Hi there, anyone knows what's the most effective way to check undefined behavior?

All life is undefined behavior

All life is undefined behavior

`int *testint() { int a = 99; int *b = &a; return b; } int main() { int *a = testint(); std::cout << *a << std::endl; }` This code gives UB right?

i've tested with -fsanitize=undefined , it prints 1

`int *testint() { int a = 99; int *b = &a; return b; } int main() { int *a = testint(); std::cout << *a << std::endl; }` This code gives UB right?

Its ub

without giving any error

i used g++

and with also -Wall -Werror -pedantic-errors

without giving any error

IT's normal behaviour, but code with undefined behavior, 100%

and with also -Wall -Werror -pedantic-errors

and -Wextra

@suisei_v it print 99 normally, with fsanitize=undefined, it prints 1

`int *testint() { int a = 99; int *b = &a; return b; } int main() { int *a = testint(); std::cout << *a << std::endl; }` This code gives UB right?

It's not UB, you just return some address. However it's auto-freed by program when you returns from func, so you can't get value 99 by deref

Sometimes you get 99, sometimes not. It's random

From this point it's UB

Yes, but if i changed the code little bit to ` int *testint() { int a = 99; return &a; } `

i'll get address of stack memory associated with local variable 'a'

Compiler saves you from self-shooting

technically, they aren't different, why on the first code, compiler can't point that error out?

Because you use another variable to store address, so compiler thinks you know what are you doing

since both return pointer to the deallocated memory address

oh, ok

You can write int *foo() { int *b = 84230482; return (b); }

Compiler will say nothing

I'm not sure, but modern compilers should warn you.

Lemme check.

You just return a value. UB is about dereference it. But when you try to return address of local var, compiler will warn you

Interesting.

GCC does warn you, just not how I expected.

test.c: In function ‘foo’: test.c:2:11: warning: initialization makes pointer from integer without a cast [-Wint-conversion] int *b = 84230482;

so yeah, it doesn't.

It's about casting, not returning

yes.

One has to be wary of pointers.

True

83. Program to find area of triangle using Heron's formula. #include<stdio.h> #include<conio.h> #include<math.h> void main() { double a, b, c, s, area; clrscr(); printf("\nEnter the sides of triangle : \n"); scanf("%lf%lf%lf", &a, &b, &c); s = (a + b + c) / 2; area = sqrt(s * (s - a) * (s - b) * (s - c)); printf("\nArea of triangle using Heron's Formula : %.2lf", area); getch(); }

Guys want to know

Meaning of lf

yes?

And double used

Meaning of lf

In printf scanf

GCC does warn you, just not how I expected.

i'm using gcc on mac

c++/4.2.1 Apple LLVM version 10.0.1 (clang-1001.0.46.4)

lf = let printf know you send double

https://en.wikipedia.org/wiki/Printf_format_string

technically lf = f, but a long time ago f means float lf means double

lf = let printf know you send double

If i use int input and output gets 0 why

so now lf = f

Oh

If i use int input and output gets 0 why

?

c++/4.2.1 Apple LLVM version 10.0.1 (clang-1001.0.46.4)

clang isn't gcc

But it should return a similar error

Clang-8 on Ubuntu throws this error for me.

test.c:2:7: warning: incompatible integer to pointer conversion initializing 'int *' with an expression of type 'int' [-Wint-conversion] int *b = 84230482; ^ ~~~~~~~~ 1 warning generated.

Anyways.

Pls how can one check if a directory is empty or not

If i use int input and output gets 0 why

Youmean you want to write %d in scanf or what

Pls how can one check if a directory is empty or not

What language and what OS?

Pls how can one check if a directory is empty or not

google it with your os

If i use float instead of double and f instead of lf answer is same but if i use int it shows 0 input as well as output

use int where? You use %d in the format string?

But it should return a similar error

C++ on your PC does return the error?

C++ on your PC does return the error?

Both Clang-8 and g++-7 do return a warning, yes.

from my first code? do you use any particular flag ?

Oh, not your code.

If i use float instead of double and f instead of lf answer is same but if i use int it shows 0 input as well as output

ints and doubles stores differently in memory. If you just write int to double without cast the value wil not be accessible until correct casting

The code Vladimir sent.

Sorry to have misunderstood you.

@Remavas i've tested with multiple online compiler, there is no warning too

Don't mine me, I misunderstood you.

I was talking about Vladimir's code.

What's wrong with my msg

Any video lectures on c++

There are some lectures by Bjarne Stroustrup himself.

Any video lectures on c++

Youtube, Google?

Any video lectures on c++

For Indians, watch saurabh shukla videos.

For Indians, watch saurabh shukla videos.

Thanks

Pc game?

https://botondballo.wordpress.com/2019/07/26/trip-report-c-standards-meeting-in-cologne-july-2019/#lfts

Ok

/great

/get findprojects