[DCC Error] JwaStrSafe.pas(2277): E2010 Incompatible types: 'PSTRSAFE_LPWSTR' and 'PSTRSAFE_LPTSTR'
以下是来自JwaStrSafe.pas(来自Jedi Api)的代码的相关部分,我正在使用UNICODE定义的符号进行编译：
type
STRSAFE_LPWSTR = PWIDECHAR;
PSTRSAFE_LPWSTR = ^STRSAFE_LPWSTR;
{$IFDEF UNICODE}
STRSAFE_LPTSTR = STRSAFE_LPWSTR;
PSTRSAFE_LPTSTR = ^STRSAFE_LPTSTR;
{$ELSE}
...
{$ENDIF}
...
//function declaration
function StringCchCopyExW(
{__out_ecount(cchDest)}pszDest : STRSAFE_LPWSTR;
{__in}cchDest : size_t;
{__in}const pszSrc : STRSAFE_LPCWSTR;
{__deref_opt_out_ecount(pcchRemaining^)}ppszDestEnd : PSTRSAFE_LPWSTR;
{__out_opt}pcchRemaining : PSize_t;
{__in}dwFlags : Cardinal) : HRESULT; stdcall; forward; external;
...
//var passed to function
ppszDestEnd : PSTRSAFE_LPTSTR;
...
{$IFDEF UNICODE}
result := StringCchCopyExW(pszDest,cchDest,pszSrc,ppszDestEnd,pcchRemaining,dwFlags);
{$ELSE}
result := StringCchCopyExA(pszDest,dwFlags);
{$ENDIF}
我在参数ppszDestEnd上调用StringCchCopyExW时出错.
查看类型定义我明白PSTRSAFE_LPTSTR是STRSAFE_LPTSTR的指针类型,它只是STRSAFE_LPWSTR的别名,为什么PSTRSAFE_LPTSTR和PSTRSAFE_LPWSTR不兼容？
解
感谢大卫的解释我取代了
PSTRSAFE_LPTSTR = ^STRSAFE_LPTSTR;
同
PSTRSAFE_LPTSTR = PSTRSAFE_LPWSTR;
谢谢
解决方法
program PointerTypeCompatibility;
{$APPTYPE CONSOLE}
type
A = Integer;
B = Integer;
var
ptA: ^A;
ptB: ^B;
begin
ptA := ptB;
end.
这也产生了E2010.但是,如果启用type-checked pointers选项,则代码将成功编译.实际上,该编译器选项的文档指出：
In the {$T-} state,distinct pointer types other than Pointer are incompatible (even if they are pointers to the same type). In the {$T+} state,pointers to the same type are compatible.
感谢Ken White为我指出了有用的帮助主题Type Compatibility and Identity.相关的摘录是T1和T2类型在以下情况下是分配兼容的：
T1 and T2 are compatible pointer types.
文档还指出类型是类型兼容的,如果：
Both types are (typed) pointers to the same type and the {$T+} compiler directive is in effect.
所以这记录了观察到的行为并引导我到这个例子：
program PointerTypeCompatibilityTake2;
{$APPTYPE CONSOLE}
{$TYPEDADDRESS OFF}
var
P1,P2: ^Integer;
P3: ^Integer;
begin
P1 := P2;//compiles
P1 := P3;//E2008 Incompatible types
end.
所以,总结一下：
>当禁用类型检查指针时,如果指针属于同一类型,则指针是赋值兼容的.
>当启用类型检查指针时,如果指针指向相同类型,则指针是赋值兼容的.
我不得不承认对类型检查指针设置背后的历史和推理一无所知,所以我无法解释为什么编译器就是这样的.