Solved

simple C question

Posted on 2006-06-26
12
689 Views
Last Modified: 2010-04-15
Hi

I am looking at some legacy c code and i have come across

 list += temp + "\05" + " 0" + "\02";


what is "\05"  ,  "\02"

are these hex constants, binary constants, octal constants ?

thanks

0
Comment
Question by:Vlearns
  • 3
  • 2
  • 2
  • +3
12 Comments
 
LVL 37

Accepted Solution

by:
Harisha M G earned 500 total points
ID: 16988121
Hi, They are octal constants, but no matter what they are, their value remains the same :-)

---
Harish
0
 
LVL 37

Expert Comment

by:Harisha M G
ID: 16988143
0
 
LVL 16

Expert Comment

by:PaulCaswell
ID: 16988154
Hi Vlearns,

>> list += temp + "\05" + " 0" + "\02";
This isnt valid C. It might be C++ but not C.

This would be:

 list += temp + '\05' + '0' + '\02';
But even that seems wrong because that would be the same as:

 list += temp + 5 + '0' + 2;

Are you sure you copied it right?

Paul
0
NAS Cloud Backup Strategies

This article explains backup scenarios when using network storage. We review the so-called “3-2-1 strategy” and summarize the methods you can use to send NAS data to the cloud

 
LVL 45

Expert Comment

by:Kdo
ID: 16988162
Hi Vlearns,

That isn't legal syntax in modern C.  "\05" is not a character or integer value, it is a string pointer.  The keyword here is pointer.

As legacy code, it MAY have worked on old 8 and/or 16 bit systems, but it certainly isn't ANSI C in today's world.

However, replacing the double quotes with single quotes is a different matter.  (Note the spaced deleted from the " 0" string.)

 list += temp + '\05' + '0' + '\02';

In this case, the \05 and \02 are treated as octal contants so 5 and 2 are added to '0', giving the ASCII character '7'.



Good Luck!
Kent
0
 
LVL 16

Expert Comment

by:PaulCaswell
ID: 16988181
Snap! :-)
0
 
LVL 37

Expert Comment

by:Harisha M G
ID: 16988199
Vlearns, yeah I forgot.. as others said, it is valid only in C++ using string class.


0
 
LVL 2

Expert Comment

by:davidnsc1
ID: 16988460
It could be the tragic, pointless addition of string pointers :D
0
 
LVL 22

Expert Comment

by:grg99
ID: 16992373
it depends on whether this is compiled by a C compiler or a C++ compiler.
 list += temp + "\05" + " 0" + "\02";



If it is a C compiler, then the code doesnt make any sense,  as others have noted, adding double quoted strings doesnt do anything useful in C.  You end up with the sum of the addresses of some short strings, which is of no use that I can fathom.

If it's a C++ compiler, then it does make sense if "list" and "temp" are string-type variables.  Although the constants are might peculiar- an escaped zero is just a zero, and doesnt need the escaping.  

Maybe you can give us some more info, like the type of compiler, the name of this file, (.c or .cpp or what), the types of list and temp.

0
 
LVL 7

Expert Comment

by:aib_42
ID: 16999506
Here, let me back up everyone who has said this isn't valid C:

Pointer addition is invalid per §6.3.6 of ANSI 9899.
0
 
LVL 7

Expert Comment

by:aib_42
ID: 16999584
"\05", " 0" and "\02" are all string literals - the first and the last are arrays containing one character each: '\05' and '\02', respectively. (Which are octal character constants representing the ASCII characters ENQ and STX, respectively, as per mgh's reference.) The one in the middle is a two-character array containing the characters ' ' (the space) and '0' (the digit).

Maybe they are all character constants, and the one in the middle is a mistranslated \00?
0

Featured Post

Master Your Team's Linux and Cloud Stack

Come see why top tech companies like Mailchimp and Media Temple use Linux Academy to build their employee training programs.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

An Outlet in Cocoa is a persistent reference to a GUI control; it connects a property (a variable) to a control.  For example, it is common to create an Outlet for the text field GUI control and change the text that appears in this field via that Ou…
This is a short and sweet, but (hopefully) to the point article. There seems to be some fundamental misunderstanding about the function prototype for the "main" function in C and C++, more specifically what type this function should return. I see so…
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use for-loops in the C programming language.
The goal of this video is to provide viewers with basic examples to understand and use switch statements in the C programming language.

813 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

15 Experts available now in Live!

Get 1:1 Help Now