Text and Binary Files

1. Text and Binary Files Reading and Writing Comp1 notes

2. Making data persistent • When a program finishes, the data stored in variables is lost. • Data can be stored in several ways. • Text files • csv files • Binary files • Databases Comp1 notes

3. What you need to know • csv files • what it is • to read records from a csv file • to write records to a csv file • data files • what it is • to read records from a data file • to write records to a data file Comp1 notes

4. What is a csv file? • Printable characters • Separator between values • Comma • Tab & others are sometimes used • End of line marker Use a spreadsheet and save as csv to make a csv file quickly Comp1 notes

5. Writing to a text file • Must include IO library Imports System.IO • Declare a writing channel Dim CFW As StreamWriter • Link the file pathname to the channel Filename = “C:\My files\myCsvFile.txt” CFW = New StreamWriter(Filename) • Write a line of text to the channel CFW.WriteLine(“This is a string of text”) • Close the channel CFW.Close() Comp1 notes

6. Writing to a csvfile • Create a string, using a comma to separate the fields Textstring = (Name & “,” & Telno & “,” & AvPtSc) • Write the string to the file CFW.WriteLine(Textstring) Comp1 notes

7. Reading from a text file • Must include IO library Imports System.IO • Declare a writing channel Dim CFR As StreamReader • Link the file pathname to the channel Filename = “C:\My files\myCsvFile.txt” CFR = New streamReader(Filename) • Read a line of text from the channel MyString = CFR.ReadLine() • Checkfor end of file CFR.EndOfStream ‘returns boolean • Close the channel CFR.Close() Comp1 notes

8. Reading from a csv file • You don’t need to know how to use classes to handle csv files. • You do need to know how to handle string functions such as: • length • position • substring • concatenation Comp1 notes

9. Your mission • Use your Student Record and Student Group array from last lesson • Add five Students • Create a csv file • Write code to write your students to the file • Open your file in a spreadsheet to check • Add 5 more students to the spreadsheet • Write code to read these back into your program as student records and output the whole group to the console window. Comp1 notes