编辑：我在下面发布了一个更好的实现。我把它留在这里，所以回答是有意义的。
我已经对在Delphi中编写DLL的正确方法进行了大量搜索，并且能够从C＃调用它，传递和返回字符串。许多信息不完整或不正确。经过多次试验和错误，我找到了解决方案。
这是使用Delphi 2007和VS 2010编译的。我怀疑它在其他版本中也可以正常工作。
这是Delphi代码。请记住在项目中包含版本信息。
library DelphiLibrary;
uses SysUtils;
// Compiled using Delphi 2007.
// NOTE: If your project doesn't have version information included, you may
// receive the error "The "ResolveManifestFiles" task failed unexpectedly"
// when compiling the C# application.
{$R *.res}
// Example function takes an input integer and input string, and returns
// inputInt + 1, and inputString + ' ' + IntToStr(outputInt) as output
// parameters. If successful, the return result is nil (null), otherwise it is
// the exception message string.
// NOTE: I've posted a better version of this below. You should use that instead.
function DelphiFunction(inputInt : integer; inputString : PAnsiChar;
out outputInt : integer; out outputString : PAnsiChar)
: PAnsiChar; stdcall; export;
var s : string;
begin
outputInt := 0;
outputString := nil;
try
outputInt := inputInt + 1;
s := inputString + ' ' + IntToStr(outputInt);
outputString := PAnsiChar(s);
Result := nil;
except
on e : exception do Result := PAnsiChar(e.Message);
end;
end;
// I would have thought having "export" at the end of the function declartion
// (above) would have been enough to export the function, but I couldn't get it
// to work without this line also.
exports DelphiFunction;
begin
end.
这是C＃代码：
using System;
using System.Runtime.InteropServices;
namespace CsharpApp
{
class Program
{
// I added DelphiLibrary.dll to my project (NOT in References, but
// "Add existing file"). In Properties for the dll, I set "BuildAction"
// to None, and "Copy to Output Directory" to "Copy always".
// Make sure your Delphi dll has version information included.
[DllImport("DelphiLibrary.dll",
CallingConvention = CallingConvention.StdCall,
CharSet = CharSet.Ansi)]
public static extern
string DelphiFunction(int inputInt, string inputString,
out int outputInt, out string outputString);
static void Main(string[] args)
{
int inputInt = 1;
string inputString = "This is a test";
int outputInt;
string outputString;
// NOTE: I've posted a better version of this below. You should use that instead.
Console.WriteLine("inputInt = {0}, intputString = \"{1}\"",
inputInt, inputString);
var errorString = DelphiFunction(inputInt, inputString,
out outputInt, out outputString);
if (errorString != null)
Console.WriteLine("Error = \"{0}\"", errorString);
else
Console.WriteLine("outputInt = {0}, outputString = \"{1}\"",
outputInt, outputString);
Console.Write("Press Enter:");
Console.ReadLine();
}
}
}
我希望这些信息可以帮助别人不必像我一样把头发拉出来。
答案 0 :(得分：25)
根据对帖子的回复，我创建了一个新的示例，它为返回的字符串使用字符串缓冲区，而不是仅返回PAnsiChars。
Delphi DLL源：
library DelphiLibrary;
uses SysUtils;
// Compiled using Delphi 2007.
// NOTE: If your project doesn't have version information included, you may
// receive the error "The "ResolveManifestFiles" task failed unexpectedly"
// when compiling the C# application.
{$R *.res}
// A note on returing strings. I had originally written this so that the
// output string was just a PAnsiChar. But several people pointed out that
// since Delphi strings are reference-counted, this was a bad idea since the
// memory for the string could get overwritten before it was used.
//
// Because of this, I re-wrote the example so that you have to pass a buffer for
// the result strings. I saw some examples of how to do this, where they
// returned the actual string length also. This isn't necessary, because the
// string is null-terminated, and in fact the examples themselves never used the
// returned string length.
// Example function takes an input integer and input string, and returns
// inputInt + 1, and inputString + ' ' + IntToStr(outputInt). If successful,
// the return result is true, otherwise errorMsgBuffer contains the the
// exception message string.
function DelphiFunction(inputInt : integer;
inputString : PAnsiChar;
out outputInt : integer;
outputStringBufferSize : integer;
var outputStringBuffer : PAnsiChar;
errorMsgBufferSize : integer;
var errorMsgBuffer : PAnsiChar)
: WordBool; stdcall; export;
var s : string;
begin
outputInt := 0;
try
outputInt := inputInt + 1;
s := inputString + ' ' + IntToStr(outputInt);
StrLCopy(outputStringBuffer, PAnsiChar(s), outputStringBufferSize-1);
errorMsgBuffer[0] := #0;
Result := true;
except
on e : exception do
begin
StrLCopy(errorMsgBuffer, PAnsiChar(e.Message), errorMsgBufferSize-1);
Result := false;
end;
end;
end;
// I would have thought having "export" at the end of the function declartion
// (above) would have been enough to export the function, but I couldn't get it
// to work without this line also.
exports DelphiFunction;
begin
end.
C＃代码：
using System;
using System.Runtime.InteropServices;
namespace CsharpApp
{
class Program
{
// I added DelphiLibrary.dll to my project (NOT in References, but
// "Add existing file"). In Properties for the dll, I set "BuildAction"
// to None, and "Copy to Output Directory" to "Copy always".
