var q cfopenreadwholefileIo Library Tutorial. Input and Output Facilities. The IO library provides two different styles for file manipulation. The first one uses implicit file descriptors, that is, there are operations to set a default input file and a default output file, and all inputoutput operations are over those default files. The second style uses explicit file descriptors. When using implicit file descriptors, all operations are supplied by table io. When using explicit file descriptors, the operation io. The table io also provides three predefined file descriptors with their usual meanings from C io. A file descriptor is a userdata containing the file stream FILE, with a distinctive metatable created by the IO library. Unless otherwise stated, all IO functions return nil on failure plus an error message as a second result and some value different from nil on success. This function opens a file, in the mode specified in the string mode. It returns a new file descriptor, or, in case of errors, nil plus an error message. The mode string can be any of the following. The mode string may also have a b at the end, which is needed in some systems to open the file in binary mode. This string is exactly what is used in the standard C function fopen. Equivalent to file close. Without a file, closes the default output file. Equivalent to file flush over the default output file. When called with a file name, it opens the named file in text mode, and uses it as the default input descriptor. PDF files that contain the Visual Studio 2005 documentation. Sample Interview Questions Interview Questions. This page lists some common interview questions for software engineers. Questions. Click on the question to see its. Return if a given file range contains data or holes filled with zeroes. This uses the filesystem capabilities of querying which regions of a sparse file are allocated. When called with a file descriptor, it simply sets that file descriptor as the default input file. When called without parameters, it returns the current default input file descriptor. In case of errors this function raises the error, instead of returning an error code. Opens the given file name in read mode and returns an iterator function that, each time it is called, returns a new line from the file. Therefore, the construction. When the iterator function detects the end of file, it closes the file and returns nil to finish the loop. The call io. lines without a file name is equivalent to io. Similar to io. input, but operates over the default output file. Equivalent to io. Returns a descriptor for a temporary file. This file is open in update mode and it is automatically removed when the program ends. Checks whether obj is a valid file descriptor. Returns the string file if obj is an open file descriptor, closed file if obj is a closed file descriptor, and nil if obj is not a file descriptor. Equivalent to io. If I have a large binary file say it has 100,000,000 floats, is there a way in C or C to open the file and read a specific float, without having to load the. As stefan said using fopen with w mode will do the job for you. When you open a file with w flag it creates an empty file for writing. If a file with the same. Saves any written data to file f. Returns an iterator function that, each time it is called, returns a new line from file f. Therefore, the construction. Unlike io. lines, this function does not close the file when the loop ends. Reads the file f, according to the given formats, which specify what to read. For each format, the function returns a string or a number with the characters read, or nil if it cannot read data with the specified format. When called without formats, it uses a default format that reads the entire next line see below. The available formats are. On end of file, it returns the empty string. This is the default format. If number is zero, it reads nothing and returns an empty string, or nil on end of file. Sets and returns the index position for file f, measured from the beginning of the file, to the position given by offset plus a base specified by the string whence, as follows. In case of success, function seek returns the final file position, measured in bytes from the beginning of the file. If this function fails, it returns nil, plus a string describing the error. The default value for whence is cur, and for offset is 0. Therefore, the call file seek returns the current file position, without changing it the call file seekset sets the position to the beginning of the file and returns 0 and the call file seekend sets the position to the end of the file, and returns its size. Writes the value of each of its arguments to file f. The arguments must be strings or numbers. To write other values, use tostring or string. See Also. Recent. Changes preferencesedit history. Last edited September 1.