How to: Load Unmanaged Resources into a Byte Array
This topic discusses several ways to load unmanaged resources into a Byte array.
If you know the size of your unmanaged resource, you can preallocate a CLR array and then load the resource into the array using a pointer to the array block of the CLR array.
// load_unmanaged_resources_into_Byte_array.cpp
// compile with: /clr
using namespace System;
void unmanaged_func( unsigned char * p ) {
for ( int i = 0; i < 10; i++ )
p[ i ] = i;
}
public ref class A {
public:
void func() {
array<Byte> ^b = gcnew array<Byte>(10);
pin_ptr<Byte> p = &b[ 0 ];
Byte * np = p;
unmanaged_func( np ); // pass pointer to the block of CLR array.
for ( int i = 0; i < 10; i++ )
Console::Write( b[ i ] );
Console::WriteLine();
}
};
int main() {
A^ g = gcnew A;
g->func();
}
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This sample shows how to copy data from an unmanaged memory block to a managed array.
// load_unmanaged_resources_into_Byte_array_2.cpp
// compile with: /clr
using namespace System;
using namespace System::Runtime::InteropServices;
#include <string.h>
int main() {
char buf[] = "Native String";
int len = strlen(buf);
array<Byte> ^byteArray = gcnew array<Byte>(len + 2);
// convert any native pointer to IntPtr by doing C-Style cast
Marshal::Copy( (IntPtr)buf, byteArray, 0, len );
}
Performance concerns
Neither of these examples provide optimal bytes / performance. The Marshal class in general, while helpful, has poor execution performance. Pinning the array and copying the content is better, but you should copy 8 bytes / 64 bits / a long at a time, then if the array length is not aligned, copy the potentially remaining 1 to 7 bytes, for faster performance (8 bytes is one CPU register / 1 operation).
- 8/23/2011
- David Burg
