fopen function in c programming with it's example

 fopen c function is used to open a file which is denoted by the file name in c programming.

Syntax for fopen function in c : -

FILE *fopen(const char *filename, const char *mode)

Parameters For for fopen c : -

filename : - this element contain the file name which is going to be open.

Mode :- This string in c contain the method to access the file.

Check the mode for open a file in c programming with the help of fopen c function. 

• "r" Mode : - This mode opens a file for reading.

• "w" Mode : - this one use to create a empty file for writing.

• "a" Mode : - It use to append the data  at the end of the file.
  

• "r+" Mode : - This mode open a file to make an update in reading and writing.

•  "w+" Mode :  - Create an empty file for both reading and writing.

•  "a+" Mode : - Use to open an file for appending and also for reading.
  

Return Value for fopen c function : -

•  fopen function in c return a file pointer otherwise give a null.

• errno global variable is used to indicate the error in fopen function.
  

Example program for fopen function in c :

#include <stdio.h>
#include <stdlib.h>

int main () {
   FILE * fp;

   fp = fopen ("file.txt", "w+");
   fprintf(fp, "%s %s %s %d", "We", "are", "in", 2012);
   
   fclose(fp);
   
   return(0);
}

Example program for fopen c

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Example program for fread function in c

 fread function in c used to read the data from desired file and stored it into a buffer.

syntax For fread c: -

size_t fread(void * buffer, size_t size, size_t count, FILE * stream)

Parameters For fread in c 

fread c use 4 parameters in it's program and these parameters are follow  :- 

Buffer : -  buffer is also know as the space which is used to temporarily stored the data.

it did the same work for fread function in c. 

 Size: This one is an another parameters which is used to read the size in byte for each elements.

Count: Used to count the number of elements (like file for fread in c).

Stream :- Pointer is used for file object to tell the place where data is going to be read.

Return value For fread function in c: -

It return the integer value at the time of success which is equal to the count otherwise error if  value less than count.

Example for the fread c

#include <stdio.h>

int main() {
  char buffer[20]; // Buffer to store data
  FILE * stream;
  stream = fopen("file.txt", "r");
  int count = fread(&buffer, sizeof(char), 20, stream);
  fclose(stream);
  // Printing data to check validity
  printf("Data read from file: %s \n", buffer);
  printf("Elements read: %d", count);
  return 0;
}

OUTPUT

fread c

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Typecast Functions Like atoi in c,atof, itoa, atol more

 atoi in c is used to convert the string data type into int data type.

 atoi function in c

 

Syntax for atoi in c:-

int atoi (const char * str);

 atoi in c function in c is used with the “stdlib.h” header file Well this function is also known as the typecast functions in C.

Example program for the atoi in c

#include <stdio.h>

#include <stdlib.h>
 
int main()
{
    char a[10] = "100";
    int value = atoi(a);
    printf("Value = %d\n", value);
    return 0;
}

Lets check the similar typecast functions Like atoi in c.

atof() function in c  :- atof function work similar like atoi the only difference is atof in c used to converts string data type into float data type.

 Example program for atof() function in c :-

#include <stdio.h>
#include <stdlib.h>
 
int main()
{
    char a[10] = "3.18";
    float pi = atof(a);
    printf("Value of pi = %f\n", pi);
    return 0;
}

 atol() function in c  :-  This function is used to change the string data type to long data type like it's name(atol).

Syntax for atol in c:  -

long int atol ( const char * str );

Example program for atol() function in c :-

#include <stdio.h>
#include <stdlib.h>
 
int main()
{
    char a[20] = "100000000000";
    long value = atol(a);
    printf("Value = %ld\n", value);
    return 0;
}

 itoa() function in c  :- This function is reversed of atoi in c, itoa function is used to convert the int data type to string data type.

Syntax : - 

char *  itoa ( int value, char * str, int base );

Example program for itoa() function in c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
int main()
{
    int a=54325;
    char buffer[20];
    itoa(a,buffer,2);   // 2 means decimal
    printf("Binary value = %s\n", buffer);
 
    itoa(a,buffer,10);   // 10 means decimal
    printf("Decimal value = %s\n", buffer);
 
    itoa(a,buffer,16);   // 16 means Hexadecimal
    printf("Hexadecimal value = %s\n", buffer);
    return 0;
}

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Example Program for memset function in c

 memset() function in C use to take a memory location and taken a VOID* pointer and this function copies the first n byte in memory location.

After update the memory location it return that location with the help of pointer.

memset c

 

Syntax :  -

void* memset(void* mem_loc, int c, size_t n);

mem_loc is a memory location

c is an unsigned character in that upper syntax

Header File for memset function in c

Here this function deal with the characters so we have to use header file in the program

Now the complete import for memset function

#include <string.h>
 
void* memset(void* mem_loc, int c, size_t n);

Program Example for memset c

#include <stdio.h>

#include <string.h>

 
int main() {
    char a[] = {"Hello from functioninc"};
 
    printf("a = %s\n", a);
     
    printf("Filling the first 5 characters a with 'P' using memset\n");
     
    memset(a, 'P', 5 * sizeof(char));
     
    printf("After memset, a = %s\n", a);
 
    return 0;
}

Then the 5 character of the given string is filled by the 'P'

a = Hello from Functioninc
Filling the first 5 characters with 'P' using memset function in c
After memset c, a = PPPPP from Functioninc

Conclusion of memset c

Here we learn about the memset function in c and how to allocate the memory location.

