C# Discussion Boards - CodeProject

27-Aug-02 22:20

How can I find out if some a file or a directory is access denied for read or write?

Mazy

"If I go crazy then will you still
Call me Superman
If I’m alive and well, will you be
There holding my hand
I’ll keep you by my side with
My superhuman might
Kryptonite"Kryptonite-3 Doors Down

Rickard Andersson²⁰27-Aug-02 22:30

Rickard Andersson²⁰

27-Aug-02 22:30

How about this if you check for a files read/write protection:

FileAttributes fa = File.GetAttributes(@"C:\TheFile.txt");
                                                                                         
if((fa & FileAttributes.ReadOnly) == FileAttributes.ReadOnly) // Write protected?
{
     // Yes it is!
}

Rickard Andersson@Suza Computing
C# and C++ programmer from SWEDEN!
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Mazdak28-Aug-02 1:39

28-Aug-02 1:39

ReadOnly attribute is not a file security.There are some directories or file that maybe you can't even read.

Mazy

"If I go crazy then will you still
Call me Superman
If I’m alive and well, will you be
There holding my hand
I’ll keep you by my side with
My superhuman might
Kryptonite"Kryptonite-3 Doors Down

leppie28-Aug-02 1:53

leppie

28-Aug-02 1:53

I saw a post about 2 weeks ago regarding the NTFS File Security attributes, unfortunately my GPRS connection takes ages to surf, so mite just wanna try a search for it or the article (metioned in the post) on CodeProject.

Hope u find it, else i'll post the link later Smile | :)

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Mazdak28-Aug-02 3:11

.Net framework source code

28-Aug-02 3:11

This article?:

NT Security Classes for .NET

Thank you.I'll check it out.Of course its MC++. Smile | :)

Mazy

"If I go crazy then will you still
Call me Superman
If I’m alive and well, will you be
There holding my hand
I’ll keep you by my side with
My superhuman might
Kryptonite"Kryptonite-3 Doors Down

27-Aug-02 21:53

Along with Anakrino, I recommend that one (MS shared source) to get to know how all this works behind the wheel,

Anyone ever tried to attach these symbols to a debug session by the way ?

-- modified at 10:59 Friday 14th October, 2005

find a string in another string

Mazdak27-Aug-02 20:55

Re: find a string in another string

27-Aug-02 20:55

How can I find out if a string exist in another string.Something like strstr in C++.

Mazy

"If I go crazy then will you still
Call me Superman
If I’m alive and well, will you be
There holding my hand
I’ll keep you by my side with
My superhuman might
Kryptonite"Kryptonite-3 Doors Down

Nnamdi Onyeyiri27-Aug-02 21:18

Nnamdi Onyeyiri

27-Aug-02 21:18

try using the IndexOf function in the string class, if the string is found, it will return the index of it, but if the string is not found, it will return -1. Smile | :)

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Re: find a string in another string

Mazdak27-Aug-02 22:20

Re: find a string in another string

27-Aug-02 22:20

Hmmmm,Good idea.Thanks. Smile | :)

Nnamdi Onyeyiri28-Aug-02 2:19

Nnamdi Onyeyiri

28-Aug-02 2:19

an alternative to that is to use te StrringBuilder class, but that would mean initialising extra variables that arent really needed.

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"All programmers are playwrights and all computers are lousy actors."

C# and null Structs?

Rodney S. Foley27-Aug-02 18:01

27-Aug-02 18:01

Why can't you set an instance of a struct to null? And therefore you cannot test a struct for null.

Which if this cannot be done really really sucks big time. I get compiler errors when I try to set an instance of a struct to null or test it for null.

I have checked my 3 C# books, and none of them even talk about it, and none of them never even use the word null in the book even once.

If this is true this is very stupid, it creates more work for some coding solutions.

In case it is important the struct in question is a "System.Drawing.Rectangle".

The errors:
#1: error CS0037: Cannot convert null to 'System.Drawing.Rectangle' because it is a value type

#2: error CS0019: Operator '==' cannot be applied to operands of type 'System.Drawing.Rectangle' and '<null>'

This is one reason I dislike structs.

Thanks,

Aalst

>> UPDATE

I figured a way around this. Setting a instance of a Rectangle to Rectangle.Empty, and then testing with IsEmpty property.

This works, but still doesn't tell me why, just that the implementor was prepared for it.

Anyway... still would like to know why (besides that it is a value type). Why Structs which are so similar to objects, and act like them in so many ways, can not act like them in this way thats all.

Thanks again,

Aalst

James T. Johnson27-Aug-02 18:18

James T. Johnson

27-Aug-02 18:18

structs and any other type that inherits from ValueType lives on the stack, and thus can't be null. ValueTypes are also copied by value instead of by reference, so assigning one System.Drawing.Rectangle to another only copies the values so any further changes to one won't affect the other.

Most struct based datatypes expose a static member named Empty which can be used for comparisons.

James
"And we are all men; apart from the females." - Colin Davies

Rodney S. Foley27-Aug-02 18:47

27-Aug-02 18:47

Thanks James for the detailed explaination.

:-D This is just me gripping about something that can't be changed now.  It is not directed at anyone. :-D

Then they should not allow the use of 'new' to create one. Like in C++ you should have a choice of where you want it to be. Stack or Heap by the use of the keyword 'new' or not. If they are not going to allow you to put the struct on the heap then it should be just like an int and you do not be allowed to use the keyword 'new'.

