多个文件合并的C++实现

[Hongfei Yan]

打开多个文件合并的C++实现，上课时候是问这个问题吧？

我在JIANGHan程序中找了一段，请看是否有帮助。

void IndexWriter::mergePSTBlk(int numtmps) {

  string prefix = path+"/"+POSTINGS_FILE;

  ofstream merge_trm, merge_doc, merge_pos, merge_tmap;

  set<pair<string, int> > termheap;

  ifstream tmp_files[numtmps*3];

  merge_trm.open((prefix+".trm").c_str());

  merge_doc.open((prefix+".doc").c_str(), ios::binary);

  merge_pos.open((prefix+".pos").c_str(), ios::binary);

  merge_tmap.open((path+"/"+TERM_MAP_FILE).c_str());

  for (int i = 0; i < numtmps; i++) {

    tmp_files[i*3].open((prefix+".trm."+itoa(i)).c_str());

    tmp_files[i*3+1].open((prefix+".doc."+itoa(i)).c_str(), ios::binary);

    tmp_files[i*3+2].open((prefix+".pos."+itoa(i)).c_str(), ios::binary);

  }

  for (int i = 0; i < numtmps; i++) {

    ifstream& ftrm = tmp_files[i*3];

    string term;

    if (ftrm >> term) {

      termheap.insert(make_pair(term, i));

    }

  }

  int num_term = 0;

  while (!termheap.empty()) {

    set<pair<string, int> >::iterator it = termheap.begin();

    pair<string, int> head = *it;

    set<int> hit;

    int num_docs = 0;

    merge_tmap << num_term << " " << head.first << endl;

    merge_trm  << num_term << " " << ftellp(merge_doc) << endl;

    num_term++;

    while (!it->first.compare(head.first)) {

      unsigned ndoc, i = it->second;

      string term;

      ifstream& ftrm = tmp_files[i*3];

      ifstream& fdoc = tmp_files[i*3+1];

      hit.insert(i);

      if (ftrm >> term) {

        termheap.insert(make_pair(term, i));

      }

      fpeek(fdoc, &ndoc, sizeof(ndoc));

      num_docs += ndoc;

      termheap.erase(it);

      if (!termheap.empty()) {

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