小编kre*_*ves的帖子

我正在尝试编写一个简单的B +树实现(非常早期阶段).我有一个带有一些功能的虚拟课程.毋庸置疑,我对这些策略很陌生,遇到各种各样的问题.

我正在尝试在BTree类中创建一个根节点.根节点将是BBranch,它应该继承自BNode？我收到了错误

btree.cpp: In constructor âBTree::BTree()â:
btree.cpp:25: error: cannot declare variable ârootâ to be of abstract type âBBranchâ
btree.cpp:12: note:   because the following virtual functions are pure within âBBranchâ:
btree.cpp:9: note:      virtual void BNode::del(int)
btree.cpp: In member function âvoid BTree::ins(int)â:
btree.cpp:44: error: ârootâ was not declared in this scope

代码是这样的

using namespace std;

class BNode {
  public:
    int key [10];
    int pointer [11];
    virtual void ins( int num ) =0;
    virtual void del( int num ) =0;
};

class …

我在Windows上使用由ActiveState构建的Perl v5.12.3.DBD :: Oracle版本1.27.DBI版本1.616.我正按照这个特定的顺序选择下面的数据,并希望以相同的顺序检索结果数据.下面是代码示例和一些示例.

SQL Snippet(下面$ report_sql的内容)

select student_number, lastfirst, counselor, 
   a.dateenrolled as "Date Enrolled 1", a.dateleft as "Date Left 1", a.termid as "Term ID 1", a.course_number as "Course Number 1", 
   a.expression as "Expression 1", b.dateenrolled as "Date Enrolled 2", b.dateleft as "Date Left 2", 
   b.termid as "Term ID 2", b.course_number as "Course Number 2", b.expression as "Expression 2"

Perl代码段

## run the resulting query
my $report_result = $dbh->prepare( $report_sql );
$report_result->execute();   
while( my $report_row = $report_result->fetchrow_hashref())
        {
            print Dumper(\$report_row); …