File I/O operation tutorial in Lua

File I/O operation tutorial in Lua

This article mainly introduces the file I/O operation tutorial in Lua, which is the basic knowledge of Lua beginners. For more information, see

The I/O Library in Lua is used to read and process files. There are two types of file operations, namely, implicit file descriptor and clear file descriptor in Lua.

In the following example, we will use the example file test. lua, as shown in.

The Code is as follows:

-- Sample test. lua

-- Sample2 test. lua

Use the following statement to open a simple file.

The Code is as follows:

File = io. open (filename [, mode])

Various file modes are listed in the following table.

Hidden file descriptor

The hidden file descriptor uses the standard input/output mode, or a single input/output file. An example of using the descriptor of an implicit file is as follows.

The Code is as follows:

-- Opens a file in read

File = io. open ("test. lua", "r ")

-- Sets the default input file as test. lua

Io. input (file)

-- Prints the first line of the file

Print (io. read ())

-- Closes the open file

Io. close (file)

-- Opens a file in append mode

File = io. open ("test. lua", "")

-- Sets the default output file as test. lua

Io. output (file)

-- Appends a word test to the last line of the file

Io. write ("-- End of the test. lua file ")

-- Closes the open file

Io. close (file)

When you run the program, the first line of output of the test. lua file is obtained. In this example, the following output is obtained.

The Code is as follows:

-- Sample test. lua

This is the first line to declare the test. lua file. "-- End of the test. lua file" will be appended to the last line of the test. lua code.

In the above example, we can see how the Implicit description works with the file system io. "×" method. The preceding example uses io. read () without any optional parameters. The optional parameter can be any of the following.

Other common IO methods include:

Io. tmpfile (): returns the read/write temporary file. Once the program exits, the file will be deleted.

Io. type (file): returns a file, closes the file, or returns the input file.

Io. flush (): clears the default output buffer.

Io. lines (optional file name): provides a general loop iterator to traverse the file and close the file that provides the file name and default file in the final case, it is not closed at the end of the loop.

Clear file descriptor

We often use clear file descriptors so that we can process multiple files at the same time. These functions are similar to implicit file descriptors. Here, we use the file: function name, instead of io. function_name. The following example shows the version of the same implicit file descriptor.

The Code is as follows:

-- Opens a file in read mode

File = io. open ("test. lua", "r ")

-- Prints the first line of the file

Print (file: read ())

-- Closes the opened file

File: close ()

-- Opens a file in append mode

File = io. open ("test. lua", "")

-- Appends a word test to the last line of the file

File: write ("-- test ")

-- Closes the open file

File: close ()

When you run the program, the example that will be implicitly described is similar output.

The Code is as follows:

-- Sample test. lua

All the modes in which the file is opened and the parameter is used to read the external description are the same as the descriptor of the hidden file.

Other common file methods include:

File: seek (optional whence, optional offset): parameter "set", "cur" or "end ". Set the position of the file where the new file pointer is updated from the beginning of the file. The offset is zero-based. From the offset measured when the first parameter is "set" at the beginning of the file, from the current location in the "cur" file, or from the end of the file, for "end ". The default parameter values are "cur" and 0. Therefore, the current file location can be obtained by calling the function without parameters.

File: flush (): clears the default output buffer.

Io. lines (optional file name): provides a general loop iterator to traverse the file and close the file that provides the file name and default file in the final case, it is not closed at the end of the loop.

For example, the following method is used. Offsets starts from the end of the file before the cursor at 25 positions. Print the remaining seek position from the file reading function.

The Code is as follows:

-- Opens a file in read

File = io. open ("test. lua", "r ")

File: seek ("end",-25)

Print (file: read ("* "))

-- Closes the opened file

File: close ()

The output is similar to the following.

The Code is as follows:

Sample2 test. lua

-- Test

You can use different modes and parameters to understand the Lua file operation capabilities.