返回指針的這些函數調用之間有什麼區別？

Question

我正在Qt中解析XML文件，使用QTreeWidget顯示XML的各個部分。我想維護指向每個部分「標題」的指針。

我有這些指針定義：

QTreeWidgetItem* groupExport, 
       groupDesign, 
       groupSheet, 
       groupTitleBlock, 
       groupComponents, 
       groupLibParts, 
       groupLibraries, 
       groupNets; 

我有這些functons：

////////////////////////////////////////////////////////////////////////////// 
/// treeAddRoot 
///--------------------------------------------------------------------------- 
QTreeWidgetItem* window_Main::treeAddRoot(QString name) { 
    QTreeWidgetItem *treeRoot = new QTreeWidgetItem(ui->treeSourceFile); 
    ... 
    return treeRoot; 
} 
QTreeWidgetItem* window_Main::treeAddRoot(QString name, QString description) { 
    QTreeWidgetItem *treeRoot = new QTreeWidgetItem(ui->treeSourceFile); 
    ... 
    return treeRoot; 
} 

////////////////////////////////////////////////////////////////////////////// 
/// treeAddGroup 
///--------------------------------------------------------------------------- 
QTreeWidgetItem* window_Main::treeAddGroup(QTreeWidgetItem *treeParent, QString name) { 
    QTreeWidgetItem *treeChildGroup = new QTreeWidgetItem(treeParent); 
    ... 
    return treeChildGroup; 
} 
QTreeWidgetItem* window_Main::treeAddGroup(QTreeWidgetItem *treeParent, QString name, QString description) { 
    QTreeWidgetItem *treeChildGroup = new QTreeWidgetItem(treeParent); 
    ... 
    return treeChildGroup; 
} 

////////////////////////////////////////////////////////////////////////////// 
/// treeAddChild 
///--------------------------------------------------------------------------- 
void window_Main::treeAddChild(QTreeWidgetItem *treeParent, QString name) { 
    QTreeWidgetItem *treeChild = new QTreeWidgetItem(treeParent); 
    ... 
    treeParent->addChild(treeChild); 
} 
void window_Main::treeAddChild(QTreeWidgetItem *treeParent, QString name, QString description) { 
    QTreeWidgetItem *treeChild = new QTreeWidgetItem(treeParent); 
    ... 
} 

在解析這些是 「臨時」 的使用規定：

QString tempTag, tempValue; 

對於解析代碼，編譯器似乎認爲這是好的：

if (tempTag.contains("export")) { 
    ...    
    groupExport = treeAddRoot(tempTag); 
} 

然而，幾行字後，與此：

error: no match for ‘operator=’ (operand types are ‘QTreeWidgetItem’ and ‘QTreeWidgetItem*’) 
groupDesign = treeAddGroup(groupExport, tempTag); 
      ^

有人能幫助我理解上的差異，爲什麼編譯確定一個和失敗：

if (tempTag.contains("design")) { 
    ... 
    groupDesign = treeAddGroup(groupExport, tempTag); 
} 

與編譯器錯誤在另一 ？

在此先感謝。

Answer 1

定義指針這樣的：

QTreeWidgetItem *groupExport, 
       *groupDesign, 
       *groupSheet, 
       *groupTitleBlock, 
       *groupComponents, 
       *groupLibParts, 
       *groupLibraries, 
       *groupNets;