如何通过Dll传递string类型的值。。。

[dead_lee]

希望用Pchar实现，不过我写的几个测试程序出现错误

[sunon]

我也有这样的问题.

[dead_lee]

我想写一个dll供其他程序调用，其中需要传递字符串出来，由于pascal对于string的处理
方式，我想传递出一个pchar出来，程序如下
dll中的函数
function StringTest(out Pstr: Pchar): integer;
var
Str: string;
Chars: array[0..255] of char;
i: integer;
begin
for i:=1 to 255 do
begin
Chars[i] := #0;
end;

Str := 'leetest'+#0;
for i:=0 to Length(Str) do
begin
Chars[i] := Str[i];
end;

Pstr := @Chars;
end;
宿主程序部分:
procedure TForm1.Button1Click(Sender: TObject);
var
Msg: string;
PStr: Pchar;
begin
PStr := nil;
StringTest(PStr);
Msg := PStr;
ShowMessage(Msg);
end;
程序出现非法访问错误,经察看帮助得知是因为不能将函数中的局部变量的地址返回所至
帮助信息如下
A common error when working with PChars is to store in a data structure, or
return as a value, a local variable. When your routine ends, the PChar will
disappear because it is simply a pointer to memory, and is not a reference
counted copy of the string. For example:

function title(n: Integer): PChar;
var
s: string;
begin
s := Format('title - %d', [n]);
Result := PChar(s); // DON'T DO THIS
end;

This example returns a pointer to string data that is freed when the
title function returns.
现在想知道到底如何是正确的做法.

[newyj]

Str := 'leetest'+#0;
for i:=1to Length(Str) do
begin
Chars[i-1] := Str[i];
end;

[newyj]

getmem(PStr,256);
StringTest(PStr);

[dead_lee]

我修改程序成这个样子...
dll的函数
function StringTest(out Pstr: Pchar): integer;
var
Str: string;
i: integer;
begin
Str := 'leetest';
StrPCopy(Pstr, Str);
end;
宿主程序部分
procedure TForm1.Button1Click(Sender: TObject);
var
Msg: string;
PStr: Pchar;
begin
getmem(PStr, 256);
StringTest(PStr);
Msg := PStr;
ShowMessage(Msg);
// FreeMem(Pstr, 256);
end;
现在的依然会有内存错误,不过变成了第1,3,5次点击会出错,第2,4,6次能显示数据,但是
只显示了'est',请继续指教,谢谢...
另外,如果加上FreeMem的那一句,会出'不正确的指针操作'这样的错误.