Delphi调用WinC编写的DLL问题?(100分)

C语言Dll文件，文件名cdll.dll<br>extern "C" __declspec(dllexport) char * GetMemberSum(LPTSTR vMemberName);<br>extern "C" __declspec(dllexport) char * GetMemberSum(LPTSTR vMemberName)<br>{ <br>return vMemberName;<br>} <br><br>Delphi主程序,运行下面程序后，返回结果是对的，但是马上就报错，什么原因，请指点！<br>unit testMain;<br>interface<br>uses<br>&nbsp; Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,<br>&nbsp; StdCtrls;<br>type<br>&nbsp; TForm1 = class(TForm)<br>&nbsp; &nbsp; Button1: TButton;<br>&nbsp; &nbsp; procedure Button1Click(Sender: TObject);<br>&nbsp; private<br>&nbsp; &nbsp; { Private declarations }<br>&nbsp; public<br>&nbsp; &nbsp; { Public declarations }<br>&nbsp; end;<br>var<br>&nbsp; Form1: TForm1;<br>&nbsp; function GetMemberSum(vMemberName: String) : PChar; stdcall;<br>implementation<br>&nbsp; function GetMemberSum; external 'cdll.DLL' name 'GetMemberSum';<br>{$R *.DFM}<br>procedure TForm1.Button1Click(Sender: TObject);<br>var<br>&nbsp; sChar;<br>begin<br>&nbsp; s:=GetMemberSum('TestStr');<br>&nbsp; showmessage(s );<br>end;<br>end.

函数声明改为： GetMemberSum(vMemberName: PChar) : PChar; stdcall;<br>

Delphi做了如下更正，返回的结果是正确的，可是出现错误提示'access violation at<br>0x0012f6fd: write of address 0x00000000'这样的错误<br>

&nbsp;FreeMem(p);错误，你不能释放DLl中的内存。<br>

我跟踪看了一下，这是不是Delphi调用C的DLL的一个Bug呀，我按下面的写法就可以了<br>&nbsp; GetMem(p,1024);<br>&nbsp; strPCopy(p,'N020010320010');<br>&nbsp; s:=GetMemberSum(p);<br>&nbsp; asm<br>&nbsp; &nbsp; pop eax;<br>&nbsp; end;<br>&nbsp; showmessage(s);<br>&nbsp; FreeMem(p);<br>在我跟踪时发现调用GetMemberSum(p)之后，stack居然不平衡了，我用了一句Pop eax 是保<br>证stack的平衡的，在我这里测试通过！<br>

O，是调用约定搞错了，你用 extern "C" 声明的，在Delphi 中声明要用cdecl 将<br>function GetMemberSum(vMemberName: PChar) : PChar; stdcall;<br>而为<br>function GetMemberSum(vMemberName: PChar) : PChar; cdecl;就行了，现在stack就平<br>衡了！：)！<br><br>

qiya水平可真高，在向你请教一下<br>stdcall;<br>cdecl;<br>的区别，还望告之，谢谢！<br><br>

&gt;&gt;mrzj<br>不要笑话我了，大家共同学习<br>stdcall 和 cdecl 的区别在于调用函数时压入stack的参数是由谁来移除，对于stdcall<br>它是在被调用的函数中移去参数，保证stack的平衡,而cdecl则由调用者移去，对于这种<br>指示符主要用在函数中有不固定参数的情况下，像printf!<br>详细的说明Delphi help 中有的！