C/C++ Programming Questions Not Worth Their Own Thread

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That Turkey Story: Mar 30, 2003

Ugg boots posted:

We talked a couple of days ago, you mentioned that you lost your job and seemed pretty bummed about it. Nothing a week of video games won't fix though, right?

Edit: Or you could spend your time in COBOL and make some origami versions of peoples' avatars!

Whoever you are you're gay as hell!

# ? Apr 4, 2009 20:35

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# ? Apr 29, 2024 18:16

Avenging Dentist: Oct 1, 2005; oh my god is that a circular saw that does not go in my mouth aaaaagh

If it helps, they're (probably) going to extend the lower-price early registration fee for Boostcon until a week before it starts.

# ? Apr 4, 2009 20:39

Contero: Mar 28, 2004

What is the simple, clean way to read in either a float or int from stdin in C?

>5 oh an int! (5) >5.3 a float! (5.3) >blah not a float or int!

code:

void readit(void)
{
   int i;
   float f;

   //...
   if (...)
      printf("oh an int! (%d)\n", i);
   else if (...)
      printf("a float! (%f)\n", f);
   else
      printf("not a float or int!\n");
}

Because the only solutions I can think of are pretty gross/hackish.

# ? Apr 6, 2009 04:10

Avenging Dentist: Oct 1, 2005; oh my god is that a circular saw that does not go in my mouth aaaaagh

You're going to have to be a lot more specific. Is 1.23E2 a float or an int?

# ? Apr 6, 2009 04:13

Contero: Mar 28, 2004

#.#[E#] / nan / inf is a float
# is an int
anything else falls through.

# ? Apr 6, 2009 04:17

Zakalwe

May 12, 2002

Wanted For:

Terrorism
Kidnapping
Poor Taste
Unlawful Carnal Gopher Knowledge

Probably an overcomplicated and long-winded method but...

Read a string. Check for a decimal point, E etc.

Use boost::lexical_cast to get the string into the required format. (int or float)

# ? Apr 6, 2009 04:37

Avenging Dentist: Oct 1, 2005; oh my god is that a circular saw that does not go in my mouth aaaaagh

Zakalwe posted:

Use boost::lexical_cast to get the string into the required format. (int or float)

Contero posted:

in C?

(P.S. http://codepad.org/l9GkajTc)

# ? Apr 6, 2009 05:09

Null Pointer: May 20, 2004; Oh no!

Zakalwe posted:

Probably an overcomplicated and long-winded method but...

Avenging Dentist posted:

Or meet somewhere in the middle: search the string for a decimal or an E, and then use sscanf's return value to determine valid input. :colbert:

# ? Apr 6, 2009 05:22

Vanadium: Jan 8, 2005

I tried to come up with a way to use scanf's return value for this but I am seriously at a loss there. And I did not even think of strtol.

# ? Apr 6, 2009 05:27

Null Pointer: May 20, 2004; Oh no!

Vanadium posted:

I tried to come up with a way to use scanf's return value for this but I am seriously at a loss there. And I did not even think of strtol.

scanf requires you to specify the input's type in the format string. There is no way to use scanf to detect the type of the input, only whether or not an input is matched.

# ? Apr 6, 2009 05:40

Vanadium: Jan 8, 2005

Yeah, the plan was kind of to try reading it as both integer and floating-point type, but since scanf only returns the amount of items matched and not the amount of bytes consumed, that was not of any use at all. welp.

# ? Apr 6, 2009 05:44

Contero: Mar 28, 2004

Avenging Dentist posted:

(P.S. http://codepad.org/l9GkajTc)

strtol we meet again!

(thanks)

# ? Apr 6, 2009 06:57

Lexical Unit: Sep 16, 2003

I had pretty much the exact same code AD posted but whenever I tried to print out the value of the double it would come out as garbage. Finally, including stdlib.h fixed the issue. I'm not very versed in straight C, what's the reason for this?

Fake edit: I should have turned on all warnings.

gcc posted:

warning: implicit declaration of function �strtol� warning: implicit declaration of function �strtod�

How is this only a warning, and not an error?

# ? Apr 6, 2009 17:36

Blotto Skorzany: Nov 7, 2008; He's a PSoC, loose and runnin'
came the whisper from each lip
And he's here to do some business with
the bad ADC on his chip
bad ADC on his chiiiiip

Lexical Unit posted:

How is this only a warning, and not an error?

Builtins are the excuse iirc

# ? Apr 6, 2009 17:37

rjmccall: Sep 7, 2007; no worries friend; Fun Shoe

Lexical Unit posted:

I had pretty much the exact same code AD posted but whenever I tried to print out the value of the double it would come out as garbage. Finally, including stdlib.h fixed the issue. I'm not very versed in straight C, what's the reason for this?

