Why compare operator <,>,= given wrong output when comparing strings?

Question

I am comparing two string using comparison operators(<,>,=).

The output of "a" < "b" In this case is 0.

#include<iostream>
using namespace std;
int main()
{
    cout<<("a" < "a")<<endl;
    cout<<("b" < "a")<<endl;
    cout<<("a" < "b")<<endl;

    return 0;
}

outputs -

0
1
0

But why the output is changing when i am comparing only "a" < "b" ?

#include<iostream>
using namespace std;
int main()
{
    // cout<<("a" < "a")<<endl;
    // cout<<("b" < "a")<<endl;
    cout<<("a" < "b")<<endl;

    return 0;
}

output - 1

Here are the SS-

[1st output]https://i.stack.imgur.com/rHqzM.png

[2nd output]https://i.stack.imgur.com/IrUEx.png

I have so confused right now !! pls anyone can assist me with this

you are not comparing strings, you are comparing arrays which decay to pointers — 463035818_is_not_an_ai, Jun 20 '23 at 12:03
strings in c++ are `std::string`. `std::string("a") < std::string("b")` you want — 463035818_is_not_an_ai, Jun 20 '23 at 12:03
do not ignore compiler warnings ! https://godbolt.org/z/qjWx6Mx84 ! — 463035818_is_not_an_ai, Jun 20 '23 at 12:05
@463035818_is_not_an_ai C-style strings remain part of C++. In fact arguably more so than `std::string` which is part of the library, while support for literal string constants as in this example is _built-in_. — Clifford, Jun 20 '23 at 12:18
In an expression a literal string constant has type `const char*` - you are comparing pointers, not strings. C-style strings are not data types. Use `std::strcmp()` or the `std::string` class for which these operators have overloads. — Clifford, Jun 20 '23 at 12:22
`"a" < "b"` compares the address of the first character in both string literals. Since the layout of string literals in memory is unspecified, there is no guarantee of what the comparison will produce. If you want to do lexicographic comparison (which will compare characters in the string individually) either use `std::strcmp("a", "b")` (which produces a negative value for "less than", zero for equal, and a positive value for "greater than") or use `std::string` (e.g. `std::string("a") < std::string("b")`) or (since C++11) `std::string` literals (e.g. `"a"s < "b"s`). — Peter, Jun 20 '23 at 12:59

bitmask · Answer 1 · 2023-06-20T12:17:53.553

2

You are not comparing std::string objects with well defined inequality operations. You are comparing string literals with unspecified memory locations. Therefore < will not return what you expect:

The type of an unprefixed string literal is const char[N], where N is the size of the string [..], including the null terminator.

edited Jun 20 '23 at 12:17

answered Jun 20 '23 at 12:03

bitmask

32,434
14
99
159

Ah ... the meaning of comparing string literals has well-defined inequality operations. It is comparing the address of the first character of each (statically allocated) string literal. The *result* of the comparison is unspecified (since the layout in memory is unspecified). – Peter Jun 20 '23 at 13:02
@Peter Yep, as I say, the memory location is unspecified. Therefore the result is not what OP was expecting. – bitmask Jun 20 '23 at 13:15

Why compare operator <,>,= given wrong output when comparing strings?

1 Answers1