Scripts generally run so short, and use so few file descriptors that it simply doesn't make sense to close them, since the operating system will close them anyway when the script exits.
Because after it has collected the object, there is no way for you to close the file anymore, and thus you would leak file descriptors. Note that it's not the garbage collector that closes the files. The garbage collector simply executes any finalizers for an object before it collects it. It just so happens that the File class defines a finalizer which closes the file. Because wasted memory is cheap, but wasted file descriptors aren't. Therefore, it doesn't make sense to tie the lifetime of a file descriptor to the lifetime of some chunk of memory.
You simply cannot predict when the garbage collector will run. You cannot even predict if it will run at all : if you never run out of memory, the garbage collector will never run, therefore the finalizer will never run, therefore the file will never be closed. You should always close file descriptors after use, that will also flush it. Often people use File.
For example:. With no associated block, File. If the optional code block is given, it will be passed the opened file as an argument and the File object will automatically be closed when the block terminates.
The value of the block will be returned from File. How are we doing? Please help us improve Stack Overflow. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ruby's File. Asked 10 years, 11 months ago. Active 2 years, 1 month ago. Viewed 71k times. Do we need to explicitly close If yes then why does the GC autoclose?
If not then why the option? Benjamin Gruenbaum k 82 82 gold badges silver badges bronze badges. Your 'common knowledge' has been outdated since destructors were invented. Just a note: While file descriptors are limited, on Linux at least, the limit is quite high. Linuxios : on my ubuntu Bad habit will cause big problem one day! Add a comment. Active Oldest Votes. I saw many times in ruby codes unmatched File. Its implementation basically looks something like like this: def File.
Do we need to explicitly close? If yes then why does the GC autoclose? Community Bot 1 1 1 silver badge. I have a beef with the issue because of stability requirements in my projects..
In this example, should raise be inside the rescue block? The class IO provides all the basic methods, such as read, write, gets, puts, readline, getc, and printf. For more functions, please refer to Ruby Class IO.
In the previous chapters, you have assigned values to variables and then printed the output using puts statement. The puts statement instructs the program to display the value stored in the variable. This will add a new line at the end of each line it writes. The following code shows you how to use the gets statement. This code will prompt the user to enter a value, which will be stored in a variable val and finally will be printed on STDOUT.
Unlike the puts statement, which outputs the entire string onto the screen, the putc statement can be used to output one character at a time. The print statement is similar to the puts statement. The only difference is that the puts statement goes to the next line after printing the contents, whereas with the print statement the cursor is positioned on the same line.
Until now, you have been reading and writing to the standard input and output. Now, we will see how to play with actual data files. You can create a File object using File. Finally, you can use File. You can use File. However, there is one difference in between File. The difference is that the File. Read-only mode. The file pointer is placed at the beginning of the file. This is the default mode. Write-only mode. Overwrites the file if the file exists.
If the file does not exist, creates a new file for writing. Read-write mode. Overwrites the existing file if the file exists. If the file does not exist, creates a new file for reading and writing. The file pointer is at the end of the file if the file exists. That is, the file is in the append mode. If the file does not exist, it creates a new file for writing. Read and write mode.
The file opens in the append mode. If the file does not exist, it creates a new file for reading and writing. So, gets reads a line from standard input, and aFile.
You can use the method sysread to read the contents of a file. You can open the file in any of the modes when using the method sysread.
This statement will output the first 20 characters of the file. The file pointer will now be placed at the 21st character in the file. You can use the method syswrite to write the contents into a file.
0コメント