Formatted Output

1
Formatted Output
Lect15

• Tabs
• include ltstdio.hgt
• int main()
• printf(" 111111111122222222223\n")
• printf("123456789012345678901234567890\n")
• printf("W\tX\tY\tZ\n")
• system("PAUSE") return 0
• Output
• 111111111122222222223
• 123456789012345678901234567890
• W X Y Z

2
int and float Output

• printf(" 111111111122222222223\n")
• printf("123456789012345678901234567890\n")
• printf("d\td\td\td\n",1, 10, 100, 1000)
• printf("f\tf\tf\n",1.0, 10.0, 100.0)
• Output
• 111111111122222222223
• 123456789012345678901234567890
• 1 10 100 1000
• 1.000000 10.000000 100.000000

3
Table

• printf("Time\tVelocity\tAcceleration\n")
• printf("f\tf\tf\n",1.0, 10.0, 100.0)
• Output
• 111111111122222222223
• 123456789012345678901234567890
• Time Velocity Acceleration
• 1.000000 10.000000 100.000000
• Cure
• printf("Time\t\tVelocity\tAcceleration\n")

4
Ragged Tables

• printf("f\tf\tf\n",1.0, 10.0, 100.0)
• printf("f\tf\tf\n",200.0, 2.0, 20.0)
• Output
• 1.000000 10.000000 100.000000
• 200.000000 2.000000 20.000000

5
Field Definitions

• printf("7.2f\t7.2f\t7.2f\n",1.0, 10.0, 100.0)
• printf("7.2f\t7.2f\t7.2f\n",200.0, 2.0, 20.0)
• Output
• 1.00 10.00 100.00
• 200.00 2.00 20.00
• Definition T.Df
• T total number of characters
• D number of characters after the decimal point.

6
Rounding

• float pi3.14159
• printf("f\n",pi) 3.141590
• printf(".5f\n",pi) 3.14159
• printf(".4f\n",pi) 3.1416
• printf(".3f\n",pi) 3.142
• printf(".2f\n",pi) 3.14

7
Minimum Field Size

• int i123
• printf("123456789\n") 123456789
• printf("d\n",i) 123
• printf("6d\n",i) 123
• printf("5d\n",i) 123
• printf("4d\n",i) 123
• printf("3d\n",i) 123
• printf("2d\n",i) 123

8
and -

• int i123
• printf("123456789\n") 123456789
• printf("6d\n",i) 123
• printf("6d\n",i) 123
• printf("-6d\n",i) 123

9
e, E, g, G

• float f11234567.0, f2123.4567
• printf("f, f\n",f1, f2)
• printf("e, 9.3E\n",f1, f2)
• printf("g, G\n",f1, f2)
• Output
• 1234567.000000, 123.456703
• 1.234567e06, 1.235E02
• 1.23457e06, 123.457

10
Files

• Files are used for permanent and temporary
  storage of various items
• Text circle.cpp, report.wpd, essay.doc
• Executables circle.exe
• Data readings.dat

11
Disk Format

• A file is made up of many sectors on many tracks
  of the disk.

Track
Disk
Sector
12
System

• The system has a directory that lists files by
  name.
• The system maintains a file allocation table
  (FAT) to associate the filename to the physical
  locations on the disk.
• While a file is active, a file control block
  (FCB) or handle is also active.

13
C and Files

• C allows for the access to files, to store
  (write) data and retrieve (read) data.
• C communicates with the system, allowing for a
  minimum of operations that must be carried out by
  the programmer
• fopen
• read write
• fclose

14
A Simple File Writing Program

• include ltstdio.hgt
• int main()
• FILE fp //FILE type fp is a
• // pointer to a file
• // essentially the FCB
• fpfopen("myfile.txt","w")
• fprintf(fp,"A line in a file\n")
• fclose(fp)
• system("PAUSE") return 0

Lect1501.c
15
fopen, fclose

• fopen returns the pointer to the file or the file
  handle.
• fopen requires the filename and mode
• w write
• r read
• a append, write to the end of the file
• preserving the old contents.
• fclose closes the file pointed to by fp.

