Programming C- File Handling , File Operation

Programming C
File Handling in C

File
Handling
• File handling is the process in which we create,
open, read, write, and close operations on a
file.
• Programs are written to store and retrieve the
information from file.
• The data stored in the file can be accessed,
updated, and deleted anywhere and anytime
providing high reusability.
• Portable - Without losing any data, files can
be transferred to another in the computer
system
• Storage - Files allow you to store a large
amount of data and easily access whole or
part of files.

Types of
Files - TEXT
A text file contains data in the form of
ASCII characters and is generally used
to store a stream of characters.
 Each line in a text file ends with a new
line character (‘n’).
 It can be read or written by any text
editor.
 They are generally stored with .txt file
extension.
 Text files can also be used to store the
source code.

Types of Files
- BINARY
A binary file contains data
in binary form (i.e. 0’s and
1’s) instead of ASCII characters.
 The binary files can be created
only from within a program and
their contents can only be
read by a program.
 More secure as they are not
easily readable.
 They are generally stored
with .bin file extension.

File
Operations
• fopen() – To open existing file or create
new file with attributes likes “a” or “a+”
or “w” or “w+”.
• fopen() – To open existing file for
reading with attributes likes “r” or “r+”
• fscanf() or fgets() – To read data from
opened file.
• fprintf() or fputs() – To write data to
opened file.
• fseek(), rewind() – To move
(cursor/pointer) to specific location in a
file.
• fclose() – To close the opened file.

Opening a
file
•FILE* pointername;
•FILE* fopen(const chat
*filename,
• const chat
*accessmode )
• Filename – Name of the file
present in the same directory
as the source program or full
path.
• Accessmode – Indicates the
operations (read, write etc.) for
which file to be opened.
• Returns file pointer if file is
opened successfully, if not
NULL.
•#include <stdlib.h>
•int main()
•{
• FILE* fptr;
• fptr =
fopen("filename.txt", "r");
• if (fptr == NULL) {
• printf("The file is not
opened");
• exit(0);
• }
• return 0;
•}

File Modes - TEXT
Opening
Modes
Description
r
If the file is found and opened successfully, fopen( ) loads it into memory and sets up a
pointer that points to the first character in it. If the file cannot be opened fopen( ) returns
NULL.
w
Open for writing in text mode. If the file exists, its contents are overwritten. If the file
doesn’t exist, a new file is created. Returns NULL, if unable to open the file.
a
If the file is found and opened successfully, fopen( ) loads it into memory and sets up a
pointer that points to the last character in it. It opens only in the append mode. If the file
doesn’t exist, a new file is created. Returns NULL, if unable to open the file.

File Modes – TEXT
Opening
Modes
Description
r+
If the file is found and opened successfully, fopen( ) loads it into memory and sets
up a pointer that points to the first character in it. Returns NULL, if unable to open
the file.
w+
If the file exists, its contents are overwritten. If the file doesn’t exist a new file is
created. Returns NULL, if unable to open the file.
a+
If the file is found and opened successfully, fopen( ) loads it into memory and sets
up a pointer that points to the last character in it. It opens the file in both reading
and append mode. If the file doesn’t exist, a new file is created. Returns NULL, if
unable to open the file.

File Modes - BINARY
Opening
Modes
Description
rb Open for reading in binary mode. If the file does not exist, fopen( ) returns NULL.
wb
Open for writing in binary mode. If the file exists, its contents are overwritten. If
the file does not exist, it will be created.
ab
Open for append in binary mode. Data is added to the end of the file. If the file
does not exist, it will be created.
rb+
Open for both reading and writing in binary mode. If the file does not exist, fopen(
) returns NULL.
wb+
Open for both reading and writing in binary mode. If the file exists, its contents are
overwritten. If the file does not exist, it will be created.
ab+
Open for both reading and appending in binary mode. If the file does not exist, it
will be created.

#include <stdio.h>
#include <stdlib.h>
int main()
{
FILE* fptr;
fptr = fopen("file.txt", "w");
if (fptr == NULL) {
printf("The file is not opened. The program will “);
exit(0);
}
else {
printf("The file is created Successfully.");
}
return 0;
}
Creating a file

The file read operation in C can
be performed using functions
fscanf() or fgets().
Similar to scanf and gets
functions, but fscanf and fgets
have file pointer as parameter.
There are also other functions
we can use to read from a file
Reading from file
fscanf()- Use formatted string and variable
arguments list to take input from a file.
fgets() - Input the whole line from the file.
fgetc() - Reads a single character from the file.
fgetw() - Reads a number from a file.
fread() - Reads the specified amount of bytes
to the binary file.

All file reading functions return
EOF (End Of File) when they
reach the end of the file while
reading.
After reading a particular part
of the file, the file pointer will
be automatically moved to the
end of the last read
character.
Reading from file
FILE * fptr;
fptr = fopen(“fileName.txt”, “r”);
fscanf(fptr, "%s %s %s %d", str1, str2, str3,
&year);
char c = fgetc(fptr);

#include <stdio.h>
#include <string.h>
int main()
{
FILE* filePointer;
char dataToBeRead[50];
filePointer = fopen("Hi.txt", "r");
if (filePointer == NULL) {
printf("Hi.txt file failed to open.");
}
else {
printf("The file is now opened.n");
Reading from TEXT file
while (fgets(dataToBeRead, 50, filePointer)
!= NULL) {
printf("%sn", dataToBeRead);
} //while loop ending
fclose(filePointer);
printf("nData read successfully and file is now closed.");
} //else body ending
return 0;
} //main body ending.

