C / C++ / MFC

2-Jun-08 10:26

In a console app, I want to be able to test whether stdout and stderr are both printing to the screen. My output is messy unless I get it right (I'm printing to both stdout, and to stderr, and if they both happen to be the screen, I get two copies; I only want one copy on the screen).

A line like

<br />
if( stdout == stderr )<br />

always tests false under all the Windows compilers I've tried, so I get the duplication I'm trying to avoid.

Any ideas?

David
---------
Empirical studies indicate that 20% of the people drink 80% of the beer. With C++ developers, the rule is that 80% of the developers understand at most 20% of the language. It is not the same 20% for different people, so don't count on them to understand each other's code.
http://yosefk.com/c++fqa/picture.html#fqa-6.6
---------

David Crow2-Jun-08 11:01

David Crow

2-Jun-08 11:01

DQNOK wrote:
A line like

if( stdout == stderr )

always tests false under all the Windows compilers I've tried, so I get the duplication I'm trying to avoid.

What about:

if (&stdout == &stderr)

In any case, I would really expect them to not ever be *equal* even though they may resolve to the same location (i.e., screen).

"Love people and use things, not love things and use people." - Unknown

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

DQNOK2-Jun-08 11:11

2-Jun-08 11:11

DavidCrow wrote:
What about:

if (&stdout == &stderr)

That won't compile under Visual C++

The standard says that stdout and stderr are macros that evaluate to FILE pointer rvalues. Taking the address them seems suspicious from the outset...

Nibu babu thomas2-Jun-08 17:11

Nibu babu thomas

2-Jun-08 17:11

DQNOK wrote:
Any ideas?

Does GetStdHandle() help?

Nibu thomas
Microsoft MVP for VC++

Code must be written to be read, not by the compiler, but by another human being.

Programming Blog: http://nibuthomas.wordpress.com

DQNOK3-Jun-08 3:22

3-Jun-08 3:22

Nibu babu thomas wrote:
Does GetStdHandle() help?

I'll look into it. Thanks for the idea.

David

DQNOK3-Jun-08 8:43

3-Jun-08 8:43

Nibu babu thomas wrote:
Does GetStdHandle() help?

From reading the MSDN site, I thought it would; but it doesn't do what I thought.

   HANDLE  stderrHndl = GetStdHandle(STD_ERROR_HANDLE);
   HANDLE  stdoutHndl = GetStdHandle(STD_OUTPUT_HANDLE);

...
(very incomplete!)

   vfprintf( stderr, msg, args );

   if( stderrHndl == stdoutHndl ) //still ALWAYS tests FALSE
      goto logprint; //skip printing to stdout

   vfprintf( stdout, msg, args );
logprint:

Because the stderrHndl == stdoutHndl is always evaluating to FALSE, I'm still double printing to the console.

David

maxie20052-Jun-08 19:12

maxie2005

2-Jun-08 19:12

If your output is being flooded why dont you just re-direct stderr to a file.

console_app 2> stderr.log

DQNOK3-Jun-08 3:17

'LONG' to 'int' [modified]

3-Jun-08 3:17

I like that idea.

But this needs to be general. It's an "alert" library (a very minature logging library) that needs to detect on its own whether stderr has already been redirected.

Key idea: *auto-detect* where stderr is outputting to, and if it's going to stdout, skip over the requirement to write to stderr.

  vprintf( alertMsg, msgArgs );             //print to stdout
  if( stdout != stderr )
     vfprintf( stderr, alertMsg, msgArgs ); //print to stderr
//otherwise, already printed to stderr.  Just move on.
  ...

(Note: code is not complete; it needs some complicating va_end and va_starts in there to make it work correctly. Don't use it as a model!)

Queeny2-Jun-08 10:14

Queeny

2-Jun-08 10:14

I have a LONG variable, x, and I need to use the value as an int for my "for" loop.

for (int i; i<x; i++)
How do I typecast a 'LONG' variable to an 'int'?

When I declare "i" as a "LONG" variable as such

for (LONG i; i<x; i++)
I get this error: no conversion from 'LONG' to 'LONG'

What should I do?

Thanks.

modified on Monday, June 2, 2008 8:46 PM

<div class="ForumMod">modified on Monday, June 2, 2008 8:47 PM</div>

Mark Salsbery2-Jun-08 10:25

Mark Salsbery

2-Jun-08 10:25

Where's the code? Smile | :)

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Queeny2-Jun-08 14:43

Queeny

2-Jun-08 14:43

oups...forgot to ignore HTML tags

for (int i; i<variable; i++)
and

for (LONG i; i<variable; i++)

Mark Salsbery3-Jun-08 4:58

Mark Salsbery

3-Jun-08 4:58

You shouldn't have to do anything special to use the LONG.

There's no requirement to use int in a 'for' statement. You can actually
put any valid code you want to in the three expressions (init/condition/loop).

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

DQNOK2-Jun-08 10:36

2-Jun-08 10:36

It should work even as a type long (I'm not familiar with type LONG: if it's a composite type, then it won't work).

Any reason you can't just cast it to int at the point you are actually using it within the loop?

This should work (provided x is not a composite type)

for( x = someval; x < someotherval; x++ )
{
   ...
   i = (int)x; //cast x to int where it's actually needed.
}

Kwanalouie2-Jun-08 14:58

Kwanalouie

2-Jun-08 14:58

When I compile this code, it compiles with no errors (Visual C++ 6.0)

void test(void)
{
LONG x;

x = 800;
for (LONG i=0; i < x; i++)
{
}
}