comparing "1" and "0"

Apologies if this seems like a silly q, but why do the statements
cout << ("0" < "1")
cout << ("1" < "0") both return true?
:confused:

Because you're comparing pointers (to strings) rather than strings.


Try with

Code:

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#include <string>
std::string zero = "0";
std::string one = "1";
cout << (zero < one);

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similarily

Code:

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        cout << (*"0" < *"1");
        cout << (*"1" < *"0");

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Quote:

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Originally Posted by MadCow257

similarily

Code:

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        cout << (*"0" < *"1");
        cout << (*"1" < *"0");

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Ah, but what about (*"10" < *"11") ?

Thankyou all for such quick replies! :)
I'm still unclear on exactly how my example was working though.. I'm guessing that I was comparing pointers to both strings and so whatever I have on the left of the operator, the value of that pointer will always be less than that of the right pointer because of the order im putting them in memory? is this right or just rubbish? :)

Quote:

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Originally Posted by rayman

Thankyou all for such quick replies! :)
I'm still unclear on exactly how my example was working though.. I'm guessing that I was comparing pointers to both strings and so whatever I have on the left of the operator, the value of that pointer will always be less than that of the right pointer because of the order im putting them in memory? is this right or just rubbish? :)

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You are correct in that you've compared the memory addresses of the strings.

Whether the left or right string gets put in memory at a lower-valued memory location depends on the compiler and its behavior is generally unpredictable.

Quote:

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I'm still unclear on exactly how my example was working though.

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Whenever a string literal is encounted in a program(i.e. something between double quotes), the program slaps a '\0' character on the end of the string literal, stores it in memory somewhere, and returns the address. So, the line:

cout << ("0" < "1")

becomes:

cout<<(address of str1 < address of str2);

I'm kind of confused too

What's different with this

(*"10" < *"11")

and this

(*"0" < *"1")

*"10";

<==>

const char* const c = "10";
*c;

<==>

const char* const c = "10";
c[0];

<==>

'1'

not 10

I think you mean '1', not 1.

Quote:

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I'm kind of confused too

What's different with this

(*"10" < *"11")

and this

(*"0" < *"1")

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Magos??? How about this:

Code:

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const char* ptr1 = "123456789";
const char* ptr2 = "1";

cout<<*ptr1<<endl;  //'1'
cout<<*ptr2<<endl;  //'1'

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Quote:

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Originally Posted by rayman

Apologies if this seems like a silly q, but why do the statements
cout << ("0" < "1")
cout << ("1" < "0") both return true?
:confused:

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If that really happens with your compiler then I think it has to do that your compiler doesn't optimize string literals. It propably creates a char array for every literal in you program and doesn't check for duplicates.
g++ does

Code:

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# include <iostream>
# include <iomanip>

using namespace std;

int main() {
    cout << boolalpha;
    cout << "1 < 0 = " << ( "1" < "0" ) << endl;
    cout << "0 < 1 = " << ( "0" < "1" ) << endl;
    return 0;
}

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my output

Code:

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1 < 0 = true
0 < 1 = false

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As far as I know this is implementation defined behavour.
Kurt

Quote:

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As far as I know this is implementation defined behavour.

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It is. Compilers are free to store string literals anywhere, in any order.

If you want to compare string literals properly, use strcmp() or strings:

Code:

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if(strcmp("0", "1") < 0) { /* 0 is < 1 */ }
string one = "1", two = "2";
if(one < two) { /* 1 is < 2 */ }
if(string("11") < string("7")) { /* 11 is < 7 */ }

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