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Writing to a File in C Programming
To write on a file there are following function available:
- Function fputc() : function fputc() write individual characters at a time to the file. The syntax of this function is –
Syntax :
int fputc( int c, FILE *fp );
Function fputc() returns the written character written on success and if there is an error it will return EOF (Emd of File).
- Function fputs() : function fputs() writes the string ‘s’ to the output stream referenced by fp. The syntax of this function is –
Syntax :
int fputs( const char *s, FILE *fp );
Function fputs() returns the non-negative value on success and if there is an error it will return EOF (Emd of File).
- Function fprintf(): Function fprintf()write a string into a file. The syntax of this function is –
Syntax :
int fprintf(FILE *fp, const char *format, …)
Example: Write a C program to write a single character into file using fputc() function in file handling.
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#include <stdio.h> int main() { FILE *fp; fp = fopen("c/Book1.txt", "w+"); //opening file Book1.txt for write fprintf(fp, "Hello hii how are you \n"); //write a string into file Book1.txt fputs("I am aditya \n", fp); //write a string into file Book1.txt fclose(fp); //closing file } |
OUTPUT
a
BOOK1.txt
Example: Write a C program to write a string into a file using fputs() and fprintf() function in file handling.
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#include <stdio.h> int main() { FILE *fp; fp = fopen("c/Book1.txt", "w+"); //opening file Book1.txt for write fprintf(fp, "Hello hii how are you \n"); //write a string into file Book1.txt fputs("I am aditya \n", fp); //write a string into file Book1.txt fclose(fp); //closing file } |
OUTPUT
Hello hii how are you
I am aditya
Book1.txt
Description: When we run the above program , it creates a new file Book1.txt in /c directory and writes two lines using fputs() and fprintf() functions.
Example : Write a C program to open a file, write in it and close the file.
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# include <stdio.h> # include <string.h> int main( ) { FILE *fp ; // Declare the file pointer fp char str[30] = "i am aditya from it department"; // data to be written in file fp = fopen("Book1.txt", "w") ; // Open file Book1.txt using for write if ( fp == NULL ) // Check if this filePointer is null { printf( "failed to open file" ) ; } else { printf("The file is now opened.\n") ; if ( strlen ( str ) > 0 ) // check the length of data >0 { fputs(str, fp) ; // writing in the file using fputs() fputs("\n", fp) ; } fclose(fp) ; // closing file printf("The file is now closed.") ; } return 0; } |
OUTPUT
i am aditya from it department
Book1.txt
Reading a File in C Programming
Reading a File
To read a file there are following function available:
- Function fgetc(): Function fgetc() is used to read a single character at a time from the input file. The syntax of this function is −
Syntax :
int fgetc( FILE * fp );
- Functions fgets(): Functions fgets() is used to reads string from input file, one line at a time. The syntax of this function is –
Syntax :
char *fgets( char *buf, int n, FILE *fp );
function fgets() copies the read string into the buffer buf and appending a null character to terminate the string.
Here “n” is a size of buffer.
*fp- is a file pointer.
If the function fgets() encounters a character ‘\n’ ( newline ) or the end of the file ( EOF ) before reading the maximum number of characters, then it will returns the characters read up to that point including the new line character.
- Function fscan(): Function fscan() is also use to read strings from a file. The syntax of this function is –
Syntax :
int fscanf(FILE *fp, const char *format, …)
Note: fscan() function stops reading after encountering the first space character in file.
Closing a File
The fclose() function is used to
close an already opened file. The syntax of this function is −
Syntax :
int fclose( FILE *fp );
Function fclose(-) returns zero if the file is successfully closed, or EOF if there is an error in closing the file.
Example: Write a C program to show the use of fgets() and fscan() function using file handling.
Suppose we have a file Book.txt, that have following content
| Hello hii how are you I am aditya |
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#include <stdio.h> int main() { FILE *fp; char buff[250]; // 250 is a size of buffer fp = fopen("Book.txt", "r"); // open file "book.txt" for reed fscanf(fp, "%s", buff); // read one word and store in buffer printf("\n fscan() function print = %s", buff ); fgets(buff, 250, (FILE*)fp); // read remain line till end of line and store in buffer printf("\n fgets() function print = %s", buff ); fgets(buff, 250, (FILE*)fp); printf("\n fgets() function print = %s", buff ); // read complete one line and store in buffer fclose(fp); // close file "book.txt" } |
OUTPUT
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fscan() function print = Hello fgets() function print = hii how are you fgets() function print = I am aditya |
Description: fscanf() function read only “Hello” because after that, it encountered a space. fscan() function stops reading after encountering the first space character in file.
