Re: C# - getting binary data from .lib
- From: "Michael Phillips, Jr." <mphillips53@xxxxxxxxxxxxxxx>
- Date: Sat, 3 Jun 2006 16:09:12 -0400
I am sorry that was a typo. Use (unsigned char*) rather than (char*).
What you are trying to accomplish is to let the wrapper internally call the
library to allocate memory for the image when a null pointer is passed as an
argument.
The library should return the pointer to this allocated memory. In "C",
this is accomplished by passing a pointer to a pointer on the stack.
In C# you are passing the address to a null pointer. You should get back an
unmanaged pointer with the allocated image.
"Stephen Cawood" <cawood@xxxxxxxxxx> wrote in message
news:4nlgg.24072$JX1.915@xxxxxxxxxxx
BTW - the binary data is used to create .PGM image files.
"Stephen Cawood" <cawood@xxxxxxxxxx> wrote in message
news:nhlgg.24033$JX1.23566@xxxxxxxxxxx
thanks again, I really appreciate the help. this problem has been a real
pain.
I tried your suggestion, but it didn't work. however, I feel that I might
be very close.
label1.Text = create_wrapped(0,5,ref ptrImage).ToString();
// returned -1 meaning that there was a problem
my original wrapper function was:
WIN32DLL_API int create_wrapped(int id, int scale, unsigned char *image)
{
return create(id, scale, image);
}
so I tried changing that to:
WIN32DLL_API int create_wrapped(int id, int scale, void** image)
{
return create(id, scale, (unsigned char*)*image);
}
your suggestion wouldn't compile:
WIN32DLL_API int create_wrapped(int id, int scale, void** image)
{
return create(id, scale, (char*)*image);
}
the error was: Cannot convert argument 3 from char* to unsigned char*
"Michael Phillips, Jr." <mphillips53@xxxxxxxxxxxxxxx> wrote in message
news:%23EGjMdzhGHA.1508@xxxxxxxxxxxxxxxxxxxxxxx
Your wrapper function should have the argument typed as a pointer to a
pointer for this to work correctly.
[DllImport("Wrapper.dll", EntryPoint="create_wrapped")]
public static extern int create_wrapped(int id, int scale, [In][Out] ref
IntPtr image);
WIN32DLL_API int create_wrapped(int id, int scale, void** image)
{
return create(id, scale, (char*)*image);
}
You call it as follows:
IntPtr ptrImage = IntPtr.Zero;
label1.Text = create_wrapped(0,5,ref ptrImage);
and of course check for a null pointer return.
"Stephen Cawood" <cawood@xxxxxxxxxx> wrote in message
news:o1jgg.23800$JX1.19291@xxxxxxxxxxx
I thought that you might be on to something, but sadly it didn't work.
thanks for the help though.
[DllImport("Wrapper.dll", EntryPoint="create_wrapped")]
public static extern int create_wrapped(int id, int scale, [In][Out]
ref IntPtr image);
IntPtr ptrImage = new IntPtr();
label1.Text = create_wrapped(0,5,ref ptrImage).ToString(); //this
crashes the debugger with no exception returned, I tried to catch it
but that didn't help
"Michael Phillips, Jr." <mphillips53@xxxxxxxxxxxxxxx> wrote in message
news:uJyWUbyhGHA.4044@xxxxxxxxxxxxxxxxxxxxxxx
You could try the same argument semantics used by the "Gdi32"
function CreateDIBSection which returns an array of bytes as a pointer
argument.
The c# function uses [In][Out] ref IntPtr to represent the array of
bytes returned for the pointer argument passed to CreateDIBSection.
see example:
[DllImport("gdi32.dll")]
static extern IntPtr CreateDIBSection(IntPtr hdc, [In] ref BITMAPINFO
pbmi,
uint iUsage, [In][Out] ref IntPtr ppvBits, IntPtr hSection, uint
dwOffset);
"Stephen Cawood" <cawood@xxxxxxxxxx> wrote in message
news:3y7gg.16349$JX1.2431@xxxxxxxxxxx
I posted this question a few days ago, but it hasn't been resolved so
I'm trying again (with better info).
I'm trying to access a C++ .lib from C#. I can get an int back fine,
the problem I'm having is returning an array of binary data. any
ideas?
thanks in advance...
.lib contains this function:
/-Call create() to create a bitmap of (10*scale) x (*10*scale) bytes
//create() will fill an unsigned char array with 100*scale*scale
bytes
//
//create ID=567, 5 pixels/bit, total image will be 50x50 pixels
//this function will malloc room if image is NULL
//returns -1 if problem, 0 otherwise
int create(int id, int scale, unsigned char *image);
wrapper DLL:
WIN32DLL_API int create_wrapped(int id, int scale, unsigned char
*image)
{
return create(id, scale, image);
}
[DllImport("Wrapper.dll", EntryPoint="create_wrapped")]
public static extern int create_wrapped(int id, int scale, byte[]
image);
byte[] bArray = new byte[500];
create_wrapped(0,5,bArray); //bArray = array of zeros
notes:
I've also tried...
public static extern int create_wrapped(int id, int scale,
[Out][MarshalAs(UnmanagedType.LPArray, SizeConst=500)]byte[] image);
//bArray = array of zeros
public static extern int create_wrapped(int id, int scale,
[MarshalAs(UnmanagedType.LPArray)]byte[] image); //bArray = array of
zeros
public static extern int create_wrapped(int id, int scale,[Out]
IntPtr image); //returns -1 failure
.
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