C++智能感知：表達式必須修改的左值

Question

即時得到這兩個錯誤

1>c:\users\owner\documents\visual studio 2010\projects\monopoly\monopoly\xfileentity.cpp(376): error C3490: 'pDrawMesh' cannot be modified because it is being accessed through a const object 
IntelliSense: expression must be a modifiable lvalue 

我宣佈pDrawMesh在我的課不是在一個函數中使用它。
這裏是我的類

class CXFileEntity 
{ 
     ...... 
LPD3DXMESH pDrawMesh; 
     ..... 
}; 

這裏是我使用的變量

void CXFileEntity::DrawMeshContainer(LPD3DXMESHCONTAINER meshContainerBase, LPD3DXFRAME frameBase) const 
{ 
// Cast to our extended frame type 
D3DXFRAME_EXTENDED *frame = (D3DXFRAME_EXTENDED*)frameBase; 

// Cast to our extended mesh container 
D3DXMESHCONTAINER_EXTENDED *meshContainer = (D3DXMESHCONTAINER_EXTENDED*)meshContainerBase; 

// Set the world transform But only if it is not a skinned mesh. 
// The skinned mesh has the transform built in (the vertices are already transformed into world space) so we set identity 
// Added 24/08/10 
if (meshContainer->pSkinInfo) 
{ 
    D3DXMATRIX mat; 
    D3DXMatrixIdentity(&mat); 
    m_d3dDevice->SetTransform(D3DTS_WORLD, &mat); 
} 
else 
    m_d3dDevice->SetTransform(D3DTS_WORLD, &frame->exCombinedTransformationMatrix); 


// Loop through all the materials in the mesh rendering each subset 
for (unsigned int iMaterial = 0; iMaterial < meshContainer->NumMaterials; iMaterial++) 
{ 
    // use the material in our extended data rather than the one in meshContainer->pMaterials[iMaterial].MatD3D 
    m_d3dDevice->SetMaterial(&meshContainer->exMaterials[iMaterial]); 
    m_d3dDevice->SetTexture(0, meshContainer->exTextures[iMaterial]); 

    // Select the mesh to draw, if there is skin then use the skinned mesh else the normal one 
    pDrawMesh = (meshContainer->pSkinInfo) ? meshContainer->exSkinMesh: meshContainer->MeshData.pMesh; 

    // Finally Call the mesh draw function 
    pDrawMesh->DrawSubset(iMaterial); 
} 
} 

Answer 1

你的成員函數是const限定。除非聲明爲可變，否則不能修改來自const限定成員函數的任何成員變量。

您需要使pDrawMesh變爲可變，從DrawMeshContainer中刪除常規資格，或者找到其他方法來完成您嘗試完成的任何操作。

Answer 2

pDrawMesh確實是this->pDrawMesh。但是由於目前的方法是const方法，因此this是const CXFileEntity*。所以你不能設置成員pDrawMesh。

如果DrawMeshContainer真的應該更改CXFileEntity，請從方法類型中刪除const。如果DrawMeshContainer「有效」保持CXFileEntity不變，並且pDrawMesh成員對於對象的「const」的含義「沒有真正計數」，則可以將成員更改爲mutable。