Function fgets() reads the remaining line till it encountered end of line. fgets() is reads string from input file, one line at a time.
Finally, the last fgets() reads the second line completely.
Example: Write a C program to open a file, read a file and close file using file handling.
Or
Example: Write a program to show the use of fgetc() function.
Note: Used for reads a single character from file. It returns EOF at the end of file.
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#include<stdio.h> void main( ) { FILE *fp; // file pointer char ch; fp = fopen("file1.c","r"); // file1 is name of the file to be open while ( 1 ) // condition is true { //read each character from a file and stored in the character variable ‘ch’. ch = fgetc ( fp ); if ( ch == EOF ) // checking EOF { break; // break & jump outside of loop } printf("%c",ch); } fclose (fp ); } |
OUTPUT
The content of the file “file1” will be printed.
File Handling in C Programming
A file represents a sequence of bytes and these file’s is used to store information. There are various different operations that we can be performed on a file are:
- Creation of a new file (fopen with attributes as “a” or “a+” or “w” or “w++”)
- Opening an existing file (fopen)
- Reading from file (fscanf or fgetc)
- Writing to a file (filePointerrintf or filePointeruts)
- Moving to a specific location in a file (fseek, rewind)
- Closing a file (fclose)
Functions for file handling
There are various predefined functions available for handle file. Some of them mentioned below:
| Function | Description |
|---|---|
| fopen() | Used for opens new or existing file |
| fprintf() | Used for write data into the file |
| fscanf() | Used for reads data from the file |
| fputc() | Used for writes a single character into the file |
| fgetc() | Used for reads a single character from file |
| fclose() | Used for closes the file |
| fseek() | sets the file pointer to given position |
| fputw() | Used for writes an integer to file |
| fgetw() | Used for reads an integer from file |
| ftell() | returns current position |
| rewind() | sets the file pointer to the beginning of the file |
Create or Open Files
We can create a new file or open an existing file by using fopen() function. To create a new file or open an existing file syntax is:
FILE *fopen( const char * filename, const char * mode );
Here, filename is a string literal and use one of the following modes in the fopen() function if you are working with text file:-
| File Mode | Meaning of Mode |
|---|---|
| r | opens a file in read mode. If the file does not exist, fopen() returns NULL. |
| w | opens a file in write mode. If the file does not exist, fopen() returns NULL. |
| a | opens a file in append mode ( Data is added to end of file). f the file does not exists, it will be created. |
| r+ | opens a file in a both read and write mode. If the file does not exist, fopen() returns NULL. |
| w+ | opens a file in both read and write mode. If the file exists, its contents are overwritten. If the file does not exist, it will be created. |
| a+ | opens a file in both read and write mode. If the file does not exists, it will be created. |
Arithmetic Operation With Pointer
In a C programming, we can also perform arithmetic operations with pointer. There are four arithmetic operators that can be performed with pointers:
- Increment (++)
- Decrement ( — )
- Addition ( + )
- Subtraction ( – )
Increment a Pointer
Example: Write a program in c language, to increments the variable pointer to access each succeeding element of the array.
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#include <stdio.h> int main () { int arr[] = {10, 20, 30}; int i, *ptr; ptr = arr; //assign the stsrting array address to pointer variable pointer for ( i = 0; i < 3; i++) { printf("\n Address of arr[%d] = %d", i, ptr ); printf("\n Value of arr[%d] = %d", i, *ptr ); ptr++; // move to the next location } return 0; } |
OUTPUT
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Address of arr[0] = -908782628 Value of arr[0] = 10 Address of arr[1] = -908782624 Value of arr[1] = 20 Address of arr[2] = -908782620 Value of arr[2] = 30 |
Array of pointers in C Programming
Example: Write a program to assign the address of array elements to pointer variable and print the array element with address.
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#include <stdio.h> int main () { int arr[] = {10, 20, 30}; int i, *ptr[3]; for ( i = 0; i < 3; i++) { ptr[i] = &arr[i]; // assign the address array element to pointer variable } for ( i = 0; i < 3; i++) { printf("\n Value of arr[%d] = %d", i, *ptr[i] ); printf("\n Address of arr[%d] = %d", i, ptr[i] ); } return 0; } |
OUTPUT
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Value of arr[0] = 10 Address of arr[0] = 1392582964 Value of arr[1] = 20 Address of arr[1] = 1392582968 Value of arr[2] = 30 Address of arr[2] = 1392582972 |
NULL Pointers in C Programming
A pointer that is assigned NULL is called a null pointer. We must initialize NULL pointer during variable declaration.
