File operations in c

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Target Achieved
1
40
23
2
40
25
3
40
25

4. Jobs Applied
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Company
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Current Status

5. File Operations in c
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6. File management
• Data can be stored on the disk and read whenever necessary, without destroying
the data
• C uses a structure called FILE (defined in stdio.h) to store the attributes of a file.
• FILE- Place on the disk where a group of related data is stored
• C supports a number of functions that have the ability to perform basic file
operations
-Naming a file
-Opening a file
-Reading data from a file
-Writing data to a file
-Closing a file

7. Basic file operations
• C provides several different file operations
• fopen - open a file- specify how its opened (read/write) and type
(binary/text)
• fclose - close an opened file
• fread - read from a file
• fwrite - write to a file
• fseek/fsetpos - move a file pointer to somewhere in a file.
• ftell/fgetpos - tell you where the file pointer is located.

8. Different modes
• Writing mode
– if file already exists then contents are deleted,
– else new file with specified name created
• Appending mode
– if file already exists then file opened with contents safe
– else new file created
• Reading mode
– if file already exists then opened with contents safe
– else error occurs.
• Additional modes
– r+ open to beginning for both reading/writing
– w+ same as w except both for reading and writing
– a+ same as ‘a’ except both for reading and writing

9. Opening a FILE
• Syntax
-FILE *fp; /*variable fp is pointer to type FILE*/
fp = fopen(“filename”, “mode”); /*opens file with name filename , assigns
identifier to fp */
• fp
– contains all information about file
– Communication link between system and program
• The file mode tells C how the program will use the file.
• The filename indicates the system name and location for the file.
• We assign the return value of fopen to our pointer variable:
fp = fopen(“MYFILE.TXT”, “w”);
fp = fopen(“A:MYFILE.TXT”, “w”);

10. Closing a FILE
• When we finish with a mode, we need to close the file before ending the program or
beginning another mode with that same file.
• To close a file, we use fclose and the pointer variable:
fclose(spData);
• Example:
FILE *p1;
p1 = fopen(“INPUT.txt”, “r”);
……..
……..
fclose(p1);
• pointer can be reused after closing

11. Input/output operations on FILES
•
•
•
•
•
•
•
C provides several different functions for reading/writing
getc() – read a character
putc() – write a character
fprintf() – write set of data values
fscanf() – read set of data values
getw() – read integer
putw() – write integer

12. getc() & putc()
• handle one character at a time like getchar() and putchar()
• syntax: putc(c,fp1);
– c : a character variable
– fp1 : pointer to file opened with mode w
• syntax: c = getc(fp2);
– c : a character variable
– fp2 : pointer to file opened with mode r
• file pointer moves by one character position after every getc() and putc()
• getc() returns end-of-file marker EOF when file end reached

13. Program to read/write using getc() & putc()
•
#include <stdio.h>
main()
{
FILE *fp1;
char c;
f1= fopen(“INPUT”, “w”);
while((c=getchar()) != EOF)
putc(c,f1);
fclose(f1);
f1=fopen(“INPUT”, “r”);
while((c=getc(f1))!=EOF)
printf(“%c”, c);
fclose(f1);
} /*end main */
/* open file for writing */
/*get char from keyboard until CTL-Z*/
/*write a character to INPUT */
/* close INPUT */
/* reopen file */
/*read character from file INPUT*/
/* print character to screen */

14. fprintf() & fscanf
• similar to scanf() and printf()
• Syntax:- fprintf()
fprintf (fp,"string",variables);
Example:
int i = 12;
float x = 2.356;
char ch = 's';
FILE *fp;
fp=fopen(“out.txt”,”w”);
fprintf (fp, "%d %f %c", i, x, ch);
• Syntax:- fscanf()
fscanf (fp,"string",identifiers);
Example:
FILE *fp;
Fp=fopen(“input.txt”,”r”);
int i;
fscanf (fp,“%d",i);
• fscanf() returns EOF when end-of file
reached

15. getw() & putw()
• handle one integer at a time
• syntax: putw(i,fp1);
– i : an integer variable
– fp1 : pointer to file ipened with mode w
• syntax: i = getw(fp2);
– i : an integer variable
– fp2 : pointer to file opened with mode r
• file pointer moves by one integer position, data stored in binary format native
to local system
• getw() returns end-of-file marker EOF when file end reached

16. fread()
• Declaration:- fread(void *ptr, size, n, FILE *stream);
• Remarks:
fread reads a specified number of equal-sized data items from an input stream into a block.
– ptr = Points to a block into which data is read
– size = Length of each item read, in bytes
– n = Number of items read
– stream = file pointer
• Example
char a[10]={'1','2','3','4','5','6','7','8','9','a'};
FILE *fs;
fs=fopen("Project.txt","w");
fwrite(a,1,10,fs);
fclose(fs)

17. fwrite()
• Declaration:
fwrite(const void *ptr, size, n, FILE*stream);
• Remarks:
fwrite appends a specified number of equal-sized data items to an output file.
– ptr = Pointer to any object; the data written begins at ptr
– size = Length of each item of data
– n =Number of data items to be appended
– stream = file pointer
• Example
char a[10]={'1','2','3','4','5','6','7','8','9','a'};
FILE *fs;
fs=fopen("Project.txt","w");
fwrite(a,1,10,fs);
fclose(fs);

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