Win32::API DLL Point 变量传递问题

jjboy110

Hi All,
我遇到一个Perl调用外部DLL函数传递指针变量的问题。
我查阅到Win32::API 之中，关于调用dll 之中有指针变量的部分，

1. P: value is a pointer (to a string, structure, etc...) padding out the buffer string is required, buffer overflow detection is performed. Pack and unpack the data yourself. If P is a return type, only null terminated strings or NULL pointer are supported. If P is an in type, NULL is integer 0. undef, "0", and ""+0 are not integer 0, "0"+0 is integer 0.
   
2. It is suggested to not use P as a return type and instead use N and read the memory yourself, and free the pointer if applicable. This pointer is effectively undefined after the C function returns control to Perl. The C function may not hold onto it after the C function returns control. There are exceptions where the pointer will remain valid after the C function returns control, but tread at your own risk, and at your knowledge of Perl interpreter's C internals.

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这段描述的内容我不太理解，我尝试使用以下代码将指针传递进入，Card.dll为一个外部DLL，但是无法从这个变量获得返回结果，

1. [code]my $cs = new Win32::API('Card', 'Card_Set', 'P', 'I');
   
2. my $b = 1;
   
3. my $err = $cs->Call($b);
   
4. print $b;

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[/code]
然后我查阅到有可能是C++的指针类型与perl指针有差，perl传递的地址与进入dll以后的地址不一致，所以我无法拿到需要的结果，从以上关于指针参数描述的要求，他们建议我们自己查找内存得到结果，不知道关于这一块，大家是否有类似的经验可以帮助？我发现关于Perl的技术文章随着时间的逝去，很多服务器上的文章都在消逝，有些文章已经查不到了，虽然很有用。
谢谢各位。