问题
I have two programs that will be reading / writing files to the same directory at the same time (but not to the same exact files at the same time). I have the writing portion done, but I am struggling to get a half way decent and working implementation of the reading directory portion.
The files within the directory follow the following naming scheme:
Image-[INDEX]-[KEY/DEL]--[TIMESTAMP]
[INDEX] increments up from 000000, [KEY/DEL] alternates based on whether the image is a key or a delta frame and [TIMESTAMP] is the Unix / Linux epoch time at file creation.
Right now, the reading program reads in the directory (using the dirent.h library) one file at a time every time it needs to find an image within the directory. When the directory gets extremely large, I would imagine that this operation / method will quickly become extremely resource intensive, and eventually fail. So, I am trying to find an alternative method. I was thinking of reading in the entire directory at initialization, and saving the file information in an array to access / use later in the program. Then, when a file is requested that is not in the array, the program would go and update the array of files by reading in the directory, but this time starting from the point it left off at the end of the initialization.
Is this possible? To start reading in the file names within a directory at a known point (the last file "read in") in the directory? Or do I have to start all the way from the beginning each time?
Or is there a better way of doing this?
Thanks.
回答1:
As Andrew said, I would confirm that this is actually a problem before trying to solve it.
If you can discount the possibility of files being created out of sequence, that is, no file you wish to process before another file will ever be created after that file, then you can use this method.
First, read the entire directory listing into an array or vector. Then, when iterating files, just iterate the vector. Finally, if you get a file not found or reach the end of the vector, refresh it just in case more have been created.
You will no doubt want to encapsulate this logic into some sort of context object, which remembers the last file read. You could also optimise by sorting the vector.
来源：https://stackoverflow.com/questions/15348532/read-in-a-directory-from-a-given-file-point-in-c