This document discusses file opening modes and handling strings in files in C programming. It explains different modes for opening files, including read, write, append, append plus, read plus, and write plus modes. It also covers how to write and read strings from files, noting that handling strings in files is as easy as handling characters. The different file opening modes specify whether the file can be read from, written to, modified, or if writing will overwrite an existing file or create a new one.

1. Lecture 22Lecture 22
Version 1.0Version 1.0
More on FilesMore on Files

2. 2Rushdi Shams, Dept of CSE, KUET, Bangladesh
A File Copy ProgramA File Copy Program
 We will take a look at how you read from a fileWe will take a look at how you read from a file
 And then how you can put the content of thatAnd then how you can put the content of that
file into another filefile into another file

3. 3Rushdi Shams, Dept of CSE, KUET, Bangladesh

4. 4Rushdi Shams, Dept of CSE, KUET, Bangladesh
File Opening ModesFile Opening Modes
 Read (r)Read (r)
Searches the fileSearches the file
If the search is successfulIf the search is successful
load the file into memoryload the file into memory
set a pointer at the beginning of the fileset a pointer at the beginning of the file
If the file cannot be openedIf the file cannot be opened
returns NULLreturns NULL
Only reads from fileOnly reads from file

5. 5Rushdi Shams, Dept of CSE, KUET, Bangladesh
File Opening ModesFile Opening Modes
 Write (w)Write (w)
Searches the fileSearches the file
If the file existsIf the file exists
it is overwrittenit is overwritten
If notIf not
a new file is createda new file is created
If the file cannot be openedIf the file cannot be opened
returns NULLreturns NULL
Only writes to fileOnly writes to file

6. 6Rushdi Shams, Dept of CSE, KUET, Bangladesh
File Opening ModesFile Opening Modes
 Append (a)Append (a)
Searches the fileSearches the file
If the search is successfulIf the search is successful
load the file into memoryload the file into memory
set a pointer at the end of the fileset a pointer at the end of the file
If the file cannot be openedIf the file cannot be opened
returns NULLreturns NULL
Adding new contents in the fileAdding new contents in the file

7. 7Rushdi Shams, Dept of CSE, KUET, Bangladesh
File Opening ModesFile Opening Modes
 Append Plus (a+)Append Plus (a+)
Searches the fileSearches the file
If the search is successfulIf the search is successful
load the file into memoryload the file into memory
If not foundIf not found
create a new filecreate a new file
If the file cannot be openedIf the file cannot be opened
returns NULLreturns NULL
Reading, appending in fileReading, appending in file
Cannot modifyCannot modify

8. 8Rushdi Shams, Dept of CSE, KUET, Bangladesh
File Opening ModesFile Opening Modes
 Read Plus (r+)Read Plus (r+)
Searches the fileSearches the file
If the search is successfulIf the search is successful
load the file into memoryload the file into memory
set a pointer at first characterset a pointer at first character
If the file cannot be openedIf the file cannot be opened
returns NULLreturns NULL
Reading, writing, modifying contents in the fileReading, writing, modifying contents in the file

9. 9Rushdi Shams, Dept of CSE, KUET, Bangladesh
File Opening ModesFile Opening Modes
 Write Plus (w+)Write Plus (w+)
Searches the fileSearches the file
If the file existsIf the file exists
it is overwrittenit is overwritten
If notIf not
a new file is createda new file is created
If the file cannot be openedIf the file cannot be opened
returns NULLreturns NULL
Writing, reading and modifying contentsWriting, reading and modifying contents

10. 10Rushdi Shams, Dept of CSE, KUET, Bangladesh
String in FilesString in Files
 So far we have seen how to manipulateSo far we have seen how to manipulate
characters in filescharacters in files
 Now, we will see that handling strings in files isNow, we will see that handling strings in files is
as easy as handling charactersas easy as handling characters
 At first we will see how to write strings into aAt first we will see how to write strings into a
filefile

11. 11Rushdi Shams, Dept of CSE, KUET, Bangladesh

12. 12Rushdi Shams, Dept of CSE, KUET, Bangladesh
 Now we will see how to read strings from filesNow we will see how to read strings from files

13. 13Rushdi Shams, Dept of CSE, KUET, Bangladesh