memory mapped files c tutorial

File Operations are indispensable. However, memory ing is often used in mass data storage and limited resource systems. Through file ing, all or part of the disk file is mapped to a region in the virtual address space of the process. You can directly access the mapped file, instead of performing read/write or other file I/O operations, you do not need to buffer t

E.printstacktrace (); Long T=system.currenttimemillis ()-t1; System.out.println ("Sum:" +sum+ "Time:" +t); catch (FileNotFoundException e) {//TODO auto-generated catch block E.printstacktrace (); } Mappedbytebuffer Buffer=null; try {buffer=new randomaccessfile ("/home/tobacco/test/res.txt", "RW"). Getchannel (). Map (FileChannel.MapMode.READ_ WRITE, 0, 1253244); int sum=0; int n; Long T1=system.currenttimemillis (); for (int i=0;i Te

For some small files, the use of common file streams can be a good solution, but for large files, such as 2 GB or more, the file stream will not work, therefore, you need to use the memory ing method of the API. Even the memory ing cannot map the size of all files at a time.

On Windows, memory ing files make reading and writing of large files not consume too much memory, but also reduce frequent cpu commands. In addition, data is shared between processes on windows through memory ing files.In this case, we need to load tens of megabytes of small

C ++ uses memory file ing to read and write files I need to read and write 2 TB of data each time recently, so I found a solution. I hope you will be familiar with reading files. It can be used one day. Handle m_handle_file = createfile (strfilepath, generic_read | generic_write, 0, null, open_existing, file_attribute_normal, null );If (m_handle_file = invalid_

Python's API to read and write files is simple, and it's easy to step on the pit when you're not careful. The author records a step of the pit process, and gave some summary, I hope to everyone in the process of using Python, can avoid some of the potential pitfalls of code. 1.read () and ReadLines (): A tutorial that searches Python for read and write files,

program.④. Code segmentA code segment is an operation command used to store executable files, that is, it is an image of the executable program in the memory. The code segment must be prevented from being modified illegally at runtime. Therefore, only read operations are allowed, but write (Modify) operations are not allowed. For example, the functions in the program are stored in the memory.Object Data is

(IOException e ){// TODO Auto-generated catch blockE. printStackTrace ();}Long t = System. currentTimeMillis ()-t1;System. out. println ("sum:" + sum + "time:" + t );} Catch (FileNotFoundException e ){// TODO Auto-generated catch blockE. printStackTrace ();}MappedByteBuffer buffer = null;Try {Buffer = new RandomAccessFile ("/home/tobacco/test/res.txt", "rw"). getChannel (). map (FileChannel. MapMode. READ_WRITE, 0, 1253244 );Int sum = 0;Int n;Long t1 = System. currentTimeMillis ();For (int I =

SQLite tutorial (10): Memory Database and temporary database, sqlite tutorial I. Memory Database: In SQLite, databases are usually stored in disk files. However, in some cases, we can keep the database in the memory. The most comm

that the file should be mapped to the start address of the process space and is typically assigned a null pointer, at which point the task of selecting the start address is left to the kernel. The return value of the function is the address that the last file maps to the process space, and the process can manipulate the starting address directly to the valid address of the value. Incidentally, let's introduce the Shm_open and Shm_unlink two funct

You can estimate the size of each file as 5g*64=300g, far greater than4G. So it is not possible to fully load it into memory for processing. Consider adopting a divide-and-conquer approach. Traversing filesA, for eachURL FetchHash (URL)%1000, and then, based on the resulting value,URLs are stored separately in the1000 Small files (set toA0,A1,... a999). So the size of each small file is about300m. Traverse

Benefits of MMAP: There will be no unrelated copies compared to read and write system calls; Without errors, there will be no overhead such as system calls and operating environment switching; Lseek is no longer required. Disadvantages of MMAP: Memory ing is always an integer multiple of pagesize, which wastes a certain amount of memory; If the content to be map