// Make sure your Delphi dll has version information included.
[DllImport("DelphiLibrary.dll",
CallingConvention = CallingConvention.StdCall,
CharSet = CharSet.Ansi)]
public static extern bool
DelphiFunction(int inputInt, string inputString,
out int outputInt,
int outputStringBufferSize, ref string outputStringBuffer,
int errorMsgBufferSize, ref string errorMsgBuffer);
static void Main(string[] args)
{
int inputInt = 1;
string inputString = "This is a test";
int outputInt;
const int stringBufferSize = 1024;
var outputStringBuffer = new String('\x00', stringBufferSize);
var errorMsgBuffer = new String('\x00', stringBufferSize);
if (!DelphiFunction(inputInt, inputString,
out outputInt,
stringBufferSize, ref outputStringBuffer,
stringBufferSize, ref errorMsgBuffer))
Console.WriteLine("Error = \"{0}\"", errorMsgBuffer);
else
Console.WriteLine("outputInt = {0}, outputString = \"{1}\"",
outputInt, outputStringBuffer);
Console.Write("Press Enter:");
Console.ReadLine();
}
}
}
这是一个额外的类，它显示了如何动态加载DLL（对不起，排长队）：
using System;
using System.Runtime.InteropServices;
namespace CsharpApp
{
static class DynamicLinking
{
[DllImport("kernel32.dll", EntryPoint = "LoadLibrary")]
static extern int LoadLibrary([MarshalAs(UnmanagedType.LPStr)] string lpLibFileName);
[DllImport("kernel32.dll", EntryPoint = "GetProcAddress")]
static extern IntPtr GetProcAddress(int hModule, [MarshalAs(UnmanagedType.LPStr)] string lpProcName);
[DllImport("kernel32.dll", EntryPoint = "FreeLibrary")]
static extern bool FreeLibrary(int hModule);
[UnmanagedFunctionPointer(CallingConvention.StdCall, CharSet = CharSet.Ansi)]
delegate bool DelphiFunction(int inputInt, string inputString,
out int outputInt,
int outputStringBufferSize, ref string outputStringBuffer,
int errorMsgBufferSize, ref string errorMsgBuffer);
public static void CallDelphiFunction(int inputInt, string inputString,
out int outputInt, out string outputString)
{
const string dllName = "DelphiLib.dll";
const string functionName = "DelphiFunction";
int libHandle = LoadLibrary(dllName);
if (libHandle == 0)
throw new Exception(string.Format("Could not load library \"{0}\"", dllName));
try
{
var delphiFunctionAddress = GetProcAddress(libHandle, functionName);
if (delphiFunctionAddress == IntPtr.Zero)
throw new Exception(string.Format("Can't find function \"{0}\" in library \"{1}\"", functionName, dllName));
var delphiFunction = (DelphiFunction)Marshal.GetDelegateForFunctionPointer(delphiFunctionAddress, typeof(DelphiFunction));
const int stringBufferSize = 1024;
var outputStringBuffer = new String('\x00', stringBufferSize);
var errorMsgBuffer = new String('\x00', stringBufferSize);
if (!delphiFunction(inputInt, inputString, out outputInt,
stringBufferSize, ref outputStringBuffer,
stringBufferSize, ref errorMsgBuffer))
throw new Exception(errorMsgBuffer);
outputString = outputStringBuffer;
}
finally
{
FreeLibrary(libHandle);
}
}
}
}
-Dan
答案 1 :(得分：5)
正如Jeroen Pluimers在评论中所说，你应该注意Delphi字符串是引用计数的。
IMO，在您应该在异构环境中返回字符串的情况下，您应该要求调用者为结果提供缓冲区，并且该函数应该填充该缓冲区。这样，调用者负责创建缓冲区并在完成缓冲区时进行处理。如果您看一下Win32 API函数，当他们需要将字符串返回给调用者时，您会看到他们也这样做。
为此，您可以使用PChar（PAnsiChar或PWideChar）作为函数参数的类型，但您也应该要求调用者提供缓冲区的大小。请在下面的链接中查看我的答案，获取示例源代码：
Exchanging strings (PChar) between a Freepascal compiled DLL and a Delphi compiled EXE
问题是关于在FreePascal和Delphi之间交换字符串，但是这个想法和答案也适用于你的情况。
答案 2 :(得分：2)
在Delphi 2009中，如果您明确将变量s键入为AnsiString，则代码可以更好地运行：
var s : Ansistring;
在通话后给出C＃的预期结果：
outputInt = 2, outputString = "This is a test 2"
而不是
outputInt = 2, outputString = "T"
答案 3 :(得分：0)
使用String检索字符串更容易：
function DelphiFunction(inputString : PAnsiChar;
var outputStringBuffer : PString;
var errorMsgBuffer : PString)
: WordBool; stdcall; export;
var
s : string;
begin
try
s := inputString;
outputStringBuffer:=PString(AnsiString(s));
Result := true;
except
on e : exception do
begin
s:= 'error';
errorMsgBuffer:=PString(AnsiString(e.Message));
Result := false;
end;
end;
end;
在c＃中然后：
const int stringBufferSize = 1024;
var str = new IntPtr(stringBufferSize);
string loginResult = Marshal.PtrToStringAnsi(str);