C specifies what happens when you call a function with no declaration; essentially, it's as if you were calling a function declared int (*)(...). Now, first off, doubles generally get returned in totally different registers from ints, but even if they didn't, the logical operation here as far as C is concerned is to take an int value from somewhere (in this case, probably trash) and transform it to a double.

Lexical Unit posted:

Fake edit: I should have turned on all warnings.
How is this only a warning, and not an error?

Foolishness.

# ? Apr 6, 2009 17:46

Mustach: Mar 2, 2003; In this long line, there's been some real strange genes. You've got 'em all, with some extras thrown in.

rjmccall posted:

Foolishness.

Yes, so foolish that it was made an error in C99.

# ? Apr 6, 2009 17:52

Contero: Mar 28, 2004

Mustach posted:

Yes, so foolish that it was made an error in C99.

$ gcc -std=c99 -Wall -o bla test.c test.c: In function �main�: test.c:17: warning: implicit declaration of function �strtol� test.c:19: warning: implicit declaration of function �strtod�

code:

#include <errno.h>
#include <stdio.h>
//#include <stdlib.h>
#include <string.h>

int main ()
{
   int i;
   double f;
   char buffer[256];
   char *end;
   char *out;

   while(EOF != fscanf(stdin, " %s", buffer)) {
      end = buffer + strlen(buffer);
      errno = 0;
      if ( ((i = strtol(buffer, &out, 10)) || errno == 0) && out == end)
         printf("long: %d\n", i);
      else if ( ((f = strtod(buffer, &out)) || errno == 0) && out == end)
         printf("double: %lf\n", f);
      else
         printf("whatever: %s\n", buffer);
   }
   
   return 0;
}

# ? Apr 6, 2009 21:03

Vanadium: Jan 8, 2005

$ gcc -x c++ -o test{,.c} test.c: In function �int main()�: test.c:17: error: �strtol� was not declared in this scope test.c:19: error: �strtod� was not declared in this scope

:smug:

# ? Apr 6, 2009 21:05

Blotto Skorzany: Nov 7, 2008; He's a PSoC, loose and runnin'
came the whisper from each lip
And he's here to do some business with
the bad ADC on his chip
bad ADC on his chiiiiip

gcc is not a stardards-conforming compiler by any stretch of the imagination, Contrero

Also try it with -std=c99 -pedantic

# ? Apr 6, 2009 21:08

Mustach: Mar 2, 2003; In this long line, there's been some real strange genes. You've got 'em all, with some extras thrown in.

Contero posted:

http://gcc.gnu.org/c99status.html posted:

remove implicit function declaration - Done

Don't ask me. Anyhow, it says so in paragraph 5 of the standard's Foreward.

# ? Apr 6, 2009 21:53

Cosmopolitan: Apr 20, 2007; Rard sele this wai -->

I'm working on UVa Problem 103 right now, and I need a little help. I've got everything working except the function which finds out which boxes fit into each other. The problem is with the solution I came up with, the UVa Judge tells me "Wrong Answer." I think part of my problem is that I'm just coming up with unnecessarily complex solutions.

This is an outline of the logic I came up with. This function is being sent a box which is sorted according to the sum of their elements:

Click here for the full 1260x297 image.

Could someone pitch me a simpler idea, or tell me what's wrong with mine?

Cosmopolitan fucked around with this message at 01:00 on Apr 7, 2009

# ? Apr 7, 2009 00:19

shrughes: Oct 11, 2008; (call/cc call/cc)

Anunnaki posted:

Could someone pitch me a simpler idea, or tell me what's wrong with mine?

That you're trying to express it with a flowchart. Why don't you explain your idea with something more readable, like actual code?

Edit: Heck, even pseudocode!

# ? Apr 7, 2009 02:51

floWenoL: Oct 23, 2002

Anunnaki posted:

Could someone pitch me a simpler idea, or tell me what's wrong with mine?

Wow flowcharts really *are* useless for anything except the most trivial of algorithms. If you rewrite it as pseudocode I'm sure it'll be easier to see if you did anything wrong.

# ? Apr 7, 2009 02:51

Contero: Mar 28, 2004

Mustach posted:

Don't ask me. Anyhow, it says so in paragraph 5 of the standard's Foreward.

I was sincerely confused, not being a jackass. It's hard to tell the difference in CoC I guess.

# ? Apr 7, 2009 03:07

Mr.Radar: Nov 5, 2005; You guys aren't going to believe this, but that guy is our games teacher.

Does anyone have any suggestions for good books or tutorials on test driven development and unit testing with C++? I'm starting a new project and I'd like to give TDD a try. Google's top results look pretty good, but some of that material is out of date and isn't very in-depth and there's a lot of .Net results in there.

Mr.Radar fucked around with this message at 03:27 on Apr 7, 2009

# ? Apr 7, 2009 03:09

narfanator: Dec 16, 2008

I found the Boost TDD tutorial thing really helpful in general, you might take a look.

# ? Apr 7, 2009 05:17

Mustach: Mar 2, 2003; In this long line, there's been some real strange genes. You've got 'em all, with some extras thrown in.

