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