What is the result of that?
I am reimplementing the C library, and I would like to know.
Now I have it to return zero. Is that correct?
The standard says:
The strncmp function compares not more than n characters (characters
that follow a
null character are not compared) from the array pointed to by s1 to the
array pointed to
by s2.
Returns
The strncmp function returns an integer greater than, equal to, or less
than zero,
accordingly as the possibly null-terminated array pointed to by s1 is
greater than, equal
to, or less than the possibly null-terminated array pointed to by s2.
(7.21.4.4 page 328)
The zero case is not mentioned.
The comparison of no characters is always equal... (What a nonsense
isn't it?). But I *have* to return something. 9 1877
In article <41************ ***********@new s.wanadoo.fr>,
jacob navia <ja***@jacob.re mcomp.fr> wrote: What is the result of that?
I am reimplementing the C library, and I would like to know.
Now I have it to return zero. Is that correct?
The standard says: >>
snip The zero case is not mentioned.
The comparison of no characters is always equal... (What a nonsense isn't it?). But I *have* to return something.
It is mentions it in the text describing the header file 7.21.1#2.
Where an argument declared as size_t n specifies the length of the arrray
for a function, n can have the value zero on a call to that function.
......
On such a call, ...., a function that compares two character sequences
returns zero, ....
Hope that helps.
Kevin.
jacob navia wrote: What is the result of that?
I am reimplementing the C library, and I would like to know.
Now I have it to return zero. Is that correct?
The standard says: >> The strncmp function compares not more than n characters (characters that follow a null character are not compared) from the array pointed to by s1 to the array pointed to by s2. Returns The strncmp function returns an integer greater than, equal to, or less than zero, accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal to, or less than the possibly null-terminated array pointed to by s2. (7.21.4.4 page 328) >>
The zero case is not mentioned.
The comparison of no characters is always equal... (What a nonsense isn't it?). But I *have* to return something.
Return a zero. Section 7.21.1, paragraph 2 describes
what happens with zero lengths:
[...] On such a call [...] a function that compares
two character sequences returns zero, [...]
-- Er*********@sun .com
OK. Thanks, I did not see that one
jacob navia wrote: What is the result of that?
of what? I am reimplementing the C library, and I would like to know. Now I have it to return zero. Is that correct? The standard says:
Snipped and requoted in a legible manner:
7.21.4.4 The strncmp function
Synopsis
[#1]
#include <string.h>
int strncmp(const char *s1, const char *s2, size_t n);
Description
[#2] The strncmp function compares not more than n
characters (characters that follow a null character are not
compared) from the array pointed to by s1 to the array
pointed to by s2.
Returns
[#3] The strncmp function returns an integer greater than,
equal to, or less than zero, accordingly as the possibly
null-terminated array pointed to by s1 is greater than,
equal to, or less than the possibly null-terminated array
pointed to by s2. The zero case is not mentioned.
The comparison of no characters is always equal... (What a nonsense isn't it?). But I *have* to return something.
Don't you think one empty string is equal to another empty string?
How about (untested):
while (*s1 && (*s1 == *s2) && n) {
s1++; s2++; n--;
}
return ((*s1 > *s2) - (*s1 < *s2)) && n;
The final comparison may need casts to unsigned. As the standard
reads it would seem that signed chars would be allowed to affect
the result, but there may be a clause specifying this somewhere.
This should be fodder for gccs optimizer or a good assembly
programmer.
--
Chuck F (cb********@yah oo.com) (cb********@wor ldnet.att.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home .att.net> USE worldnet address!
CBFalconer wrote: jacob navia wrote: What is the result of that?
of what?
I am reimplementing the C library, and I would like to know. Now I have it to return zero. Is that correct? The standard says:
Snipped and requoted in a legible manner:
7.21.4.4 The strncmp function
Synopsis
[#1] #include <string.h> int strncmp(const char *s1, const char *s2, size_t n);
Description
[#2] The strncmp function compares not more than n characters (characters that follow a null character are not compared) from the array pointed to by s1 to the array pointed to by s2.
Returns
[#3] The strncmp function returns an integer greater than, equal to, or less than zero, accordingly as the possibly null-terminated array pointed to by s1 is greater than, equal to, or less than the possibly null-terminated array pointed to by s2.
The zero case is not mentioned.
The comparison of no characters is always equal... (What a nonsense isn't it?). But I *have* to return something.
Don't you think one empty string is equal to another empty string? How about (untested):
while (*s1 && (*s1 == *s2) && n) { s1++; s2++; n--; } return ((*s1 > *s2) - (*s1 < *s2)) && n;
return ((*s1 > *s2) - (*s1 < *s2)) && n;
The final comparison may need casts to unsigned. As the standard reads it would seem that signed chars would be allowed to affect the result, but there may be a clause specifying this somewhere. This should be fodder for gccs optimizer or a good assembly programmer.
In the final comparison, the pointers need to be cast
to type pointer to unsigned char.
If char is signed and *s1 equals -1 and *s2 equals -2,
then which one compares greater,
depends on the representation of negative integers.
