Learn C Programming

C Language Tutorial
Produced by Ashish Goel
C Programming Language	History of C Language
Features of C Language	How to install C
First C Program	Printf OR Scanf in C
Variables in C	Data Types in C
Keywords in C	C Operators

C Language Control Statement
Produced by Ashish Goel
C if else Statement	C Switch Statement
Loops in C	for loop in C
while loop in C	do while loop in C
C break statement	C continue statement

Function in C Language
Produced by Ashish Goel
Functions in C	Call by value C
Recursion in C	Call by reference in C

Array in C Language
Produced by Ashish Goel
C Array	Two Dimensional Array in C
Passing Array to Function in C

Pointer in C Language
Produced by Ashish Goel
Pointers in C	C Pointer to Pointer
Pointer Arithmetic in C	Dynamic memory allocation in C

Structure and Union in C Language
Produced by Ashish Goel
Structure in C	Nested Structure in C
Union in C Language	File Handling in C

File Handling in C

File Handling in C

File Handling in c language is used to open, read, write, search or close file. It is used for permanent storage.

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Advantage of File

It will contain the data even after program exit. Normally we use variable or array to store data, but data is lost after program exit. Variables and arrays are non-permanent storage medium whereas file is permanent storage medium.

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Functions for file handling

There are many functions in C library to open, read, write, search and close file. A list of file functions are given below:

No.	Function	Description
1	fopen()	opens new or existing file
2	fprintf()	write data into file
3	fscanf()	reads data from file
4	fputc()	writes a character into file
5	fgetc()	reads a character from file
6	fclose()	closes the file
7	fseek()	sets the file pointer to given position
8	fputw()	writes an integer to file
9	fgetw()	reads an integer from file
10	ftell()	returns current position
11	rewind()	sets the file pointer to the beginning of the file

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Opening File

The fopen() function is used to open a file. The syntax of fopen() function is given below:

1. FILE *fopen( const char * filename, const char * mode );  

You can use one of the following modes in the fopen() function.

Mode	Description
r	opens a text file in read mode
w	opens a text file in write mode
a	opens a text file in append mode
r+	opens a text file in read and write mode
w+	opens a text file in read and write mode
a+	opens a text file in read and write mode
rb	opens a binary file in read mode
wb	opens a binary file in write mode
ab	opens a binary file in append mode
rb+	opens a binary file in read and write mode
wb+	opens a binary file in read and write mode
ab+	opens a binary file in read and write mode

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Closing File

The fclose() function is used to close a file. The syntax of fclose() function is given below:

1. int fclose( FILE *fp );  

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Writing File : fprintf() function

The fprintf() function is used to write set of characters into file.

1. #include <stdio.h>  
2. main(){  
3.    FILE *fp;  
4.    fp = fopen("file.txt", "w");//opening file  
5.    fprintf(fp, "Hello file by fprintf...\n");//writing data into file  
6.    fclose(fp);//closing file  
7. }  

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Readiing File : fscanf() function

The fscanf() function is used to read set of characters from file.

1. #include <stdio.h>  
2. main(){  
3.    FILE *fp;  
4.    char buff[255];//creating char array to store data of file  
5.    fp = fopen("file.txt", "r");  
6.    fscanf(fp, "%s", buff);//reading data of file and writing into char array  
7.    printf("Data is : %s\n", buff );//printing data of char array  
8.    fclose(fp);  
9. }  

Output:

Data is : Hello file by fprintf...

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Storing employee information in file

Let's see a file handling example to store employee information as entered by user from console. We are going to store id, name and salary of the employee.

1. #include <stdio.h>  
2. void main()  
3. {  
4.     FILE *fptr;  
5.     int id;  
6.     char name[30];  
7.     float salary;  
8.     fptr = fopen("emp.txt", "w+");/*  open for writing */  
9.     if (fptr == NULL)  
10.     {  
11.         printf("File does not exists \n");  
12.         return;  
13.     }  
14.     printf("Enter the id\n");  
15.     scanf("%d", &id);  
16.     fprintf(fptr, "Id= %d\n", id);  
17.     printf("Enter the name \n");  
18.     scanf("%s", name);  
19.     fprintf(fptr, "Name= %s\n", name);  
20.     printf("Enter the salary\n");  
21.     scanf("%f", &salary);  
22.     fprintf(fptr, "Salary= %.2f\n", salary);  
23.     fclose(fptr);  
24. }  

Output:

Enter the id 
1

Enter the name 
sonoo

120000 

Enter the salary

Now open file from current directory. For window go to TC\bin directory, you will see emp.txt file. It will have following information.

emp.txt

Id= 1

Name= sonoo

Salary= 120000 

Union in C Language

C Union

Like structure, Union in c language is a user defined datatype that is used to hold different type of elements.

