisingly the output is 

1
0

Shouldn't string comparison be lexicographical ? If yes how is the output explained?

Upvotes: 3

Views: 655

Answers (2)

Bill Lynch
Bill Lynch

Reputation: 81976

So I'm just going to quote directly from your link:

It turns out that this behavior is required by the standard, in section 21.2.3.1 [char.traits.specializations.char]: “The two-argument members eq and lt shall be defined identically to the built-in operators == and < for type unsigned char .”

So:

  • (a < b) is required to use unsigned char comparisons.
  • (a[0] < b[0]) is required to use char comparisons, which may or may not be signed.

Upvotes: 2

Some programmer dude
Some programmer dude

Reputation: 409356

There is nothing in the C++ specification to say if char is signed or unsigned, it's up to the compiler. For your compiler it seems that char defaults to signed char which is why the second comparison returns false.

Upvotes: 3

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