#include <stdio.h>
#include <stdlib.h>
struct threeNum {
int n1, n2, n3;
};
int main()
{
int n;
struct threeNum num;
FILE* fptr;
if ((fptr = fopen("D:program.bin", "rb")) == NULL) {
printf("Error! opening file");
exit(1);
}
Reading from BINARY file
for (n = 1; n < 5; ++n) {
fread(&num, sizeof(struct threeNum), 1,
fptr);
printf("n1: %dtn2: %dtn3: %dn", num.n1,
num.n2,
num.n3);
}
fclose(fptr);
return 0;
}

The file write operations can
be performed by the functions
fprintf() and fputs() with
similarities to read operations.
Writing to a file
fprintf() - Use formatted string and variable
arguments list to print output to the file.
fputs() – Prints the whole line in the file and
new line at the end.
fputc() – Prints a single character into the file.
fputw() – Prints a number to the file.
fwrite() – Writes the specified bytes of data
from a binary file.

#include <stdio.h>
#include <string.h>
int main()
{
FILE* filePointer;
char dataToBeWritten[50] = "Hi welcome to C
progrmming n File Handling nConcepts";
filePointer = fopen("Hi.txt", "w");
//filePointer = fopen("D:Hi.c", "w");
if (filePointer == NULL) {
printf("H.c file failed to open.");
}
Writing to TEXT file
else {
if (strlen(dataToBeWritten) > 0) {
fputs(dataToBeWritten, filePointer);
fputs("n", filePointer);
}
fclose(filePointer);
printf("Data written and file is now closed.");
}
return 0;
}

#include <stdio.h>
#include <stdlib.h>
struct threeNum {
int n1, n2, n3;
};
int main()
{
int n;
struct threeNum num;
FILE* fptr;
if ((fptr = fopen("D:program.bin", "wb")) ==
NULL) {
printf("Error! opening file");
exit(1);
}
Writing to BINARY file
int flag = 0;
for (n = 1; n < 5; ++n) {
num.n1 = n;
num.n2 = 5 * n;
num.n3 = 5 * n + 1;
flag = fwrite(&num, sizeof(struct threeNum), 1,
fptr);
}
if (!flag) {
printf("Write Operation Failure");
}
else {
printf("Write Operation Successful");
} // fclose(fptr); return 0; }

The fclose() function is
used to close the file.
After successful file
operations, close a file to
remove it from the
memory.
Closing a file
FILE *fptr ;
fptr= fopen(“fileName.txt”, “w”);
//perform some operations.
fclose(fptr);

 If file has multiple records and we need to access a particular
record (at a specific position), use fseek() which provides an
easier way to get to the required data.
We use fseek() Instead of looping through all the records before
it to get the record which consumes more memory and
operational time.
fseek() helps to reduce memory consumption and operational
time.
fseek() function in C seeks the cursor to the given record in the
file.
int fseek(FILE *fptr, long int offset, int pos)
Other File Operations - fseek()

 Its used to bring the file
pointer to the beginning of
the file.
It can be used in place of
fseek() when you want the
file pointer at the start or
beginning of the file (BOF).
rewind (file_pointer);
Other File Operations - rewind()
#include <stdio.h>
int main()
{
FILE* fptr;
fptr = fopen("file.txt", "w+");
fprintf(fptr, “Welcome to C Programmingn");
rewind(fptr);
char buf[50];
fscanf(fptr, "%[^n]s", buf);
printf("%s", buf);
return 0;
}

 Its used to find out the
position of the file pointer
in the file with respect to
starting of the file.
long ftell (file_pointer);
Other File Operations - ftell()
#include <stdio.h>
int main()
{
FILE* fp = fopen(“file.txt", "r");
char string[20];
fscanf(fp, "%s", string);
printf("%ld", ftell(fp));
return 0;
}

• Create Student structure
(id,name,mark1,mark2,mark3,total,avg), read Student
details from the user except total and average, calculate the
total & average and write the student structure to file.
• Read the student file in the structure and display each
student details line by line.
• Write program to merge two input files data in to third file
and display the third file content.
Exercises

• The arguments passed from command line are called command line
arguments. These arguments are handled by main() function.
• To support command line argument, programmer needs to change
the structure of main() function as
int main(int argc, char *argv[] )
• Here, argc counts the number of arguments. It counts the file name as
the first argument.
• The argv[] contains the total arguments. The first argument is the file
name always.
Command Line Arguments

#include<stdio.h>
void main(int argc, char *argv[] )
{
printf("Program name is: %sn", argv[0]);
if(argc < 2)
{
printf("No argument passed through command line.n");
}
else
{
printf("First argument is: %sn", argv[1]);
}
}
Example

#include<stdio.h>
#include<stdlib.h>
void main(int argc, char *argv[] )
{
if(argc >= 2)
{
int i=1,sum=0;
while(i <= argc)
{
sum+=atol(argv[i]); //atol Is the function from stdlib.h to convert str to int.
i++;
}
printf("Sum of commandline Arguments are : %dn", sum);
}
}
Example – Sum of digits using CLI

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tutorial
• https://www.tutorialspoint.com/cprogramming/index.htm
• https://www.programiz.com/c-programming
References

Programming C- File Handling , File Operation

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