int RM_FileScan::NextRec(RM_Record &rec, RID &rid) {
if (isclose) {
//cout << "[RM_FileScan]GetNextRec error: This filescan has been closed!" << endl;
return 2;
}
//NULL1:当comparevalue为NULL且op为大小于中的一个时为用假，返回为空
if(op <= GE && op >= LT && comparevalue == NULL) return 1;
bool get_flag = false;
int index;
Bytes head = (Bytes)filehandle->bpm->getPage(currentRid->GetFileid(), currentRid->GetPageid(), index);
Bits* slots = new Bits(head, filehandle->GetPnum());
Bytes record_head;
int current_slotid = currentRid->GetSlotid();
int current_pageid = currentRid->GetPageid();
int offset = PAGE_HEAD_BYTE;
while (!get_flag) {
// cout << "fuck1" << endl;
while ( current_slotid < filehandle->GetPnum() && slots->bit_get(current_slotid) == false) {
current_slotid++;
}
// cout << "fuck2" << endl;
if (current_slotid == filehandle->GetPnum()) { //该页记录已全部遍历
current_pageid++;
current_slotid = 0;
if (current_pageid == filehandle->GetPsum()) { //说明该文件下所有页的所有记录都已遍历过.此时返回0表示已遍历完
currentRid->SetPageid(current_pageid);
currentRid->SetSlotid(current_slotid);
return 1;
}
head = (Bytes)filehandle->bpm->getPage(currentRid->GetFileid(), current_pageid, index);
slots->setData(head);
offset = PAGE_HEAD_BYTE;
} else { //得到一个记录
// cout << "fuck3" << endl;
offset = PAGE_HEAD_BYTE;
offset = offset + filehandle->GetRsize() * current_slotid;
record_head = head + offset;
int nullbits_offset = RECORD_NULLBITS_OFFSET_BYTE;
Bits* nullbits = new Bits(record_head + nullbits_offset, attrcol+1); //获取相应记录的null位图(一定长度)
//NULL2.1:左边NULL且需要判等（不等），则直接通过null位图来判别
//NULL2.2:左边NULL且op为大小于，直接返回true
// cout << "fuck3.1" << endl;
if(nullbits->bit_get(attrcol) == 0) {//左边为NULL
if(op == NO) {
get_flag = true;
}
if(op <= GE && op >= LT) { //为理解方便写出来，实际没什么用
get_flag = false;
}
if(op == EQ) {
get_flag = (comparevalue == NULL);
}
if(op == NE) {
get_flag = !(comparevalue == NULL);
}
} else /*if (comparevalue != 0)*/{//其他情况，进行相应比较
// cout << "fuck3.2" << endl;
char* value_head = record_head + attroffset;
// enum AttrType{INTEGER,FLOAT,STRING};
// enum CompOp{EQ,LT,GT,LE,GE,NE,NO};
// cout << "11" << endl;
const char* cmp1 = value_head;
const char* cmp2 = (char*)comparevalue;
const CompOp cmpop = op;
const AttrType cmptype = type;
// cout << "22" << endl;
if (comparevalue != 0 || op == NO){
// cout << "33" << endl;
get_flag = compareData(cmp1, cmpop, cmp2, cmptype);
}
else
get_flag = false;
}
// cout << "fuck4" << endl;
if (get_flag) {
rec.SetSize(filehandle->GetRsize());
// cout << "get_data: " << &get_data << " " << "head: " << &record_head << endl;
rec.SetData(record_head);
} else {
current_slotid++;
}
// cout << "fuck5" << endl;
}
}
//设置RID
rid.SetFileid(-1);
rid.SetPageid(current_pageid);
rid.SetSlotid(current_slotid);
//设置下一条记录的位置
currentRid->SetPageid(current_pageid);
currentRid->SetSlotid(current_slotid + 1);
return 0;
}
