深度学习-读取图像特征库LevelDB中的数据

本文介绍如何利用C++代码遍历存储在LevelDB中的图像特征数据,并提供了两种编译C++代码的方法以及运行程序的步骤。

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上个博客中,提取出了图像特征并存储于LevelDB库中,因此,相读取出来

1.通过C++代码遍历LevelDB库
    #include <cassert>  
    #include <iostream>  
    #include <string>  
    #include <cstdlib>  
      
    #include <leveldb/db.h>  
      
    int main()  
    {  
        leveldb::DB *db;  
        leveldb::Options options;  
        leveldb::Status status;  
      
        std::string key1 = "";  
        std::string val1 = "val1", val;  
      
        options.create_if_missing = true;  
        status = leveldb::DB::Open(options, "/home/lw/caffe/examples/_temp/features", &db);  

        if (!status.ok())  
        {  
            std::cout << status.ToString() << std::endl;  
            exit(1);  
        }  
      
        //迭代遍历
	leveldb::Iterator* it = db->NewIterator(leveldb::ReadOptions());
	for (it->SeekToFirst(); it->Valid(); it->Next()) {
  		std::cout << it->key().ToString() << ": "  << it->value().ToString() << std::endl;  
	}
	assert(it->status().ok());   
	delete it;
        
        std::cout << "Get val: " << val1 << std::endl;  
      

 	// close 
    	delete db;  
        return 0;  
    }  


2.编译C++代码

这有两种方法
a.
g++ -o test/myexe test/test.cpp -I leveldb/out-shared/  -I leveldb/include/ -lleveldb


b.
如果前面将库拷贝到/usr/include及/usr/lib中,则可以省略后面的-I及-L
然后sudo cp out-shared/libleveldb.so* /usr/local/lib & sudo cp -R include/* /usr/local/include

在终端执行
g++ -o test/myexe test/test.cpp  -lleveldb

3,运行:
./test/myexe
leveldb实现解析 淘宝-核心系统研发-存储 那岩 neveray@gmail.com 2011-12-13 目录 一、 代码目录结构 ....................................................................... 1 1. doc/ ............................................................................ 1 2. include/leveldb/ ................................................................. 1 3. db/ ............................................................................. 1 4. table/........................................................................... 1 5. port/ ........................................................................... 1 6. util/ ........................................................................... 1 7. helper/memenv/ ................................................................... 1 二、 基本概念 .......................................................................... 1 1. Slice (include/leveldb/slice.h) .................................................. 1 2. Option (include/leveldb/option.h) .............................................. 2 3. Env (include/leveldb/env.h util/env_posix.h) .................................... 3 4. varint (util/coding.h) ........................................................... 3 5. ValueType (db/dbformat.h) ...................................................... 3 6. SequnceNnumber (db/dbformat.h) ................................................. 4 7. user key......................................................................... 4 8. ParsedInternalKey (db/dbformat.h) .............................................. 4 9. InternalKey (db/dbformat.h) ...................................................... 4 10. LookupKey (db/dbformat.h) ........................................................ 4 11. Comparator (include/leveldb/comparator.h util/comparator.cc) .................... 4 12. InternalKeyComparator (db/dbformat.h) ............................................ 5 13. WriteBatch (db/write_batch.cc) ................................................. 5 14. Memtable (db/memtable.cc db/skiplist.h) .......................................... 5 15. Sstable (table/table.cc) ......................................................... 5 16. FileMetaData (db/version_edit.h) ............................................... 5 17. block (table/block.cc) ........................................................... 6 18. BlockHandle(table/format.h) ...................................................... 6 19. FileNumber(db/dbformat.h) ...................................................... 6 20. filename (db/filename.cc) ........................................................ 6 21. level-n (db/version_set.h) ....................................................... 7 22. Compact (db/db_impl.cc db/version_set.cc) ........................................ 7 23. Compaction(db/version_set.cc) .................................................... 7 24. Version (db/version_set.cc) ...................................................... 8 25. VersionSet (db/version_set.cc) ................................................. 9 26. VersionEdit(db/version_edit.cc) ................................................. 10 27. VersionSet::Builder (db/version_set.cc) ......................................... 11 28. Manifest(descriptor)(db/version_set.cc)...................................... 12 29. TableBuilder/BlockBuilder(table/table_builder.cc table/block_builder.cc) ......... 12 30. Iterator (include/leveldb/iterator.h) ........................................... 12 三、 存储结构的格式定义与操作 .......................................................... 12 1. memtable (db/skiplist.h db/memtable) ............................................ 12 2. block of sstable (table/block_builder.cc table/block.cc) ......................... 14 3. sstable (table/table_bulder.cc/table.cc) ........................................ 16 4. block of log (db/log_format.h db/log_writer.cc db/log_reader.cc) .............. 18 5. log (db/log_format.h db/log_writer.cc db/log_reader.cc) ........................ 18 6. cache(util/cache.cc) .......................................................... 19 7. Snapshot (include/leveldb/snapshot.h) ......................................... 19 8. Iterator (include/leveldb/iterator.h) ........................................... 19 四、 主要流程 ......................................................................... 24 1. open ........................................................................... 24 2. put ............................................................................ 25 3. get ............................................................................ 25 4. delete.......................................................................... 26 5. snapshot........................................................................ 26 6. NewIterator ..................................................................... 26 7. compact......................................................................... 26 五、 总结 ............................................................................. 30 1. 设计/实现中的优化 ............................................................... 30 2. 可以做的优化 .................................................................... 31
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