A null pointer refers to pointer variable that does not point to a valid address.
Generally NULL pointer is used when you do not have an exact address to be assigned.
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#include <stdio.h> int main () { int *ptr = NULL; printf("The value of ptr is : %d", ptr ); return 0; } |
OUTPUT
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The value of ptr is : 0 |
Pointer to Pointer in C Programming
In C language, a pointer is an address. Normally, a pointer variable contains the address of a another variable.
A pointer to a pointer is a chain of pointers.
Or
Pointer to pointer means one pointer variable holds the address of another pointer variable.
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#include<stdio.h> int main() { int a=4; int *b, **c; b = &a; c = &b; printf("\n Address of a = %d", &a); printf("\n Address of a = %d", b); printf("\n Address of a = %d", *c); printf("\n Address of b = %d", &b); printf("\n Address of b = %d", c); printf("\n Address of c = %d", &c); printf("\n Value of c = %d", c); printf("\n Value of c = %d", *(&c)); printf("\n Value of b = %d", b); printf("\n Value of b = %d", *(&b)); printf("\n Value of b = %d", *c); printf("\n Value of a = %d", a); printf("\n Value of a = %d", *(&a)); printf("\n Value of a = %d", *b); printf("\n Value of a = %d", **c); return 0; } |
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Address of a = 2464 Address of a = 2464 Address of a = 2464 Address of b = 2480 Address of b = 2480 Address of c = 2490 Value of c = 2480 Value of c = 2480 Value of b = 2464 Value of b = 2464 Value of b = 2464 Value of a = 4 Value of a = 4 Value of a = 4 Value of a = 4 |
Pointers in C Programming
In programming, variable is used to hole the value & this variable stored in a memory. Each variable has a address to identify where these variables actually stored in a memory.
In a C programming language, pointer is a variable which can hold the address of another variable.
Accessing Address of Variable
In a system every memory location has its address & we can access the address using ampersand (&) operator.
This ampersand (&) operator denotes an address in memory.
Ex:
int i = 20;
char c = ‘a’;
In the above example, there are two variable i & c.
Integer variable “i” stores the value 10 at memory location 1024(for example) and character variable “c” stores the value ‘a’ at memory location 1026.
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#include<stdio.h> int main() { int i=20; int c='a'; printf("\n value of variable i= %d", i ); printf("\n value of variable c= %c", c ); } |
OUTPUT
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value of variable i= 20 value of variable c= a |
If we want to print the address of variable ‘i and c’ then we need ampersand (&) operator .
#includeOUTPUT
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Address of variable i = 1641813104 Address of variable c= 1641813108 |
Note: When you run this program, address are printed might be different.
Example: Write a program to print the address of the variable.
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#include <stdio.h> int main () { int v1; char v2; float v3; printf("\n Address of variable v1= %d", &v1 ); printf("\n Address of variable v2= %d", &v2 ); printf("\n Address of variable v3= %d", &v3 ); return 0; } |
OUTPUT
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Address of variable v1= 1174657312 Address of variable v2= 1174657313 Address of variable v3= 1174657308 |
Note: Each and every time when you run this program these variables stored in a different memory location.
Pointer Variable
pointer variable is hold the address of another variable.
Declare a pointer variable
To declare a pointer variable, there must use a * (Asterisk) before variable name.
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#include <stdio.h> int main () { int i= 20; // declare & initialize variable i int *ptr; // declare a pointer variable ptr ptr = &i; // ptr (pointer variable) holds the address of variable i. printf("\n Address of variable i= %d", &i ); printf("\n Address of variable i= %d", ptr ); return 0; } |
OUTPUT
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Address of variable i= 511276620 Address of variable i= 511276620 |
Value at address
In the above example, there are two variable, first is normal variable ‘i’ & pointer variable ‘ptr’.
