Lua file I/O

The Lua I/O library is used to read and process files.Divided into simple mode (same as C), full mode.

• The simple model has a current input file and a current output file, and provides operations related to these files.
• The complete model is implemented using an external file handle.It defines all file operations as methods on the file handle in an object-oriented form

Simple mode is more suitable for doing some simple file operations.However, when performing some advanced file operations, the simple mode seems powerless.For operations such as reading multiple files at the same time, it is more appropriate to use full mode.Friends who need the framework source code can see my profile and contact me.

The open file operation statement is as follows:

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

The values ​​for mode are:

Simple Mode

Simple mode uses standard I/O or uses one current input file and one current output file.

The following is the code of the file.lua file, the operating file is test.lua (if not, you need to create the file), the code is as follows:

Instance

-- open the file as read-onlyfile = io.open("test.lua", "r")-- set the default input file to test.luaio.input(file)-- output the first line of the fileprint(io.read())-- close open filesio.close(file)-- open a write-only file in append modefile = io.open("test.lua", "a")-- set default output file to test.luaio.output(file)-- Add a Lua comment to the last line of the fileio.write("-- comment at the end of test.lua file")-- close open filesio.close(file)

Execute the above code, you will find that the first line of information in the test.lua file is output, and the lua comment is added to the last line of the file.As my output here is:

-- test.lua file

In the above example we used the io."x" method, in which we did not take parameters in io.read(), the parameters can be one of the following table:

Other io methods are:

• io.tmpfile():Returns a handle to a temporary file opened in update mode and automatically deleted when the program ends

• io.type(file): Check if obj is an available file handle

• io.flush(): Writes all buffered data to file

• io.lines(optional file name): Returns an iterative function, each call will get a line of content in the file, when it reaches the end of the file, it will return nil, but notclose file

Full Mode

Often we need to process multiple files at the same time.We need to use file:function_name instead of io.function_name method.The following example demonstrates how to process the same file at the same time:

Instance

-- open the file as read-onlyfile = io.open("test.lua", "r")-- output the first line of the fileprint(file:read())-- close open filesfile:close()-- open a write-only file in append modefile = io.open("test.lua", "a")-- Add a Lua comment to the last line of the filefile:write("--test")-- close open filesfile:close()

Execute the above code, you will find that the first line of information in the test.lua file is output, and the lua comment is added to the last line of the file.As my output here is:

-- test.lua file

The arguments to read are the same as in simple mode.

Other methods:

• file:seek(optional whence, optional offset): Set and get the current file position, return the final file position (in bytes) if successful, nil plus error if failedinformation.The parameter whence value can be:

  • "set": start at the beginning of the file
  • "cur": start at current position [default]
  • "end": start from end of file
  • offset:default is 0
  Without parameter file:seek() returns the current position, file:seek("set") locates the file header, file:seek("end") locates the file end and returns the file size

for line in io.lines("main.lua") doprint(line)end

The following example uses the seek method, locates the 25th position from the bottom of the file and uses the *a parameter of the read method, that is, reads the entire file from the current position (the 25th position from the bottom).

Instance

-- open the file as read-onlyfile = io.open("test.lua", "r")file:seek("end",-25)print(file:read("*a"))-- close open filesfile:close()

The result I output here is:

st.lua end of file --test