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Слайды и текст этой презентации

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Programming Logic and Design Seventh Edition Chapter 7 File Handling and Applications

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Objectives In this chapter, you will learn about: Computer files The data hierarchy Performing file operations Sequential files and control break logic Merging files Master and transaction file processing Random access files

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Understanding Computer Files Computer file A collection of data stored on permanent storage devices such as DVDs, USB drives, and reels of magnetic tape Text files (numbers, names, salaries) that can be read by a text editor Binary files (images and music) File size measured in bytes Byte (one character), kilobyte (thousands of bytes), megabyte (millions of bytes), gigabyte (billions of bytes), terabyte (trillions of bytes)

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Understanding Computer Files (continued) Organizing files Directories and folders Organization units on storage devices Path Combination of disk drive plus the complete hierarchy of directories Example: C:\Logic\SampleFiles\PayrollData.dat

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Understanding the Data Hierarchy Data hierarchy Describes the relationships between data components Consists of: Characters Fields Records Files

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Performing File Operations Use data files in your programs Declaring a file InputFile employeeData OutputFile updatedData Opening a file open employeeData "EmployeeData.dat" Reading data from a file input name from employeeData input address from employeeData input payRate from employeeData

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Performing File Operations (continued) Figure 7-2 Reading three data items from a storage device into memory

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Performing File Operations (continued) Writing data to a file output name, address, payRate to employeeData Closing a file Always close every file you open

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A Program that Performs File Operations Backup file A copy that is kept in case values need to be restored to their original state Called a parent file A newly revised copy is a child file Sorting The process of placing records in order by the value in a specific field or fields

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Understanding Sequential Files and Control Break Logic Sequential file Records are stored one after another in some order Understanding control break logic A control break is a temporary detour in a program A control break program uses a change in a value to initiate special actions or processing A control break report groups similar data together Input records must be in sequential order

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Understanding Sequential Files and Control Break Logic (continued) Figure 7-4 A control break report with totals after each state

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Understanding Sequential Files and Control Break Logic (continued) Examples of control break reports All employees listed in order by department number, with a new page started for each department All books for sale in a bookstore listed in order by category (such as reference or self-help), with a count following each category of book All items sold in order by date of sale, with a different ink color for each new month

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Understanding Sequential Files and Control Break Logic (continued) Single-level control break A detour based on the value of a single variable Uses a control break field to hold the previous value

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Figure 7-5 Mainline logic and getReady() module for the program that produces clients by state report Figure 7-5 Mainline logic and getReady() module for the program that produces clients by state report

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Figure 7-6 The produceReport() and controlBreak() modules for the program that produces clients by state Figure 7-6 The produceReport() and controlBreak() modules for the program that produces clients by state

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Understanding Sequential Files and Control Break Logic (continued) Figure 7-7 The finishUp()module for the program that produces clients by state report

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Merging Sequential Files Merging files Combining two or more files while maintaining the sequential order Examples A file of current employees in ID number order, and a file of newly hired employees also in ID number order A file of parts manufactured in the Northside factory in part-number order, and a file of parts manufactured in the Southside factory also in part-number order

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Merging Sequential Files (continued) Two conditions required for merging files Each file has the same record layout Sorted in the same order based on the same field Ascending order (lowest to highest values) Descending order (highest to lowest values)

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Merging Sequential Files (continued) Figure 7-8 Sample data contained in two customer files

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Mainline logic similar to other file-processing programs, except for handling two files Mainline logic similar to other file-processing programs, except for handling two files With two input files, must determine when both files are at eof Define a flag variable to indicate that both files have reached eof Must define two input files Read one record from each input file

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Figure 7-10 Mainline logic of a program that merges files Figure 7-10 Mainline logic of a program that merges files

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Figure 7-12 Start of merging process Figure 7-12 Start of merging process

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Figure 7-13 Continuation of merging process Figure 7-13 Continuation of merging process

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Master and Transaction File Processing Some related files have a master-transaction relationship Master file Holds relatively permanent data Transaction file Contains temporary data to be used to update the master file Update the master file Changes to values in its fields based on transactions

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Master and Transaction File Processing (continued) Examples A library maintains a master file of all patrons and a transaction file with information about each book or other items checked out A college maintains a master file of all students and a transaction file for each course registration A telephone company maintains a master file of every telephone line (number) and a transaction file with information about every call

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Master and Transaction File Processing (continued) Updating approaches Change information in master file Copy master file and change new version Begin with both files sorted in the same order on the same field

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Figure 7-16 The housekeeping() module for the master-transaction program, and the modules it calls Figure 7-16 The housekeeping() module for the master-transaction program, and the modules it calls

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Figure 7-17 The updateRecords() module for the master-transaction program Figure 7-17 The updateRecords() module for the master-transaction program

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Master and Transaction File Processing (continued) Figure 7-18 Sample data for the file-matching program

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Random Access Files Batch processing Involves performing the same tasks with many records, one after the other Uses sequential files Real-time applications Require that a record be accessed immediately while a client is waiting Interactive program A program in which the user makes direct requests

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Random Access Files (continued) Random access files Records can be located in any order Instant access files Locating a particular record directly Also known as direct access files

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Summary Computer file A collection of data stored on a nonvolatile device in a computer system Data items are stored in a hierarchy Using a data file Declare, open, read, write, close Sequential file: records stored in some order Merging files combines two or more files Maintains the same sequential order

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Summary Master files Hold permanent data Updated by transaction files Real-time applications Require random access files Records stored in any order Records accessed immediately