[英]Marshalling C-style array of LPWSTR to managed string[] using pInvoke
[英]pinvoke: How to free an array of structures containing LPWSTR
為簡化問題,這是我嘗試從.NET類調用的本機方法。
[NativeDll.dll]
頭
typedef struct _ADDRESS {
LPWSTR City;
} ADDRESS, *PADDRESS;
typedef struct _ADDRESS_SET {
ULONG AddressCount;
PADDRESS AddressList;
} ADDRESS_SET, *PADDRESS_SET;
DWORD WINAPI
GetAddressSet(_Outptr_ ADDRESS_SET **AddressSet);
VOID WINAPI
FreeAddressSet(__in ADDRESS_SET *AddressSet);
C ++實現
DWORD WINAPI
GetAddressSet(_Outptr_ ADDRESS_SET **AddressSet) {
HRESULT hr = ERROR_SUCCESS;
const int totalRecords = 2;
LPCWSTR cities[totalRecords] = { L"City 1", L"City 2"};
ADDRESS *addresses = (ADDRESS*)malloc(sizeof(ADDRESS) * totalRecords);
for (int i = 0; i < totalRecords; i++) {
addresses[i].City = (wchar_t*)malloc((wcslen(cities[i]) + 1) * sizeof(wchar_t));
addresses[i].City = (LPWSTR)cities[i];
}
ADDRESS_SET *recordSet = (ADDRESS_SET*)malloc(sizeof(ADDRESS_SET));
recordSet->AddressCount = totalRecords;
recordSet->AddressList = addresses;
*AddressSet = recordSet;
return ERROR_SUCCESS;
}
VOID WINAPI
FreeAddressSet(__in ADDRESS_SET *AddressSet) {
if (AddressSet != NULL) {
if (AddressSet->AddressList != NULL) {
for (int i = 0; i < AddressSet->AddressCount; i++) {
if (AddressSet->AddressList[i].City != NULL) {
free(AddressSet->AddressList[i].City); // <-- This one AVs.
AddressSet->AddressList[i].City = NULL;
}
}
free(AddressSet->AddressList);
AddressSet->AddressList = NULL;
}
free(AddressSet);
AddressSet = NULL;
}
}
當我嘗試從本機代碼調用這些API時,我能夠獲取地址數組。 但是,當我嘗試釋放城市字符串(LPWSTR)時出現AV。
這是我的C#代碼。
[StructLayout(LayoutKind.Sequential)]
internal struct ADDRESS {
internal IntPtr City;
}
[StructLayout(LayoutKind.Sequential)]
internal struct ADDRESS_SET {
// ULONG is 4 bytes.
// ulong in .NET is 8 bytes.
// Hence using uint.
internal UInt32 AddressCount;
internal IntPtr AddressList;
}
internal class NativeMethods {
[DllImport("nativedll.dll", EntryPoint = "GetAddressSet")]
internal static extern UInt32 GetAddressSet(ref IntPtr AddressSet);
[DllImport("nativedll.dll", EntryPoint = "FreeAddressSet")]
internal static extern UInt32 FreeAddressSet([In] IntPtr AddressSet);
}
class Program {
static void Main(string[] args) {
IntPtr pAddressSet = IntPtr.Zero;
UInt32 returnStatus = NativeMethods.GetAddressSet(ref pAddressSet);
if(returnStatus == 0 && pAddressSet != IntPtr.Zero) {
ADDRESS_SET addressSet = Marshal.PtrToStructure<ADDRESS_SET>(pAddressSet);
UInt32 addressCount = addressSet.AddressCount;
IntPtr addressList = addressSet.AddressList;
if (addressCount != 0 && addressList != IntPtr.Zero) {
for (int i = 0; i < addressCount; i++) {
ADDRESS address = Marshal.PtrToStructure<ADDRESS>(addressList);
addressList += Marshal.SizeOf(typeof(ADDRESS));
Console.WriteLine($"City: {Marshal.PtrToStringUni(address.City)}");
}
}
}
NativeMethods.FreeAddressSet(pAddressSet); // <-- Call fails to free the City string.
}
}
在此示例中,我將Address結構內的City字段設置為IntPtr。 我也嘗試將City字段設置為[MarshalAs(UnmanagedType.LPWStr)]字符串,但無法成功釋放。 我不確定.NET代碼中有什么錯誤。
問題出在您的C ++代碼中。 您為該字符串分配內存,但是永遠不要寫入該內存。
addresses[i].City = (wchar_t*)malloc((wcslen(cities[i]) + 1) * sizeof(wchar_t));
addresses[i].City = (LPWSTR)cities[i];
如果啟用了編譯器提示和警告,編譯器將告訴您第一行中分配的值將永遠不會使用。
第二行是錯誤的。 相反,您必須使用wcscpy_s()復制字符串內容。 現在,FreeAddressSet()函數可以使用malloc()返回的實際指針值正確調用free()。
聲明:本站的技術帖子網頁,遵循CC BY-SA 4.0協議,如果您需要轉載,請注明本站網址或者原文地址。任何問題請咨詢:yoyou2525@163.com.