--
pete
pete wrote: CBFalconer wrote: while (*s1 && (*s1 == *s2) && n) { s1++; s2++; n--; } return ((*s1 > *s2) - (*s1 < *s2)) && n;
strncpy is not supposed to compare more than n characters.
I don't see what difference it could make
if strncpy was implemented as above instead.
Apparently I added the following line accidentally.
return ((*s1 > *s2) - (*s1 < *s2)) && n;
--
pete
pete wrote: pete wrote: CBFalconer wrote:
while (*s1 && (*s1 == *s2) && n) { s1++; s2++; n--; } return ((*s1 > *s2) - (*s1 < *s2)) && n;
strncpy is not supposed to compare more than n characters.
^^
strncmp
--
pete
In <41************ ***********@new s.wanadoo.fr> jacob navia <ja***@jacob.re mcomp.fr> writes: OK. Thanks, I did not see that one
Because you don't know how to read the C standard. Individual
function descriptions MUST be read in the context set by the introductory
paragraph(s) of each section.
Dan
--
Dan Pop
DESY Zeuthen, RZ group
Email: Da*****@ifh.de
Currently looking for a job in the European Union This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
by: pembed2003 |
last post by:
Hi,
I have an application where I use the strncmp function extensively to
compare 2 string to see if they are the same or not. Does anyone know
a faster replacement for strncmp? I notice there is a memncmp function
which is very fast but it doesn't work the same like strncmp so I
don't think I can use it. I also tried to write the string_equal
function myself like:
int string_equal(const char* s1,const char* s2){
while(*s1 && *s2 &&...
|
by: Bert |
last post by:
I have a question about buffer overflows with strcmp or strncmp
(strnicmp). It's best described by providing an example
Example:
There is a string "sBuf" of length 5000. In a for loop from 0 to 5000,
several NUL terminated strings are compared, these strings vary in size
from 3 to 9.
sBuf is user input (a file), memory is dynamically allocated using
malloc (file length+1) and it is properly nul terminated. The other
|
by: Preets |
last post by:
Hi,
Can anybody please tell me the difference between memcmp() and
strncmp() functions ?
|
by: arunraj2002in |
last post by:
Hi All,
I have doubt in strncmp.
consider the following prog:
int main()
{
int i;
i = strncmp("Nstring","Astring",6);
|
by: Krumble Bunk |
last post by:
Hi all,
Having some trouble with a seemingly-simple task. Need to have a
basic CLI functionality as per:
prompt <- \n
prompt <- \n
promptquit <- should quit as per my snippet, but doesn't.
I've thrown a few random fflush()'s in, but no joy. I have never
| |
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can effortlessly switch the default language on Windows 10 without reinstalling. I'll walk you through it.
First, let's disable language synchronization. With a Microsoft account, language settings sync across devices. To prevent any complications,...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers, it seems that the internal comparison operator "<=>" tries to promote arguments from unsigned to signed.
This is as boiled down as I can make it.
Here is my compilation command:
g++-12 -std=c++20 -Wnarrowing bit_field.cpp
Here is the code in...
|
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven tapestry of website design and digital marketing. It's not merely about having a website; it's about crafting an immersive digital experience that captivates audiences and drives business growth.
The Art of Business Website Design
Your website is...
|
by: Hystou |
last post by:
Overview:
Windows 11 and 10 have less user interface control over operating system update behaviour than previous versions of Windows. In Windows 11 and 10, there is no way to turn off the Windows Update option using the Control Panel or Settings app; it automatically checks for updates and installs any it finds, whether you like it or not. For most users, this new feature is actually very convenient. If you want to control the update process,...
|
by: conductexam |
last post by:
I have .net C# application in which I am extracting data from word file and save it in database particularly. To store word all data as it is I am converting the whole word file firstly in HTML and then checking html paragraph one by one.
At the time of converting from word file to html my equations which are in the word document file was convert into image.
Globals.ThisAddIn.Application.ActiveDocument.Select();...
|
by: TSSRALBI |
last post by:
Hello
I'm a network technician in training and I need your help.
I am currently learning how to create and manage the different types of VPNs and I have a question about LAN-to-LAN VPNs.
The last exercise I practiced was to create a LAN-to-LAN VPN between two Pfsense firewalls, by using IPSEC protocols.
I succeeded, with both firewalls in the same network. But I'm wondering if it's possible to do the same thing, with 2 Pfsense firewalls...
| |
by: adsilva |
last post by:
A Windows Forms form does not have the event Unload, like VB6. What one acts like?
|
by: 6302768590 |
last post by:
Hai team
i want code for transfer the data from one system to another through IP address by using C# our system has to for every 5mins then we have to update the data what the data is updated we have to send another system
|
by: bsmnconsultancy |
last post by:
In today's digital era, a well-designed website is crucial for businesses looking to succeed. Whether you're a small business owner or a large corporation in Toronto, having a strong online presence can significantly impact your brand's success. BSMN Consultancy, a leader in Website Development in Toronto offers valuable insights into creating effective websites that not only look great but also perform exceptionally well. In this comprehensive...
| | |