Contero posted:

I was sincerely confused, not being a jackass. It's hard to tell the difference in CoC I guess.

Oh no, I didn't think you were a jackass. Sorry if I seemed that way.

# ? Apr 7, 2009 15:41

newsomnuke: Feb 25, 2007

code:

class Foo
{
	friend std::ostream& operator << (std::ostream& os, const Foo& a_var);

	int m_type;
	union
	{
		int m_int;
		float m_float;
	};
	
	// Member functions
	// ...
};

Why does sizeof(Foo) give me 12? Is there some odd padding going on, or is there something in the member functions which might be taking up space?

# ? Apr 7, 2009 17:31

rjmccall: Sep 7, 2007; no worries friend; Fun Shoe

ultra-inquisitor posted:

Why does sizeof(Foo) give me 12? Is there some odd padding going on, or is there something in the member functions which might be taking up space?

If any of them are virtual, or if you have a virtual base class (which I mention only for completion, since you obviously don't), yes. Other than that, what platform are you compiling on?

# ? Apr 7, 2009 17:41

ShoulderDaemon: Oct 9, 2003; support goon fund; Taco Defender

ultra-inquisitor posted:

Why does sizeof(Foo) give me 12? Is there some odd padding going on, or is there something in the member functions which might be taking up space?

Virtual members take up space because a function pointer needs to be passed around. I'm not aware of any architectures that need floats aligned on 8-byte boundaries instead of 4-, but I wouldn't be shocked if there were some.

# ? Apr 7, 2009 17:42

newsomnuke: Feb 25, 2007

ShoulderDaemon posted:

Virtual members take up space because a function pointer needs to be passed around.

This'll be it. Isn't it a pointer to the vtable, though?

# ? Apr 7, 2009 18:00

ShoulderDaemon: Oct 9, 2003; support goon fund; Taco Defender

ultra-inquisitor posted:

This'll be it. Isn't it a pointer to the vtable, though?

As far as I know, compilers are free to implement vtables as either separate structures or inline with objects - if there's only a single virtual method, storing it inline saves an indirection, for example.

# ? Apr 7, 2009 18:06

Standish: May 21, 2001

ultra-inquisitor posted:

This'll be it. Isn't it a pointer to the vtable, though?

Are you on 64 bits?

# ? Apr 7, 2009 18:10

newsomnuke: Feb 25, 2007

Standish posted:

Are you on 64 bits?

Nah, bog-standard win32.

# ? Apr 7, 2009 18:15

schnarf: Jun 1, 2002; I WIN.

ultra-inquisitor posted:

code:
class Foo
{
	friend std::ostream& operator << (std::ostream& os, const Foo& a_var);

	int m_type;
	union
	{
		int m_int;
		float m_float;
	};
	
	// Member functions
	// ...
};
Why does sizeof(Foo) give me 12? Is there some odd padding going on, or is there something in the member functions which might be taking up space?

I'm betting the union isn't 4 bytes as you'd expect. The union size is basically up to the compiler. Somebody else can quote the spec better than I can, but the compiler is probably padding the union for whatever reason.

# ? Apr 7, 2009 19:29

digibawb: Dec 15, 2004; got moo?

schnarf posted:

I'm betting the union isn't 4 bytes as you'd expect.

How much you willing to bet?

It will be the vtable, as has already been covered.

# ? Apr 7, 2009 19:58

huge sesh: Jun 9, 2008

Is there any way to get the compiler to pretend that two enum types are one and the same? The situation I want is something like this:

code:

===base.h===
class base
{
  enum {
    a,
    b,
    c,
    base_last,
  } Activity;
};

===derived.h===
class derived : public base
{
  enum {
    d = base_last,
    e,
    f,
  };
};

Can I trick the compiler in some way into accepting d, e, and f as type Activity?

# ? Apr 8, 2009 06:16

Avenging Dentist: Oct 1, 2005; oh my god is that a circular saw that does not go in my mouth aaaaagh

No, that would be awful and violate the basic principle of enums (that they are a specific list of possible values).

# ? Apr 8, 2009 06:30

huge sesh: Jun 9, 2008

Avenging Dentist posted:

No, that would be awful and violate the basic principle of enums (that they are a specific list of possible values).

It's not my choice of how to do things, it's the way the Source engine works.

# ? Apr 8, 2009 06:38

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# ? Apr 29, 2024 18:16

Avenging Dentist: Oct 1, 2005; oh my god is that a circular saw that does not go in my mouth aaaaagh

huge sesh posted:

It's not my choice of how to do things, it's the way the Source engine works.

I doubt that the Source engine dictates that you use a language feature that does not exist.

# ? Apr 8, 2009 07:00

The Something Awful Forums > Discussion > Serious Hardware/Software Crap > The Cavern of COBOL > C/C++ Programming Questions Not Worth Their Own Thread

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