16
Append

• fpfopen("myfile.txt","a")
• fprintf(fp,"A second line\n")
• fclose(fp)
• Now the file has two lines
• A line in a file
• A second line
• Using fpfopen("myfile.txt","w")
• would have erased the old contents and the file
  would have just
• A second line

17
ASCII Data File

• include ltstdio.hgt
• int main()
• FILE fp int i
• fpfopen("myfile.txt","w")
• fprintf(fp,"d\n", 23)
• fclose(fp)
• fpfopen("myfile.txt","r")
• fscanf(fp,"d",i)
• fclose(fp)
• printf("d\n",i)
• system("PAUSE") return 0

18
Advantages - Disadvantages

• ADVANTAGE We can read and write an ASCII data
  file with a text editor. It is easy to check.
• DISADVANTAGE Each integer, which takes 2 bytes
  in the regular C data representation, can take up
  to 6 bytes in ASCII (-32768).
• Hence we wish to write in the binary format of C.

19
Binary Data File

• include ltstdio.hgt
• int main()
• FILE fp int i23
• fpfopen("myfile.bin","w")
• fwrite(i, sizeof(int), 1, fp)
• fclose(fp)
• fpfopen("myfile.bin","r")
• fread(i, sizeof(int), 1, fp)
• fclose(fp)
• printf("d\n",i)
• system("PAUSE") return 0

20
fread, fwrite

• The parameter lists for both fread and fwrite are
  the same
• (pointer to variable, size of variable, number of
  variables, file pointer)
• include ltstdio.hgt
• define SIZE 1000
• int main()
• FILE fp int aSIZE
• fpfopen("myfile.bin","w")
• fwrite(a, sizeof(int), SIZE, fp)
• fclose(fp)
• system("PAUSE") return 0

21
Same File Reading and Writing

• include ltstdio.hgt
• define SIZE 10
• int main()
• FILE fp int aSIZE, bSIZE, i
• for(i0 iltSIZE i) aii
• fpfopen("myfile.bin","w")
• fwrite(a, sizeof(int), SIZE, fp)
• rewind(fp)
• fread(b, sizeof(int), SIZE, fp)
• fclose(fp)
• for(i0 iltSIZE i) printf("d ", bi)
• system("PAUSE") return 0

22
rewind and fseek

• rewind gets us to the beginning of the file.
• We can use fseek to move around the file.
• We can use fseek to find our new required
  position
• fseek(FILE stream, long offset,
• int whence)
• SEEK_SET seek from start of file.
• SEEK_CUR seek from current location.
• SEEK_END seek from end of file.

23
whence

• include ltstdio.hgt
• int main()
• FILE fp int i
• fpfopen("myfile.bin","r")
• fseek(fp, sizeof(int)2, SEEK_SET)
• fread(i, sizeof(int), 1, fp)
• fclose(fp)
• printf("d\n", i)
• system("PAUSE") return 0
• i2 fseek passes over the first two integers.

24
Error Checking

• If fopen cannot open a file fopen returns the
  NULL pointer
• if((fpfopen("myfile.txt","r"))NULL)
• printf("File does not exist\n")
• If there are any errors when closing a file,
  fclose returns EOF, else zero
• if(fclose(fp)EOF)
• printf("Errors closing file\n")
• Check the return values on the other functions.

25
Variable Filename

• include ltstdio.hgt
• int main()
• FILE fp char filename20 int i
• printf("Input filename ")
• scanf("s", filename)
• if((fpfopen(filename,"r"))NULL)
• printf("Cannot open file s\n\a", filename)
• else
• fread(i, sizeof(int), 1, fp)
• fclose(fp)
• system("PAUSE") return 0

26
Next File in Sequence

• int main()
• FILE fp char filename20 int i0, error1
• do
• sprintf(filename, "file1d.txt", i)
• if((fpfopen(filename,"r"))!NULL)
  fclose(fp)
• else error0
• while(error1)
• fpfopen(filename,"w")
• printf("Opened file s\n", filename)
• fclose(fp)
• system("PAUSE") return 0