This is the mail archive of the mailing list for the GCC project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

RE: Missing warning about uninitialized variable.

Just a quick question: Did anybody actually read the subject? My question
was not about the value of the variable, it was about recent GCC versions no
longer warn about the use of an uninitialized variable...?


-----Original Message-----
From: [] On
Behalf Of Tom St Denis
Sent: den 29 november 2007 19:12
To: J.C. Pizarro
Subject: Re: Missing warning about uninitialized variable.

J.C. Pizarro wrote:
> My input's sequence for the program was { 1 to 10, 1 to 10, 1 to 10, 1
> to 10, 1 to 10 }
> and the output's sequence was { sequence of random data and inestimable }.
Ok, first off, I'm a cryptographer so "random" has an actual meaning to 
me, as oppose to "undetermined."

Second, there is a difference between "undefined" and "random." 

Third, those numbers are NOT random.  5 32-bit numbers should have quite 
a few different bits between them.  If I took two 32-bit numbers I'd 
expect on average at least 16 bits to be different between them (well 
more so, that'd be the most likely outcome).

Fourth, it's not a "random process."  The compiled instance of your 
undefined code will follow a very logical and predictable course given 
the current contents of unitialized memory. 

suppose in

int a;
printf("a = %d\n", a);

The memory for "a" contained the int "5" . This is undefined code, as 
in, the standard has no prescribed behaviour for the resulting program.  
However, it WILL print "5" every time the "a" variable contains 5.  It 
WILL do that.  As in, it's NOT a random process.

>> int a;
>> printf("a == %d\n", a);
>> That's not "random," nor is it "stochastic," or even "perplexing!" for
>> that matter.  It's undefined.  I can't tell you what that will print.
>> But I can justify what it did print [if that makes any sense...].
>> Tom
> It's not a "functional programming", it's an "imperative programming",
> they are different.

Use terminology from the standard if you're going to use anything.  What 
I wrote is a syntactically correct program (hence it compiles).  It's 
just not going to produce a defined behaviour (since a is uninitialized).

Here is your homework list of words to learn

- undefined
- defined
- behaviour
- deterministic
- initialized [and uninitialized]

I understand that English is likely not your first language, but please 
stop trying to invent new terminology.  Explain what you mean in simple 
English, and we can help you explain it in terminology prescribed by the 


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]