O 1 for arrays. The other thing is, on a lower level, accessing array element 3 and then is slower than accessing array element 3, then 4, then 5. Okay I understand, but I can't really control the order in which the elements will be accessed, what I want is the O 1 efficiency. If you would use a hash index you would theoretically get this O 1 access.
You are talking about constant time, but you mention a unique incrementing primary key. Then benchmark against a database lookup. Cade Roux Cade Roux Yes, it's just an array of strings, the indices are gapless. Both answers are very good, but the idea to use the file-system and benchmark against the DB lookup is what I plan to do.
Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name. Email Required, but never shown. The Overflow Blog. Stack Gives Back Safety in numbers: crowdsourcing data on nefarious IP addresses. A file represents a sequence of bytes on the disk where a group of related data is stored. File is created for permanent storage of data.
It is a ready made structure. In C language, we use a structure pointer of file type to declare a file. A file is a space in a memory where data is stored. A mechanism of manipulating with the files is called as file management. A file must be opened before performing operations on it. A file can be opened in a read, write or an append mode. In this case, random access to file can be used , which allows to access any record directly at any position in the file.
This function is used for setting the file pointer at the specified byte. While both binary and text files contain data stored as a series of bits binary values of 1s and 0s , the bits in text files represent characters, while the bits in binary files represent custom data. While text files contain only textual data, binary files may contain both textual and custom binary data.
A binary file is a file that uses all 8 bits of a byte for storing the information. It is the form which can be interpreted and understood by the computer. It returns the current position in long type and file can have more than bytes of data.
To read binary data files , define the variables, open the file for reading , and read the bytes into those variables. Each variable reads as many bytes out of the file as required by the specified data type and organizational structure. A random access file behaves like a large array of bytes. There is a cursor implied to the array called file pointer, by moving the cursor we do the read write operations.
This part of the file consists of raw data with no header or key information. The database file ends on the last block of the last record in the file, so there is no extra space at the end of the file. The file grows and shrinks as records are added and deleted. The size allocated to a record does not always correspond to the actual amount of data the record contains. The record can be thought of as a container -- it may be only partially full. Valid record data is positioned at the start of the record.
Before we step through the source code, let's go over the chosen algorithms for each of these operations:. This operation retrieves a requested record from the file based on a key. To retrieve a record, we:. This operation updates an existing record with new data, replacing the new data with the old. The steps for our update vary, depending on the size of the new record data.
If the new data fits into the existing record, we:. Reclaim the space allocated to the record being removed by either shrinking the file, if the record is the last one in the file, or by adding its space to an adjacent record. Ensure capacity. This operation makes sure the index region is large enough to accommodate additional entries.
In a loop, we move records from the front to the end of the file until there is sufficient space. To move one record we:. Locate the record header of the first record in the file; note that this is the record with data at the top of the record data region -- not the record with the first header in the index.
Grow the file by the size of the target record's data by using the setLength long method in RandomAccessFile. We're now ready to get our hands dirty and work through the code for the example. You can download the complete source from Resources. BaseRecordsFile is an abstract class and is the main implementation of our example. It defines the main access methods as well as a slew of utility methods for manipulating records and index entries. Here are the latest Insider stories. More Insider Sign Out.
Sign In Register. To me programming is more than point and click it is actually typing in your code to get it to work. You really want to be using SQLServer in some capacity unless what you want to do is write a server to have the experience of doing so. Unfortunately I have very limited experience in programming, I have done some unfortunately most recently I have done it with QBasic 4. With that program I could simply do what I need to do and it would work wonderfully, unfortunately it is not as cosmetic and I would have to create a mouse driver.
I need whatever information I require to get it to work I spent about 3 weeks a while ago trying to get the blasted thing to do anything over a network only to be told by VBExpress that I could not do this type of file over a network. The content you requested has been removed. Ask a question. Quick access. Search related threads. Remove From My Forums. Answered by:.
0コメント