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Understand the extern in c with extern c example

•  extern keyword in C is used when we have multiple source file and we want to shear the variable among those files.

• Or when we prefixing a global variable with the extern keyword in C that's mean we are telling to the compiler that the variable is already defined in other file.

• That's means don't allocate any memory for the same variable twice.
  

What is use of extern in c

extern can be use in two type :-

• A variable declaration statement 

• A variable definition statement 
  

declaration statement for extern

int a;
 
char* ch;

With the help of extern in c we can tell to the compiler that these variables already exist somewhere so don't allocate any memory for these variables.

There is an another way to defining a variable,where you can allocate storage for the given variable. 

// Defining a
int a = 11;
 
// Defining ch, even if it is NULL
char* ch = NULL;

let's check the use of extern in c. You can use this extern keyword only for declaring a global variable.

// Allowed. Variable declaration
extern int a;
 
// Not allowed. extern with variable definition
extern int b = 5;

Let's know about the use of extern in c with example

Assume we have to files 

•     file1x.c, file1x.h

•     file2x.c file2x.h.
  

And a main.c which is an drive program.

Here we have a global variable which is called int file1_var defined in file1x.c.

Here we use extern in extern c example for sharing the same variable for file2x.c.

Here the extern c example : -

// file1.h
// Contains function prototypes for functions of file1.c
 
int addition_1(int a, int b);

// file1.c
// Contains function definition for addition_1()
#include "file1.h"
#include <stdio.h>
 
int file1_var = 100;
 
int addition_1(int a, int b) {
    file1_var = file1_var + 100;
    printf("Inside file1.c addition(). file1_var = %d\n", file1_var);
    return a + b;
}

As you can see that two files share a variable file1_var with the help of extern keyword and this variable will be update when the addition() functions gets called.

Now let's write the main.c program with both the header files file1x.h and file2x.h

#include "file1.h"
#include "file2.h"
#include <stdio.h>
 
// We can also use the file1_var reference here!
extern int file1_var;
 
// We must have only one main() reference
// Since this is our driver program, the main function must be only here
int main() {
    int res1 = addition_1(10, 20);
    int res2 = addition_2(30, 40);
    printf("file1_var = %d\n", file1_var);
    return 0;
}

Output extern c example

Output extern c example

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strtok Fucntion in c with example Program for strtok

•  strtok function in c programming will help you to give the token of given input.
• This kind of function (strtok in c ) is very useful which reduce the length of c program.

 strtok

 

Use of the strtok function in c

strtok is an inbuilt function which is part of the <string.h> c header file.

Let's see first : - 

#include <string.h>
 
char* strtok(char* str, const char* delim);

• This function take an input str and also a delimiter character delim.

• Then strtok() in c split the input string into the tokens which is based on the delimited character.

Return Value of strtok in c

• This function return a single string.

• strtok() in c call this function continuously until we get NULL input sting.

Example for strtok in c

#include <stdio.h>
#include <string.h>
 
int main() {
    // Our input string
    char input_string[] = "Hello from function in c!";
 
    // Our output token list
    char token_list[20][20]; 
 
    // We call strtok(input, delim) to get our first token
    // Notice the double quotes on delim! It is still a char* single character string!
    char* token = strtok(input_string, " ");
 
    int num_tokens = 0; // Index to token list. We will append to the list
 
    while (token != NULL) {
        // Keep getting tokens until we receive NULL from strtok()
        strcpy(token_list[num_tokens], token); // Copy to token list
        num_tokens++;
        token = strtok(NULL, " "); // Get the next token. Notice that input=NULL now!
    }
 
    // Print the list of tokens
    printf("Token List:\n");
    for (int i=0; i < num_tokens; i++) {
        printf("%s\n", token_list[i]);
    }
 
    return 0;
}

We use the strtok(NULL, " ") function in c and use the loop for until the get NULL.

Output strtok in c

Token List:
Hello
from
Function
in
c

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Example program for map() function in python

 map() function in Python applies a given function to every item of an iterable and give a list of results.

Syntax:-

map(function, iterable, ...)

Parameter For map() function in python 

map() function use two Parameter these are follow : - 

•  function is a first Parameter map() function passes every item of iterable to the given function.

• iterables are second which is going to to be mapped.

 Return value : - map() function in python return the list of result.

Example of map() function in python

def calculateSquare(n):
    return n*n


numbers = (1, 2, 3, 4)
result = map(calculateSquare, numbers)
print(result)

# converting map object to set
numbersSquare = set(result)
print(numbersSquare)

OUTPUT : -

 map() function output

Well Python lambda Function commonly used with map () python function.

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