Integer variable “i” stores the value 10 at memory location 1024(for example) and pointer variable “ptr” stores the address of variable ‘i’ at memory location 2322
Example
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#include <stdio.h> int main () { int i= 10; // declare & initialize variable i int *ptr; // declare a pointer variable ptr ptr = &i; // ptr (pointer variable) holds the address of variable i. printf("\n value of variable i= %d", *ptr ); return 0; } |
OUTPUT
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value of variable i= 10 |
Note: Pointer variable “ptr” prints the address of variable and “*ptr” prints the value of i. *variable name (*ptr) is also called value at address.
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#include<stdio.h> int main() { int a=4; int *b; b = &a; printf("\n Address of a = %d", &a); printf("\n Address of a = %d", b); printf("\n Address of b = %d", &b); printf("\n Value of b = %d", b); printf("\n Value of a = %d", a); printf("\n Value of a = %d", *(&a)); printf("\n Value of a = %d", *b); return 0; } |
OUTPUT
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Address of a = 2464 Address of a = 2464 Address of b = 2466 Value of b = 2490 Value of a = 4 Value of a = 4 Value of a = 4 |
Note: When you run this program, address are printed might be different.
Recursion in C Programming
In C programming language, a function that calls itself is known as a recursive function. And, this technique is called as recursion.
Recursive functions are very useful to solve many problems such as Towers of Hanoi (TOH), Inorder/Preorder/Postorder Tree Traversals, DFS of Graph, etc.
How recursion works?
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void recurse() { ... .. ... recurse(); ... .. ... } int main() { ... .. ... recurse(); ... .. ... } |
Example: Write a program in a C language to find the factorial using recursion.
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#include <stdio.h> long int factorial(int n); int main() { int n; printf("Enter a number to find factorial: "); scanf("%d", &n); printf("Factorial of %d = %ld", n, factorial(n)); return 0; } long int factorial(int n) { if (n >= 1) return n*factorial(n-1); else return 1; } |
OUTPUT
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Enter a number to find factorial: Factorial of 5 = 120 |
Example: Write a program in a C language to print the Fibonacci series using recursion.
Fibonacci series are 0, 1, 1, 2, 3, 5, 8, …,.
In fibonacci series, except for the first two terms of the series, every other term is the sum of the previous two terms, for example, 5 = 2 + 3.
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#include<stdio.h> int fibonacci(int); int main() { int n, i = 0, c; printf("Enter the nth number in fibonacci series "); scanf("%d", &n); printf("\n Fibonacci series terms are:\n"); for (c = 1; c <= n; c++) { printf("%d\n", fibonacci(i)); i++; } return 0; } int fibonacci(int n) { if (n == 0 || n == 1) return n; else return (fibonacci(n-1) +fibonacci(n-2)); } |
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Enter the nth number in fibonacci series 10 Fibonacci series terms are: 0 1 1 2 3 5 8 13 21 34 |
Difference between structure and union in C Programming
union occupies less memory than structure
union variable can store one value at a time & same memory location, can be used to store multiple types of data.
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#include<stdio.h> #include <string.h> struct Student_Structure { char name[30]; char section[1]; int rollno; int Class; } s1; union Student_union { char name[30]; char section[1]; int rollno; int Class; } u1; int main() { printf("\n 1st difference is union occupies less memory than structure"); printf("\nsizeof structure : %d\n", sizeof(s1)); printf("sizeof union : %d\n", sizeof(u1)); printf("\n 2nd difference is union variable can store one value at a time & same memory location, can be used to store multiple types of data."); // store student name, rollno, class & section using structure variable s1 strcpy(s1.name, "Aditya"); s1.rollno = 12345; s1.Class = 12; strcpy(s1.section, "A"); printf("\n Student details using structure"); printf("\n Name = %s", s1.name); printf("\n Rollno = %d", s1.rollno); printf("\n Class = %d", s1.Class); printf("\n Section = %s", s1.section); // store student name, rollno, class & section using union variable u1 strcpy(u1.name, "Aditya"); u1.rollno = 12345; u1.Class = 12; strcpy(u1.section, "A"); printf("\n Student details using union"); printf("\n Name = %s", u1.name); printf("\n Rollno = %d", u1.rollno); printf("\n Class = %d", u1.Class); printf("\n Section = %s", u1.section); return 0; } |
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1st difference is union occupies less memory than structure sizeof structure : 40 sizeof union : 32 2nd difference is union variable can store one value at a time & same memory location, can be used to store multiple types of data. Student details using structure Name = Aditya Rollno = 12345 Class = 12 Section = A Student details using union Name = A Rollno = 65 Class = 65 Section = A |