473,320 Members | 1,732 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,320 software developers and data experts.

evalutation order for logical operators

Hi,

I wondering if there is a standard specification for evalutation of
logical expressions. For instance:

if (p != NULL && strlen(p) x )
do_something();

If p is actually NULL, should this code (built with a generic
compiler) crash?
Considering that the first element is FALSE, evalutation of strlen()
is useless, so it (theoretically) should be skipped...
My compiler (gcc) works as I expected, is it a standard behaviour?

Thanks,

s.

Nov 5 '07 #1
3 1875
gallows wrote:
>
Hi,

I wondering if there is a standard specification for evalutation of
logical expressions.
N869
6.5.13 Logical AND operator
[#4] Unlike the bitwise binary & operator, the && operator
guarantees left-to-right evaluation; there is a sequence
point after the evaluation of the first operand. If the
first operand compares equal to 0, the second operand is not
evaluated.
For instance:

if (p != NULL && strlen(p) x )
do_something();

If p is actually NULL, should this code (built with a generic
compiler) crash?
No.
Considering that the first element is FALSE, evalutation of strlen()
is useless, so it (theoretically) should be skipped...
My compiler (gcc) works as I expected, is it a standard behaviour?
Yes.

--
pete
Nov 5 '07 #2
gallows <g4ll...@gmail.comwrote:
Hi,

I wondering if there is a standard specification for evalutation of
logical expressions. For instance:

if (p != NULL && strlen(p) x )
do_something();
This is a FAQ...

http://c-faq.com/expr/shortcircuit.html

--
Peter

Nov 5 '07 #3
On 5 Nov, 02:52, Peter Nilsson <ai...@acay.com.auwrote:
gallows <g4ll...@gmail.comwrote:
Hi,
I wondering if there is a standard specification for evalutation of
logical expressions. For instance:
if (p != NULL && strlen(p) x )
do_something();

This is a FAQ...

http://c-faq.com/expr/shortcircuit.html

--
Peter
Ouch, I'm sorry.
Thanks!

Nov 5 '07 #4

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

3
by: Andrew Durdin | last post by:
In Python, you can override the behaviour of most operators for a class, by defining __add__, __gt__, and the other special object methods. I noticed that, although there are special methods for...
8
by: der | last post by:
Hello all, I've a question about order of evaluations in expressions that have && and || operators in them. The question is: will the evalution go left-to-right, no matter what -- even if the...
13
by: Richard | last post by:
Boy, I'll sure bet this is a FAQ. Many years ago, my "runtime behavior of programming languages" prof absolutely guaranteed that C parameters are evaluated left-to-right. He was a bright guy...
13
by: Ravi Uday | last post by:
Hi, -I have some confusion on the order in which the operators are evaluated. A statement such as 7/9*9+6-4 is evaluated in which order ? -Which of the following is evaluated first: a) && b)...
80
by: Christopher Benson-Manica | last post by:
Of course one can get the effect with appropriate use of existing operators, but a ^^ operator would make for nice symmetry (as well as useful to me in something I'm working on). Am I the only one...
2
by: ThunderMusic | last post by:
Hi, I have a value that contains flags that I must get using a bitmask. I tryied with the && operator, but the compiler outputs this error : Operator '&&' cannot be applied to operands of type...
3
by: andreas ames | last post by:
Hi all, recently I came across a line of code like the following: if seq.erase(seq.begin(), seq.end()) != seq.end() /* ... */ It made me wonder if this is just bogus or if it even can...
13
by: TheLostLeaf | last post by:
Hi, Does anyone know if these 2 code segments would operate the same way. for instance if the first condition fails does it bother to check the second? if (MyList.Count 0 && CheckDate) {
54
by: Rasjid | last post by:
Hello, I have just joined and this is my first post. I have never been able to resolve the issue of order of evaluation in C/C++ and the related issue of precedence of operators, use of...
0
by: DolphinDB | last post by:
Tired of spending countless mintues downsampling your data? Look no further! In this article, you’ll learn how to efficiently downsample 6.48 billion high-frequency records to 61 million...
0
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
1
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
0
by: Vimpel783 | last post by:
Hello! Guys, I found this code on the Internet, but I need to modify it a little. It works well, the problem is this: Data is sent from only one cell, in this case B5, but it is necessary that data...
0
by: jfyes | last post by:
As a hardware engineer, after seeing that CEIWEI recently released a new tool for Modbus RTU Over TCP/UDP filtering and monitoring, I actively went to its official website to take a look. It turned...
1
by: PapaRatzi | last post by:
Hello, I am teaching myself MS Access forms design and Visual Basic. I've created a table to capture a list of Top 30 singles and forms to capture new entries. The final step is a form (unbound)...
1
by: CloudSolutions | last post by:
Introduction: For many beginners and individual users, requiring a credit card and email registration may pose a barrier when starting to use cloud servers. However, some cloud server providers now...
1
by: Defcon1945 | last post by:
I'm trying to learn Python using Pycharm but import shutil doesn't work
1
by: Shællîpôpï 09 | last post by:
If u are using a keypad phone, how do u turn on JavaScript, to access features like WhatsApp, Facebook, Instagram....

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.