Struct Variable Query

Question

#include<bits/stdc++.h>
using namespace std;
typedef struct trie
{
    int arr[26];
    bool isleaf;
    trie(int isleaf)
    {
        this->isleaf=9;
        cout<<isleaf<<endl;
        isleaf=false;
        cout<<isleaf<<endl;
        cout<<this->isleaf<<endl;
    }
}* tr;
//void inser(s)
int main()
{
   tr k=new trie(3);
   cout<<k->isleaf;
}

Works Fine and outputs

But in

#include<bits/stdc++.h>
using namespace std;
typedef struct trie
{
    int arr[26];
    bool isleaf;
    trie(int isleaf)
    {
        cout<<isleaf<<endl;
        isleaf=false;
        cout<<isleaf<<endl;
        cout<<this->isleaf<<endl;
    }
}* tr;
//void inser(s)
int main()
{
   tr k=new trie(3);
   cout<<k->isleaf;
}

I get

I understand that it is uninitialized but still why 68?

If use a normal bool either in global or inside function and print it without initializing i get 0,then why not here?

And can somebody also point out some good source to clear doubts about such variable declarations , public and private concepts , and OOPS, difference between structs and classes etc.

Asking for the behavior of undefined behavior is mostly futile. — πάντα ῥεῖ, Jun 29 '17 at 13:17
the thing is i am not asking about what value gets assigned to it. why a bool gives a 68 when it is supposed to be if 1 bit — Rohan Aggarwal, Jun 29 '17 at 13:18
Because that's what was there when the program loaded? Because the compiler you use always initializes ints to 68? Because that's your lucky number? — kabanus, Jun 29 '17 at 13:18
In case of global variables they are automatically initialized with default values. — GAURANG VYAS, Jun 29 '17 at 13:19
@RohanAggarwal _"when it is supposed to be if 1 bit"_ There's no such thing like a _single bit variable_. — πάντα ῥεῖ, Jun 29 '17 at 13:20
no no i know that we work in bytes. but shouldn't the cout print according considering bool can be only 0 or 1 — Rohan Aggarwal, Jun 29 '17 at 13:21
because the value stored there before in the memory wasn't interpreted as bool expression — W.F., Jun 29 '17 at 13:26
ok @W.F. that seems logical so until i initialize it , it will never be treated as a bool — Rohan Aggarwal, Jun 29 '17 at 13:28
@RohanAggarwal Also read [Why should I not #include ?](https://stackoverflow.com/questions/31816095/why-should-i-not-include-bits-stdc-h) please. — πάντα ῥεῖ, Jun 29 '17 at 13:31
Try this code on other OS/compilers. You will find many will output 0. It's very dependent on where/how you compile and run. — kabanus, Jun 29 '17 at 13:34
@gaurangvyas no i was not confused in that , just because when it was not initialized i wanted it to still give 0 or 1 , i was surprised on 68 now it got cleared — Rohan Aggarwal, Jun 29 '17 at 13:44

score 0 · Answer 1 · answered Jun 29 '17 at 14:45

[basic.fundamental]/6 Values of type bool are either true or false.⁴⁹

Footnote 49) Using a bool value in ways described by this International Standard as “undefined,” such as by examining the value of an uninitialized automatic object, might cause it to behave as if it is neither true nor false.

Undefined behavior is undefined. That's the long and the short of it. It's really pointless to discuss why a program exhibiting undefined behavior happens to manifest it in a particular way.

Struct Variable Query

1 Answers1