Don't get me wrong I like C# for somethings, but I think Microsoft's attempts to merge C++ and Java missed the mark in a lot of areas.

I think Java, C#, and C++ have there place in the world and never will any one replace another in it.

Anyway, enough of my gripping Mad | :mad:

about this stuff...

leppie27-Aug-02 21:33

leppie

27-Aug-02 21:33

Hi Aalst, I have these problems all the time and I went searching for for more info. This is especially in regards to calling unmanaged functions that can either take a null or a struct as a parameter.

Firstly ,if it can be worked around try overloading the function, else define the struct as a class , but with an expilcit layout attribute (sequencial allways). This way the unmanaged function is "tricked" in to believing it is a struct.

Info can be viewed HandleRef Sample[^].

Hope this help Smile | :)

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Rodney S. Foley28-Aug-02 8:18

28-Aug-02 8:18

I wasn't having this problem with unmanaged code, it was with the .NET Framework itself, and the fact that they include structs in it.

However, the first time I tried to use COM InterOp a while back, it required a struct. This created another problem I have with the .NET Framework, how it InterOps with COM. If you add a reference to a COM DLL you only get the classes and interfaces, you do not get any functions, structs or enums. This causes great problems when you have to re-create these structs & enums in C#. First for enums you have to hope they are declared in the Header file (and usually they are) so that you can get the correct values for each member. As for structs, if they are simple data structs then usually no problem. However, when the struct implements a C++ only feature lie "union" you are screwed.

The "union" keyword really should be part of C# it is useful in some situations, and if they are not going to wrap structs and enums in the COM InterOp then they should provide you everything that you need to recreate them.

So the first time I tried to use an unmanaged function the struct it required had a union in it. Which there is NO WAY to recreate this in C#. I know how to simulate a union in C# but it has it's limits and it can not be used with unmanaged code.

Again Microsoft didn't think hard enough on how they were going to implement something, and it causes people problems (usually me).

Also BTW "ms-help://" links are environment dependent. They do not work in IE Directly. They only work in a MS Help utility or application. Like Visual Studio or MSDN Library. So if you see something you like in one of those then you can get it from the ONLINE MSDN library and provide that link.

Sorry for all my gripping, but maybe someone at Microsoft will see it someday and provide fix the problems in a future Service Pack release. (yeah Right!)

Aalst

leppie28-Aug-02 8:52

leppie

28-Aug-02 8:52

Thanx for the insight Smile | :)

I do agree, there are some parts that I just like, but I guess they cant make a language perfect for everyone, hence .NET and the ability to write in the language of choice, depending on the situation.

Aalst wrote:
Also BTW "ms-help://" links are environment dependent. They do not work in IE Directly.

Funny, mine does. Smile | :)

MYrc : A .NET IRC client with C# Plugin Capabilities. See
http://sourceforge.net/projects/myrc for more info. Big Grin | :-D

Alastair Stell27-Aug-02 21:52

Alastair Stell

27-Aug-02 21:52

The simplest solution is instantiate the structure as an object rather than as a structure. You can always use and explicit cast to get it back to a structure.

Only change is constant

Rodney S. Foley28-Aug-02 7:50

28-Aug-02 7:50

Casting a sturct to an object is to much overhead. I would have to cast it every time it is needed. Thanks for the advice though.

All structs in the .NET Framework seem to have ways around this problem, by providing a static EMPTY member that you use like setting an object to null, and an IsEmpty property for testing against like testing against a null object. Only have to worry about 3rd party structs. I do not create structs in my code, since I do not like them. I use classes not structs.

In my opinion the only useful struct is one that does not have constructors or methods, just public members for use a simple data structure. To do more than this, you should just design it as a class not a struct. Struct's are from pre-OOD, and they should not have been brought into a new OO language. They have reasons for being in C++ for backwards compatibility, but they have no usefulness in C#.

Again this is just more of my ranting about a bad design choice on Microsoft part.

Aalst

Alastair Stell29-Aug-02 4:48

Alastair Stell

29-Aug-02 4:48

Coming from a pure object oriented background (smalltalk and eiffel) I am very sympathetic to your view. Like you I mostly avoid using structures. When I do create structures I generally employ 'new', and I mostly use them for interop with Windows API's.

Obviously value types were retained for speed optimizations and because the second you drop below the rather spartan GDI+ abstraction you will be making extensive use of structures.

Unfortunately C# is still a hybrid language - for instance, it is not truly polymorphic. And it does not use messaging as its primary medium for communicating between objects. However, the inclusion of the Interface 'pattern' has gone some way towards alleviating the lack of full polymorphism. And it does encourage a rather nice 'published' approach to defining component interfaces. I wish that metadata manipulation were a shade better developed. On the odd occasion I cannot be bothered to write an Interface I end up using the 'is' keyword and casting objects to specific class types. Which is a bit of a bore really.

Studio .NET is really just a two trick pony. C# is the primary language and C++ is retained for those occasions you really must drop down to API level (I use C++ to wrap DirectX API code for instance).

VB.NET is just C# with VB-like syntax. Likewise J#. Except that J# is essentially useless to serious Java programmers because it has no support for VM/Swing. I also mourn losing FoxPro database. But hey, that's life.

Only change is constant

Rodney S. Foley29-Aug-02 9:49