錯誤C2228：左 '.Alloc' 必須具有類/結構/聯合

Question

我有一個SDK（千兆以太網C++），它定義了這樣的一類：

class PV_BUFFER_API PvBuffer 
{ 

public: 

PvBuffer(); 
virtual ~PvBuffer(); 
PvPayloadType GetPayloadType() const; 
#ifndef PV_NODEPRECATED 
PvResult Alloc(PvUInt32 aSizeX, PvUInt32 aSizeY, PvPixelType aPixelType); 
}; 

的SDK的文件說：

PvResult PvBuffer::Alloc (PvUInt32 aSizeX, 
PvUInt32 aSizeY, 
PvPixelType aPixelType 
)  

Allocates memory for this PvBuffer. 

Parameters: 
[in] aSizeX The width of the image, in pixels. See GetWidth. 
[in] aSizeY The height of the image, in pixels. See GetHeight. 
[in] aPixelType The GEV pixel type from which the pixel depth is extracted. For  
supported pixel types, see PvPixelType.h. 

Returns: 
Includes: 
PvResult::Code::OK 
PvResult::Code::NOT_ENOUGH_MEMORY 

我想使用的功能的Alloc（請參閱類的最後一個函數）。所以我寫這樣的程序：

PvBuffer *lBuffer; //Class name is PvBuffer 
PvResult lResult= lBuffer.Alloc(1224, 1029, PVPIXELMONO); 

但它給錯誤，其中之一是：

error C2228: left of '.Alloc' must have class/struct/union 

是語法是否正確？爲什麼它是要求類？什麼是正確的方法是什麼？

Answer 1

PvBuffer *lBuffer; //Class name is PvBuffer 
PvResult lResult= lBuffer.Alloc(1224, 1029, PVPIXELMONO); 

撇開這調用未定義行爲，爲lBuffer沒有初始化，你想：

PvResult lResult= lBuffer->Alloc(1224, 1029, PVPIXELMONO); 

因爲lBuffer是一個指針。

Answer 2

lBuffer是PvBuffer*，你需要創建和尊重：

lBuffer = new PvBuffer() 
lBuffer->Alloc(....);