The code below outputs 1 and 0 how ever i do not know why

Question

I understand that the code below is outputing the result of a boolean question but i do not understand why it outputs 1 and 0 instead of 1 and 1.

#include <iostream>
using namespace std;

int main() 
{
    string d = "abc", e = "abc";
    char a[] = "abc", b[] = "abc";
    cout << (d == e);
    cout << (a == b);

    return 0;
}
//outputs 10

i also tried outputing the value stored in variables a and b and got the same value for both

#include <iostream>
using namespace std;

int main() 
{
    string d = "abc", e = "abc";
    char a[] = "abc", b[] = "abc";
    cout << (d == e);
    cout << (a == b);
    cout << "\n" << a << "\n";
    cout << b;

    return 0;
}
// outputs 10
//abc
//abc

also https://stackoverflow.com/questions/52814457/why-do-only-some-compilers-use-the-same-address-for-identical-string-literals — Pascal Ganaye, Jul 26 '20 at 22:09

score 1 · Answer 1 · answered Jul 26 '20 at 21:58

1

In C, std::string has a special operator== that actually compares the strings. Contrary to what you might read, std::strings are not equivalent to char arrays. Char arrays are essentially treated as pointers, so == compares the memory addresses, which are different, so the program will output 0.

answered Jul 26 '20 at 21:58

Aplet123

33,825
1
29
55

1

There is no `std::string` in C. – Adrian Mole Jul 26 '20 at 22:01
2

Arrays *decay* to pointers. – Jul 26 '20 at 22:01
1

`Char arrays are essentially treated as pointers` This is highly misleading. – eerorika Jul 26 '20 at 22:03
You're talking about c++, not c – jjj Jul 26 '20 at 22:07
1

Arrays ARE just pointers to sequential data in the memory – jjj Jul 26 '20 at 22:10
@jjj I'd say there's a difference: https://godbolt.org/z/P1z74j Calling `foo2` in that example would not be possible with a pointer and arithmetics with that type yields a different result than with a plain pointer. – Ted Lyngmo Jul 26 '20 at 22:27

score 1 · Answer 2 · answered Jul 26 '20 at 22:04

1

For comparing 2 arrays of char you should use strcmp, the == operators compares the pointer addresses instead of the value itself. You can also iterate the arrays and compare element by element.

answered Jul 26 '20 at 22:04

Diana

140
5

The code below outputs 1 and 0 how ever i do not know why

2 Answers2