On Monday, 26 December 2022 at 16:44:37 UTC, Ali Çehreli wrote:
> In any case, I have a presentation "Exposing a D Library to Python Through a C API", which touches up on these topics:
I found the problem I was running into before. Why does returning a struct, or sending a D string via an out parameter, work here, but simply returning a D string does not?
D DLL
static struct DString {
size_t length;
immutable(char)* ptr;
this(string str) {
length = str.length;
ptr = str.ptr;
}
void opAssign(string str) {
length = str.length;
ptr = str.ptr;
}
}
static this() {
cache = null; // DLL memory error if not initialized here
}
string[string] cache;
export string MyDLL_testStringReturn() {
string s = "hello";
cache.require(s);
writefln("[D] pass: %s", s);
return s;
}
export DString MyDLL_testStringReturnStruct() {
string s = "hello";
cache.require(s);
auto dstr = DString(s);
writefln("[D] pass: %s", dstr);
return dstr;
}
export void MyDLL_testStringOut(out string str) {
string s = "hello";
cache.require(s);
str = s;
writefln("[D] pass: %s", str);
}
C# Main
[StructLayout(LayoutKind.Sequential, Size=16, Pack=1)]
public struct DString {
public ulong length;
public IntPtr ptr;
public string str {
get {
byte[] b = new byte[length];
for (int i = 0; i < (int)length; i++) {
b[i] = Marshal.ReadByte(ptr, i);
}
return Encoding.UTF8.GetString(b);
}
}
}
[DllImport("mydll.dll")]
private static extern DString MyDLL_testStringReturn();
[DllImport("mydll.dll")]
private static extern DString MyDLL_testStringReturnStruct();
[DllImport("mydll.dll")]
private static extern void MyDLL_testStringOut(out DString dd);
public static void testString() {
System.Console.WriteLine("Test [RETURN D string]");
DString d1 = MyDLL_testStringReturn();
System.Console.WriteLine("ok");
System.Console.WriteLine("len: {0}", d1.length);
System.Console.WriteLine("d1: {0}", d1.str);
System.Console.WriteLine("Test [RETURN D struct]");
DString d2 = MyDLL_testStringReturnStruct();
System.Console.WriteLine("ok");
System.Console.WriteLine("len: {0}", d2.length);
System.Console.WriteLine("d2: {0}", d2.str);
System.Console.WriteLine("Test [OUT D string]");
DString d3;
MyDLL_testStringOut(out d3);
System.Console.WriteLine("ok");
System.Console.WriteLine("len: {0}", d3.length);
System.Console.WriteLine("d3: {0}", d3.str);
}
Output
Test [RETURN D string]
[D] pass: hello
ok
len: 0 !! Should be 5!
d1: !! Should be hello!
Test [RETURN D struct]
[D] pass: DString(5, 7FFA497BCDD0)
ok
len: 5
d2: hello
Test [OUT D string]
[D] pass: hello
ok
len: 5
d3: hello
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