File Processing in C

1
File Processing in C

• Data is stored in files so that it may be
  retrieved for processing when needed

2
Reading data from files using C

• The commands for reading data from a file are
  (for the most part) very similar to those used to
  read data from the keyboard.
• In order for your program to read from the file,
  you must
• include the fstream header file
• declare a variable of type ifstream
• open the file
• read from the file
• after each read, check for end-of-file using the
  eof() member function
• close the file when access is no longer needed
  (optional, but a good practice)

3
Reading data from files using C

• includeltiostreamgt
• include ltfstreamgt
• using namespace std
• void main()
• ifstream indata // indata is like cin
• int num // variable for input value
• indata.open("example.txt")
• indata gtgt num
• while ( !indata.eof() )
• cout ltlt "The next number is " ltlt num
  ltlt endl
• indata gtgt num // sets EOF flag if
  no value found
• indata.close()
• cout ltlt "End-of-file reached.." ltlt endl

4
Reading data from files using C

• The result

5
Reading data from files using C

• includeltiostreamgt
• include ltfstreamgt
• using namespace std
• void main()
• ifstream indata // indata is like cin
• char letter // variable for input value
• indata.open("example.txt") // opens the
  file
• indata gtgt letter
• while ( letter ! 'Q' )
• cout ltlt letter
• indata gtgt letter
• cout ltlt endl
• indata.close()
• cout ltlt "End-of-file reached.." ltlt endl

6
Reading data from files using C

• The result

7
Writing data in the files using C

• In order for your program to writein the file,
  you must
• include the fstream header file
• declare a variable of type ofstream
• open the file
• Writ in the file
• close the file when access is no longer needed
  (optional, but a good practice)

8
Writing data in the files using C

• include ltiostreamgt
• include ltfstreamgt
• using namespace std
• void main ()
• ofstream myfile
• myfile.open("example.dat")
• myfile ltlt "Writing this to a file.\n"

9
Writing data in the files using C
10
Input/Output with files

• include ltiostreamgt
• include ltfstreamgt
• using namespace std
• void main()
• // To write in a file
• ofstream obj_out("file_05.txt")
• int x
• while(cin gtgt x)
• obj_out ltlt x ltlt endl
• // To stop writing to a file, press CTRLZ
  then ENTER
• // To read from a file
• ifstream obj_in("file_05.txt")
• while(obj_in gtgt x)
• cout ltlt "X from the file is " ltlt x ltlt
  endl
• coutltltendl

11
Input/Output with files
12
Example

• Q1 Write a program that copies a content of a
  file into a one-dimensional array. Assume that
  the content of the file is integers.

13
Solution

• includeltiostreamgt
• includeltfstreamgt
• using namespace std
• void main()
• int x, c0
• ifstream fin1("d\\test.txt", iosin)
• while(fin1gtgtx)
• c
• ifstream fin2("d\\test.txt", iosin)
• int a new intc
• for(int i0 iltc i)
• fin2 gtgt ai
• // To print the content of the array
• for(int i0 iltc i)
• cout ltlt ai ltlt endl

14
Example

• Q2 Write a program that copies a content of a
  file into a one-dimensional array. Assume that
  the content of the file is string.

15
Solution

• includeltiostreamgt
• includeltfstreamgt
• using namespace std
• void main()
• string x int c0
• ifstream fin1("test.txt", iosin)
• while(fin1gtgtx)
• c
• fin1.close()
• ifstream fin2("test.txt", iosin)
• string a new stringc
• for(int i0 iltc i)
• fin2 gtgt ai
• // To print the content of the array
• for(int i0 iltc i)
• cout ltlt ai ltlt endl