File pointers ot unmanaged code ??

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G

Guest

Hi,

Can we send File pointers from managed code to a method in unmanaged code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
 
*ANY* pointers that you need to marshal across the interop boundary can be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil
 
*But* the pointer must be valid and have the same meaning in both spaces.
You can pass a, unmanaged FILE * as an IntPtr, but if you're asking if you
can pass a System.IO.File to unmanaged code, then I'm not nearly as inclined
to say "yes." Where is the handle coming from in the managed code? Another
P/Invoke?

-Chris


Neil Cowburn said:
*ANY* pointers that you need to marshal across the interop boundary can be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil

Naveen Mukkelli said:
Hi,

Can we send File pointers from managed code to a method in unmanaged code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
Click to expand...
Click to expand...
 
I concur wholeheartedly. That's why I included the snippet about getting the
FILE * through P/Invoke. The IntPtr *absolutely, must, without a doubt* be a
FILE * for it to work.


Chris Tacke said:
*But* the pointer must be valid and have the same meaning in both spaces.
You can pass a, unmanaged FILE * as an IntPtr, but if you're asking if you
can pass a System.IO.File to unmanaged code, then I'm not nearly as
inclined
to say "yes." Where is the handle coming from in the managed code?
Another
P/Invoke?

-Chris


Neil Cowburn said:
*ANY* pointers that you need to marshal across the interop boundary can
be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil

Naveen Mukkelli said:
Hi,

Can we send File pointers from managed code to a method in unmanaged code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
Click to expand...
Click to expand...
Click to expand...
 
Hi Neil,

Thanks for the reply. I'm having problems in opening the file.

when I tried using


[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

I am getting "A native exception has ouccurred in xxx.exe"
ExceptionCode: 0xc0000005
ExceptionAddress: 0x013a1350
Reading: 0x2a000300

Could you please explain what exactly is happening here.

Cheers,

Naveen.


Neil Cowburn said:
*ANY* pointers that you need to marshal across the interop boundary can be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil

Naveen Mukkelli said:
Hi,

Can we send File pointers from managed code to a method in unmanaged code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
Click to expand...
Click to expand...
 
Your second parameter should be a string so change your code to:-
[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, string pchAccessMode);

Peter

--
Peter Foot
Windows Embedded MVP
www.inthehand.com | www.opennetcf.org

Do have an opinion on the effectiveness of Microsoft Windows Mobile and
Embedded newsgroups? Let us know!
https://www.windowsembeddedeval.com/community/newsgroups

Naveen Mukkelli said:
Hi Neil,

Thanks for the reply. I'm having problems in opening the file.

when I tried using


[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

I am getting "A native exception has ouccurred in xxx.exe"
ExceptionCode: 0xc0000005
ExceptionAddress: 0x013a1350
Reading: 0x2a000300

Could you please explain what exactly is happening here.

Cheers,

Naveen.


Neil Cowburn said:
*ANY* pointers that you need to marshal across the interop boundary can
be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil

Naveen Mukkelli said:
Hi,

Can we send File pointers from managed code to a method in unmanaged
code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
Click to expand...
Click to expand...
Click to expand...
 
Hi Peter,

I did declare as you have mentioned!!

I am using the declreration as follows..
IntPtr fptr = IntPtr.Zero;
fptr = fopen("\\My Documents\\ErrorLog.txt","w");

It is working when I tried with "msvcr71.dll" on the PC.

did I forget anything else? Kindly let me know.

Cheers,

Naveen.

Peter Foot said:
Your second parameter should be a string so change your code to:-
[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, string pchAccessMode);

Peter

--
Peter Foot
Windows Embedded MVP
www.inthehand.com | www.opennetcf.org

Do have an opinion on the effectiveness of Microsoft Windows Mobile and
Embedded newsgroups? Let us know!
https://www.windowsembeddedeval.com/community/newsgroups

Naveen Mukkelli said:
Hi Neil,

Thanks for the reply. I'm having problems in opening the file.

when I tried using


[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

I am getting "A native exception has ouccurred in xxx.exe"
ExceptionCode: 0xc0000005
ExceptionAddress: 0x013a1350
Reading: 0x2a000300

Could you please explain what exactly is happening here.

Cheers,

Naveen.


Neil Cowburn said:
*ANY* pointers that you need to marshal across the interop boundary can
be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil

message Hi,

Can we send File pointers from managed code to a method in unmanaged
code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
Click to expand...
Click to expand...
Click to expand...
 