But it doesn't occupy sum of all members size. It occupies the memory of largest member only. It shares memory of largest member.

Advantage of union over structure

It occupies less memory because it occupies the memory of largest member only.

Disadvantage of union over structure

It can store data in one member only.

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Defining union

The union keyword is used to define union. Let's see the syntax to define union in c.

1. union union_name   
2. {  
3.     data_type member1;  
4.     data_type member2;  
5.     .  
6.     .  
7.     data_type memeberN;  
8. };  

Let's see the example to define union for employee in c.

1. union employee  
2. {   int id;  
3.     char name[50];  
4.     float salary;  
5. };  

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C Union example

Let's see a simple example of union in C language.

1. #include <stdio.h>  
2. #include <string.h>  
3. union employee    
4. {   int id;    
5.     char name[50];    
6. }e1;  //declaring e1 variable for union  
7. int main( )  
8. {  
9.    //store first employee information  
10.    e1.id=101;  
11.    strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array  
12.    //printing first employee information  
13.    printf( "employee 1 id : %d\n", e1.id);  
14.    printf( "employee 1 name : %s\n", e1.name);  
15.    return 0;  
16. }  

Output:

employee 1 id : 1869508435

employee 1 name : Sonoo Jaiswal

As you can see, id gets garbage value because name has large memory size. So only name will have actual value.

Nested Structure in C

Nested structure in c language can have another structure as a member. There are two ways to define nested structure in c language:

1. By separate structure
2. By Embedded structure

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1) Separate structure

We can create 2 structures, but dependent structure should be used inside the main structure as a member. Let's see the code of nested structure.

1. struct Date  
2. {  
3.    int dd;  
4.    int mm;  
5.    int yyyy;   
6. };  
7. struct Employee  
8. {     
9.    int id;  
10.    char name[20];  
11.    struct Date doj;  
12. }emp1;  

As you can see, doj (date of joining) is the variable of type Date. Here doj is used as a member in Employee structure. In this way, we can use Date structure in many structures.

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2) Embedded structure

We can define structure within the structure also. It requires less code than previous way. But it can't be used in many structures.

1. struct Employee  
2. {     
3.    int id;  
4.    char name[20];  
5.    struct Date  
6.     {  
7.       int dd;  
8.       int mm;  
9.       int yyyy;   
10.     }doj;  
11. }emp1;  

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Accessing Nested Structure

We can access the member of nested structure by Outer_Structure.Nested_Structure.member as given below:

1. e1.doj.dd  
2. e1.doj.mm  
3. e1.doj.yyyy  

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C Nested Structure example

Let's see a simple example of nested structure in C language.

1. #include <stdio.h>  
2. #include <string.h>  
3. struct Employee  
4. {     
5.    int id;  
6.    char name[20];  
7.    struct Date  
8.     {  
9.       int dd;  
10.       int mm;  
11.       int yyyy;   
12.     }doj;  
13. }e1;  
14. int main( )  
15. {  
16.    //storing employee information  
17.    e1.id=101;  
18.    strcpy(e1.name, "Sonoo Jaiswal");//copying string into char array  
19.    e1.doj.dd=10;  
20.    e1.doj.mm=11;  
21.    e1.doj.yyyy=2014;  
22.   
23.    //printing first employee information  
24.    printf( "employee id : %d\n", e1.id);  
25.    printf( "employee name : %s\n", e1.name);  
26.    printf( "employee date of joining (dd/mm/yyyy) : %d/%d/%d\n", e1.doj.dd,e1.doj.mm,e1.doj.yyyy);  
27.    return 0;  
28. }  

Output:

employee id : 101

employee name : Sonoo Jaiswal

employee date of joining (dd/mm/yyyy) : 10/11/2014