Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Bugs in Hello World

blog.sunfishcode.online

Post reply on HN
Print view View original

71–80 of 262 posts

Re: Bugs in Hello World

#71

Post by usrbinbash »

mccorrinall wrote: post #13

Imo this is because the responsibility is not clearly defined and can be argued upon. If my program writes to the standard output, but you choose to redirect the pipe to a different location, is it my program’s responsibility to check what happens to the bytes AFTER the pipe? After all: my program did output everything as expected . The part which fucked up was not part of my program. I can see why some projects deci…

> but you choose to redirect the pipe to a different location

The output doesn't go into a pipe however, the output goes to /dev/full. Redirection happens before the process is started, so the program is, in fact, writing directly to a file descriptor that returns an error upon write.

Re: Bugs in Hello World

#72

Post by jwilk »

s_ariga wrote: post #49

#include #include int main(void) { if(puts("Hello, World!")!=EOF) { return EXIT_SUCCESS; }else { return EXIT_FAILURE; } }

This still succeeds, because puts() is buffered.

(And silently returning non-zero would be bad anyway.)

Re: Bugs in Hello World

#73

Post by pdw »

xlii wrote: post #32

I’m disappointed. I expected some obscure edgecase (like “Main is usually a function…” [1]) but instead that’s about scope handling, contract design and responsibility shift. “Hello world” method simply calls an API to a text interface. It uses simple call, to a simple interface that is expected to be ever present. I don’t find any bug there. It won’t work if such interface isn’t available, is blocked or doesn’t exis…

I found it interesting. If you generalize a bit, the question is "Will a naively written stdio program handle IO errors?". The fact that for several popular languages the answer is "no" is disappointing.

Re: Bugs in Hello World

#74

Post by Karellen »

s_ariga wrote: post #49

#include #include int main(void) { if(puts("Hello, World!")!=EOF) { return EXIT_SUCCESS; }else { return EXIT_FAILURE; } }

puts(), like printf() and all the C-standardised "stdio" functions use buffered writes. So that is also buggy, because the buffer won't be flushed until after main() returns. You need to call and check the return value of "fflush(stdout)" manually to get the correct result.

Re: Bugs in Hello World

#76

Post by jll29 »

onion2k wrote: post #20
bestouff wrote: post #2

Well that's precisely the mindset of C/C++. You have to think by yourself about everything that can go wrong with your code. And, man, lots of things can go wrong. I find more modern languages so much less exhausting to use to write correct code.

I find more modern languages so much less exhausting to use to write correct code. Modern languages do catch more programmer errors than C/C++, but the more general point is that there are "edge cases" (redirecting to a file isn't an edge case) that developers need to consider that aren't magically caught, and understanding the language you use well enough so as not to write those bugs is important. The more experien…

Exactly. And isn't UNIX all about writing tools that can be used in unintended ways and combinations?

Re: Bugs in Hello World

#77

Post by jwilk »

enriquto wrote: post #21

Ignoring the return of printf is a "bug". For the hello-world example, you can simply pass the printf value to main: "return printf(...) > 0;"

That's insufficient, because printf() is buffered.

Re: Bugs in Hello World

#78

Post by PennRobotics »

s_ariga wrote: post #49

#include #include int main(void) { if(puts("Hello, World!")!=EOF) { return EXIT_SUCCESS; }else { return EXIT_FAILURE; } }

puts() returns 13 with no pipe and with pipe to /dev/full, which I just learned is due to buffering.

What worked for me initially was the POSIX write() function:

  #include 
  #include 
  
  int main(void)
  {
      int status;
      status = write(1, "Hello World!\n", 13);
      if (status
-----

As someone else commented, fflush() gives the desired error response.

  #include 
  #include 
  
  int main(void)
  {
      int status;
      puts("Hello World!");
      status = fflush(stdout);
      if (status
-----

andreyv probably has the best alternative[1], which is checking fflush() and ferror() at the program's end and calling perror(). It's better because it outputs an actual error message on the current terminal, and you don't need to write a special error checking wrapper.

[1] https://news.ycombinator.com/item?id=30611924

Re: Bugs in Hello World

#79

Post by jll29 »

sunfish wrote: post #22
Reventlov wrote: post #5

And to catch such a thing in C, if anyone was wondering, you would have to fflush stdout.

This is true, however if we modify the program to print a 4096-byte long string instead of just the "hello world" string, then it's not sufficient again. And of course, the number 4096 is system-dependent. So to really do hello world in C right, in addition to fflush, you also need to check the return value from puts. I've never seen any C tutorial do that though.

#include

int main(void) { return !(puts("Hello, new world!") == EOF); /* return 0 unless a rare I/O error occurs */ }

Post reply on HN