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What is fgets in C language

Introduction:

A function called fgets within the programming language C reads a certain number of characters into an array of characters from a file stream source. File get string is referred to as fgets. The C language standard library header file, stdio.h, contains it.”

The “file get string” (fgets()) method is commonly employed to read the input string from standard input (stdin) or a file stream. It offers a more secure replacement for the presently deprecated gets() method, which was useful, but now it is unsafe. The fgets() method efficiently handles newline characters and provides a way to limit the amount of characters read.

When a new line character is detected, the file ends, or (length - 1) characters were successfully read, the function stops reading. A new line is appended to the string as being the final character preceding the null character if one has been reached. The space required for the null character, which will be added at the end of the specified string, is included in the length parameter. Consequently, the length parameter needs to be provided as N+1 in order to read N characters. If a minimum of one character has been read and there was no error, the string read is returned; if not, a NULL-pointer will be returned.

Managing input and output tasks is crucial for C programming. Among the several functions that accept input is fgets(). This feature is strong enough to allow developers to read data from a stream accurately and securely. This article will cover the syntax, usage, sample code, as well as expected results of fgets() as we explore its ins and outs.

What is the function fgets() in C language

The C predetermined function fgets() is located inside the stdlib.h header file, which is utilized to read text or strings up to n number of characters from a given file or console and save the data into the designated string variable. It reads the character inputs repeatedly until one of the two conditions listed below is achieved:

  • The stream has been read for (n-1) characters.
  • A new line character appeared.
  • The file's endpoint has been reached.

However, the method fgets() appends a newline character at the final position of the given string variable even though it stops accepting input once that character is detected.

Syntax for fgets() in C language:

fgets(char *string, int number, FILE *stream)

Parameters

From the syntax described above, we have

  1. char *string: A pointer to the character array that will hold the read values
  2. int number: The maximum character count that may be read.
  3. FILE *stream: A pointer towards the file stream whereby the input will be received (when receiving input via the standard input, such as the console, it can be substituted with stdin).

Return Value

  • The pointer string, from where the input is stored, is what the fgets() function is going to return if the reading process is successful.
  • There are a few possible reasons why the fgets() method could return the null pointer in the event that the operation failed. For instance, if the method fgets() encounters an error while its reading operation or reaches the last line of the file before reading any characters, it is going to return a null pointer.
  • It signifies a domain error when the passed parameter of number, or the maximum possible amount of characters that can be read, is less than or it is equal to 0.
  • It will also be valid if the numerical value of the number has been specified as 1. However, keep in mind that it only stores the null terminator because there is only space for one character, and this character will serve as the null terminator. This indicates that no data is going to be read through the given stream.

Examples of function fgets() in C language:

1. Utilizing the function fgets() in C language to read from the console:

#include <stdio.h>

int main()

{

   char string [25];

   printf("Enter the input string : ");

   fgets(string, 25, stdin);

   printf("The given string is : %s", string);

   return 0;

}

Output:

What is fgets in C language

Explanation:

  • We are requesting the programmer to enter the input string into a 25-character char array.
  • Subsequently, we are obtaining user input through the use of the method fgets(). The characters string, 25 and stdin indicate that the input source belongs to the console or, to put it simply, that the user's keyboard should be used to enter text.

2. Reading Data from the File in C through the fgets() Function:

#include <stdio.h>

int main()

{

   char string [25];

   FILE *filepointer;

   filepointer = fopen ("input file.txt", "r");

   if (filepointer == NULL)

   {

      printf ("A mistake happened, and the file could not be read");

   }

   else

   {

      fgets (string, 25, filepointer);

      printf ("The string read from the input file is : %s", str);

   }

   fclose (filepointer);

   return 0;

}

Input data in the file:

Hello World

Hello World

Output:

What is fgets in C language

Explanation:

  • A 20-byte char array has been declared.
  • Next, we open the designated file in read mode and read its contents after defining a file pointer to maintain track of the file that we're viewing.
  • Whenever an error happens, and then the file accessing was unsuccessful, the method fopen() would often returns a null pointer. In this example, we are testing to see whether the file opening failed and, if so, outputting the error message.
  • The function fgets() will be executed if the file opening process succeeds in reading the contents from the file and then storing it in the char array string which has been specified. In this case, str denotes the char array in which the read data would be stored, 20 indicates that the maximum number of 25 characters can be read, and filepointer denotes the source from which the data must be read.
  • Ultimately, we'll be employing the fclose() method to finish our open file; this is optional, but it's often suggested.
  • The reason it only took in “Hello World” and ignored the second line, "Hello World," is because the method fgets(), as we all know, stops accepting input once a new line is detected.

3. Reading Several Lines in C employing the fgets() Function and Stdin:

#include <stdio.h>

#include <string.h>

int main()

{

   char string[500] = "";

   char a[30];

   printf("Enter the input string, press x to exit : ");

   while (fgets(temporary, 30, stdin))

   {

      if (a[0] == 'x' && a[1] == '\n')

      {

          break;

      }

      strcat(string, a);

   }

   printf("The entered string is : %s", string);

   return 0;

}

Output:

What is fgets in C language

Explanation:

  • Here, we'll be utilizing a loop to read several lines over stdin, as contrasted with above, where we simply read one line.
  • First, we create a temporary array that holds the programmers input during each iteration through the loop after initiating an array of characters of size 500 through an empty string.
  • Next, we get input from the user and then store it in the temporary array. Next, we check to see if the user entered the character x; if so, the loop will be terminated.
  • If not, the temporary array is being concatenated into the main string array.
  • Printing the string at the end.

4. Reading the entire File in C with the help of a Loop and the fgets() Function:

#include <stdio.h>

int main()

{

   char string[100];

   FILE *filepointer;

   filepointer = fopen("input file.txt", "r");

   if (filepointer == NULL)

   {

      printf("A mistake happened, and the file could not be read");

   }

   else

   {

      while (fgets(string, 100, filepointer))

      {

          printf("The string read from the file is : %s", string);

      }

   }

   fclose(filepointer);

   return 0;

}

Output:

What is fgets in C language

Explanation:

  • A 100-byte char array is being declared.
  • Next, we open the designated file in read mode to read its contents after defining a file pointer to maintain track of the file we are viewing.
  • whether an error popped up and if the file accessing was unsuccessful, the method fopen() would often return a null pointer. In this example, we are testing to see whether the file opening was failed then it will be outputting the error message.
  • And if the file opening process is successful, we will enter a loop in which we will read the information in the file line by line by employing the function gets() and store it into the char array that has been specified. In this case, string denotes the character array in which the read data is going to be stored, 100 denotes that a maximum of 100 characters are allowed to be read, and filepointer denotes the source from which the data must be read.
  • When the file reaches its end point, the loop will terminate.
  • Ultimately, we are utilizing the fclose() method to terminate the file we have opened; this is not required, but it is advised.

Conclusion:

The fgets() method allows you to read data from files or stdin, including strings or text lines that are not more than n number of  characters length. fgets(char *string, int n,umber FILE *stream) is the syntax. The method fgets() reads the input until it reaches the completion of the file, or a new line is found, or (n-1) characters were successfully read over the stream (where n is the total number of characters to copy). The method fgets() returns a null pointer within the event that the reading operation has been failed, else it returns the pointer to string itself.