什么可能导致“MyType *pType”在返回时从有效参数变为 null？
考虑这个方法：
result MyClass::getBMPText(Osp::Graphics::Bitmap *pBMP, Osp::Base::String &outtext, const int index) const {
//Do stuff
AppLog("3 Returning %S, 0x%X", outtext.GetPointer(), (int)pBMP);
return E_SUCCESS;
}
我这样称呼它：
String itemstr;
Bitmap *pBMP = null;
for (int i = 0; i < ItemCount(); ++i) {
getBMPText(pBMP, itemstr, i);
AppLog("got %d : %S 0x%X", i, itemstr.GetPointer(), (int)pBMP);
}
现在看一下日志：
5537.642,INFO,P35,T00,A190,FileMan::getBMPText (401)> 3 返回图像，0xB96E2140 5537.643,INFO,P35,T00,A190,FileMan::Update1p2List (130) >得到 0：图像 0x0
重复我的问题/观察：该函数将其返回值记录为有意义且与刚刚设置的相关。然而，客户端会返回与它发送的相同的空引用。
Consider this method:
result MyClass::getBMPText(Osp::Graphics::Bitmap *pBMP, Osp::Base::String &outtext, const int index) const {
//Do stuff
AppLog("3 Returning %S, 0x%X", outtext.GetPointer(), (int)pBMP);
return E_SUCCESS;
}
I call it like this:
String itemstr;
Bitmap *pBMP = null;
for (int i = 0; i < ItemCount(); ++i) {
getBMPText(pBMP, itemstr, i);
AppLog("got %d : %S 0x%X", i, itemstr.GetPointer(), (int)pBMP);
}
Now take a look at the log:
5537.642,INFO,P35,T00,A190,FileMan::getBMPText (401) > 3 Returning Images, 0xB96E2140
5537.643,INFO,P35,T00,A190,FileMan::Update1p2List (130) > got 0 : Images 0x0
To repeat my question/observation: The function logs its return value as meaningful and relevent having just set it. The client however gets back the same null reference it sent in.
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评论（3）
您按值传递指针，因此原始指针永远不会改变。将函数签名更改为 Osp::Graphics::Bitmap * & pBMP 通过引用传递指针。
You're passing the pointer by value, so the original pointer never gets changed. Change the function signature to
Osp::Graphics::Bitmap * & pBMPto pass the pointer by reference.如果您想更改原始指针，则必须将其作为指针或引用传递。例如。函数
getBMPTest将被声明为并被调用，
如果您更喜欢指针，您可以这样做：
If you'd like to change the original pointer, you'll have to pass it as a pointer or as a reference. For example. the function
getBMPTestwould be declared asand called like
If you prefer pointers, you can do it like this instead:
这是因为您没有在函数内设置
*pBMP（您设置了pBMP，指针类型）。更改指针本身不会影响其目标。同样，使用
index时，您是按值传递的，因此不会产生任何结果。This is because you're not setting
*pBMPinside the function (you setpBMP, the pointer type). Changing the pointer itself won't affect its target.Likewise, with
index, you're passing by value, so nothing comes out.