- A file refers to a disk file, terminal, printer, or tape drive. Data is transferred between a program and file via a stream, which is temporarily stored in a buffer. - To access a file, it must be opened using fopen() and closed with fclose(). Different modes like "r", "w", and "a" determine if the file can be read, written to, or appended to. - Example C code is provided that opens a file for reading and writing, reads/writes characters and lines one at a time between files, and closes the files. Functions like fgetc(), fputc(), fgets(), and fputs() perform the read/write operations.

1. Disk File Input and Output

2. • A file can refer to a disk file, a terminal, a printer, or a tape drive.
• Stream is data flow you transfer from your program to a file, or vice versa.
• buffer is a memory area, which is temporarily used to store data before it is sent to
its destination.
• Step of file
– Opening a File
FILE *fopen(char *filename,char *mode);
– Closing a File
fclose(*pfile);
Note:
• "w" Open text file for write operations. If the file exists, its current contents are
discarded.
• "a" Open a text file for append operations. All writes are to the end of the file.
• "r" Open a text file for read operations.

3. Writing to a Text File

4. Reading from a Text File

5. #include <stdio.h>
#include <string.h>
#include <stdlib.h>
const int LENGTH = 80; /* Maximum input length */
int main(void)
{
char mystr[LENGTH]; /* Input string */
int lstr = 0; /* Length of input string */
int mychar = 0; /* Character for output */
FILE *pfile = NULL; /* File pointer */
char *filename = "C:myfile.txt";
printf("nEnter string of less than 80 characters:n");
fgets(mystr, LENGTH, stdin); /* Read in a string */
/* Create a new file we can write */
if(!(pfile = fopen(filename, "w")))
{
printf("Error %s for writing. ", filename);
exit(1);
}
lstr = strlen(mystr);
for(int i = lstr-1 ; i >= 0 ; i--)
fputc(mystr[i], pfile); /* Write string to file */
fclose(pfile); /* Close the file */
/* Open the file for reading */
if(!(pfile = fopen(filename, "r")))
{
printf("Error opening %s for reading. Program
terminated.", filename);
exit(1);
}
/* Read a character from the file and display it */
while((mychar = fgetc(pfile)) != EOF)
putchar(mychar); /* Output character
from the file */
putchar('n'); /* Write newline
*/
fclose(pfile); /* Close the file
*/
remove(filename); /* Delete the physical
file */
return 0;
}

6. /* 21L02.c: Reading and writing one character at a time */
#include <stdio.h>
enum {SUCCESS, FAIL};
void CharReadWrite(FILE *fin, FILE *fout);
main(void)
{
FILE *fptr1, *fptr2;
char filename1[]= "outhaiku.txt";
char filename2[]= "haiku.txt";
int reval = SUCCESS;
if ((fptr1 = fopen(filename1, "w")) == NULL){
printf("Cannot open %s.n", filename1);
reval = FAIL;
} else if ((fptr2 = fopen(filename2, "r")) == NULL){
printf("Cannot open %s.n", filename2);
reval = FAIL;
} else {
CharReadWrite(fptr2, fptr1);
fclose(fptr1);
fclose(fptr2);
}
return reval;
}
/* function definition */
void CharReadWrite(FILE *fin, FILE
*fout)
{
int c;
while ((c=fgetc(fin)) != EOF){
fputc(c, fout); /* write to a file */
putchar(c); /* put the character
on the screen */
}
}

7. /* 21L03.c: Reading and writing one line at a time */
#include <stdio.h>
enum {SUCCESS, FAIL, MAX_LEN = 81};
void LineReadWrite(FILE *fin, FILE *fout);
main(void)
{
FILE *fptr1, *fptr2;
char filename1[]= "outhaiku.txt";
char filename2[]= "haiku.txt";
int reval = SUCCESS;
if ((fptr1 = fopen(filename1, "w")) == NULL){
printf("Cannot open %s for writing.n", filename1);
reval = FAIL;
} else if ((fptr2 = fopen(filename2, "r")) == NULL){
printf("Cannot open %s for reading.n", filename2);
reval = FAIL;
} else {
LineReadWrite(fptr2, fptr1);
fclose(fptr1);
fclose(fptr2);
}
return reval;
}
/* function definition */
void LineReadWrite(FILE *fin, FILE *fout)
{
char buff[MAX_LEN];
while (fgets(buff, MAX_LEN, fin) !=
NULL){
fputs(buff, fout);
printf("%s", buff);
}
}