![]() Sequential input from a file is called a data stream. ![]() When records are read from a file, they are accessed sequentially (one after the other), in whatever order they happen to be stored in within the file. The act of opening a file and reading the records it contains into memory can be described as pre-processing, because this action prepares the records for processing. If new data is being added to a file, the records will be added ( appended) to the end of the file, and the existing data will be preserved. If amended records are written back to the same file, the original version of each record will be replaced ( overwritten) by the new version. Writing data to a file is a separate operation in which the file must be re-opened, or a new file created. If records have been modified by a program, the amended records are usually either written back to the same file, or to a another file. Once all of the required records have been read from the file, the file is closed. The results of this processing are normally output to the screen. A typical file processing operation opens a file, reads the records into memory and processes them one at a time. each field is separated from the next by a comma). In text-based data files, the fields in a record are usually comma-delimited (i.e. A customer record, for example, could contain the fields CustomerName, StreetAddress, Town and TelNumber. A record is a single line in a file that consists of one or more fields. We are more interested here, however, in text files that can store records. Text files can be used to store fairly large blocks of text (for example, a short story, a letter, or a poem). The data files we will be working with here will be text files. The commands available to the programmer for file I/O include those required to open and close files, read data from a file, and write the results of any data processing back to a file. This output data may be stored in the same file, or in a new file. New data created by your program, or existing data that has been modified by your program, is the program's output. ![]() File input and output (or file I/O) involves retrieving data (the input) from a file for use in your program. ![]()
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