Hi Peter,

It seems that this is working in .NET Framework.
but It is not working in .NET Compact Framework.
my application will run on a PDA.

Could you suggest me how can I open a file in a PDA.

Cheers,

Naveen.


Peter Foot said:
Your second parameter should be a string so change your code to:-
[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, string pchAccessMode);

Peter

--
Peter Foot
Windows Embedded MVP
www.inthehand.com | www.opennetcf.org

Do have an opinion on the effectiveness of Microsoft Windows Mobile and
Embedded newsgroups? Let us know!
https://www.windowsembeddedeval.com/community/newsgroups

Naveen Mukkelli said:
Hi Neil,

Thanks for the reply. I'm having problems in opening the file.

when I tried using


[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

I am getting "A native exception has ouccurred in xxx.exe"
ExceptionCode: 0xc0000005
ExceptionAddress: 0x013a1350
Reading: 0x2a000300

Could you please explain what exactly is happening here.

Cheers,

Naveen.


Neil Cowburn said:
*ANY* pointers that you need to marshal across the interop boundary can
be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil

message Hi,

Can we send File pointers from managed code to a method in unmanaged
code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
Click to expand...
Click to expand...
Click to expand...
 
Hi Peter,

I could open a file and write to it successfully.
But I am having trouble in reading from the file.

I am using "coredll.dll" and .NET Compact Framework and C#.
This is how I am trying to read from a file.

[DllImport("coredll.dll")]
public static extern char[] fgets( char[] buffer, int max_length, IntPtr
fPtr);

[DllImport("coredll.dll")]
public static extern IntPtr fopen( byte[] fname, byte[] fmode);

[DllImport("coredll.dll")]
public static extern int fclose(IntPtr fname);


// I am converting a file name string in to unicode byte array.
private byte[] getByteArray(string str, ASCIIEncoding ae)
{
byte[] result = null;
int str_size = str.Length;
result = new byte[str_size];
if( (ae.GetBytes(str,0,str_size,result,0)== 0 ) )
{
result = null;
}
return result;
}

now I am calling the methods in this way.

byte[] fname = getByteArray("fileName", ae);
byte[] mode = getByteArray("r",ae);
IntPtr fptr = fopen(fname,mode);
char[] buffer;

fgets( buffer,255,fptr);

Then I am getting "NotSupportedException".

Could you please let me know where I went wrong.
I am opening the file properly. Is there any better way of opening
a file, convering a string to unicode string.

Cheers,

Naveen.




Peter Foot said:
Your second parameter should be a string so change your code to:-
[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, string pchAccessMode);

Peter

--
Peter Foot
Windows Embedded MVP
www.inthehand.com | www.opennetcf.org

Do have an opinion on the effectiveness of Microsoft Windows Mobile and
Embedded newsgroups? Let us know!
https://www.windowsembeddedeval.com/community/newsgroups

Naveen Mukkelli said:
Hi Neil,

Thanks for the reply. I'm having problems in opening the file.

when I tried using


[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

I am getting "A native exception has ouccurred in xxx.exe"
ExceptionCode: 0xc0000005
ExceptionAddress: 0x013a1350
Reading: 0x2a000300

Could you please explain what exactly is happening here.

Cheers,

Naveen.


Neil Cowburn said:
*ANY* pointers that you need to marshal across the interop boundary can
be
send as IntPtr.

In this case, your method P/Invoke signature would be:

[DllImport("somedll")]
public static extern int SomeMethod(IntPtr fptr, uint len);

You can P/Invoke fopen in coredll to get the FILE*,e.g.

[DllImport("coredll")]
static extern IntPtr fopen(string pchFileName, pchAccessMode);

IntPtr fptr = fopen("\\My Documents\\SomeFile.ext","r");

HTH
Neil

message Hi,

Can we send File pointers from managed code to a method in unmanaged
code
at all ?

One of the methods in the DLL I am using requires a file pointer as its
arguments.
The signature of the method in the DLL looks like this,

int SomeMethod( File *fptr, uint len ); ( C method )

How can we call this method from C#,
I mean,

[DllImport (" someDll.dll", CharSet = CharSet.Auto)]
public static extern int SomeMethod( ?, uint len );

Kindly let me know,

Cheers,

Naveen.
Click to expand...
Click to expand...
Click to expand...
 
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