How to Read Into a Text File in C++

C programming language supports iv pre-defined functions to read contents from a file, defined in stdio.h header file:

1. fgetc() – This part is used to read a single character from the file.
2. fgets() – This role is used to read strings from files.
3. fscanf() – This function is used to read the block of raw bytes from files. This is used to read binary files.
4. fread() – This function is used to read formatted input from a file.

Steps To Read A File:

• Open a file using the function fopen() and store the reference of the file in a FILE pointer.
• Read contents of the file using whatever of these functions fgetc(), fgets(), fscanf(), or fread().
• File close the file using the function fclose().

Permit's brainstorm discussing each of these functions in detail.

fgetc()

fgetc() reads characters pointed by the function arrow at that time. On each successful read, it returns the graphic symbol (ASCII value) read from the stream and advances the read position to the next character. This function returns a constant EOF (-1) when there is no content to read or an unsuccessful read.

Syntax:

int fgetc(FILE *ptr);

Approach:

• This program reads the whole content of the file, using this function by reading characters one by one.
• Do-While loop will be used which will read character until it reaches and of file.
• When it reaches end information technology returns  EOF character (-1).

Using EOF:
Below is the C program to implement the above arroyo-

C

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

int main()

{

FILE * ptr;

char ch;

ptr = fopen ( "examination.txt" , "r" );

if (Goose egg == ptr) {

printf ( "file tin't be opened \north" );

}

printf ( "content of this file are \northward" );

practice {

ch = fgetc (ptr);

printf ( "%c" , ch);

} while (ch != EOF);

fclose (ptr);

return 0;

}

Input File:

GeeksforGeeks | A computer science portal for geeks

Output:

In the higher up code, the arroyo is to read one character from the file and check if information technology is not EOF, if it is non then print it and if it is so finish reading.

Using feof():
feof() function takes file pointer every bit argument and returns true if pointer reaches the end of the file.

Syntax:

int feof(FILE *ptr);

Approach:

• In this approach, a character is read using fgetc().
• Using feof() function check for end of file. since feof() returns truthful after it reaches the end.
• Employ logical NOT operator(!) so that when it reaches stop condition become faux and loop terminate.

Below is the C program to implement the above approach:

C

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

int chief()

{

FILE * ptr;

char ch;

ptr = fopen ( "test.txt" , "r" );

if (Zippo == ptr) {

printf ( "file can't exist opened \due north" );

}

printf ( "content of this file are \n" );

while (! feof (ptr)) {

ch = fgetc (ptr);

printf ( "%c" , ch);

}

fclose (ptr);

return 0;

}

Input File:

GeeksforGeeks | A computer science portal for geeks

Output:

fgets()

fgets() reads one string at a time from the file. fgets() returns a cord if it is successfully read by function or returns NULL if can not read.

Syntax:

char * fgets(char *str, int size, FILE * ptr);

Hither,
str: It is cord in which fgets() shop string after reading it from file.
size: It is maximum characters to read from stream.
ptr: It is file pointer.

Approach:

• In this approach, the contents of the file are read i character at a time until we achieve the cease of the file.
• When nosotros reach the end of the file fgets() tin't read and returns NULL and the program will cease reading.

Beneath is the C program to implement the in a higher place approach:

C

#include <stdio.h>

#include <stdlib.h>

#include <cord.h>

int main()

{

FILE * ptr;

char str[fifty];

ptr = fopen ( "exam.txt" , "a+" );

if (Zip == ptr) {

printf ( "file can't exist opened \n" );

}

printf ( "content of this file are \north" );

while ( fgets (str, 50, ptr) != NULL) {

printf ( "%southward" , str);

}

fclose (ptr);

render 0;

}

Input File:

GeeksforGeeks | A computer scientific discipline portal for geeks

Output:

fscanf()

fscanf() reads formatted input from a stream.

Syntax:

int fscanf(FILE *ptr, const char *format, …)

Approach:

• fscanf reads formatted data from the files and stores it in variables.
• The data in the buffer is printed on the panel till the end of the file is reached.

C++

#include <stdio.h>

int master()

{

FILE * ptr = fopen ( "abc.txt" , "r" );

if (ptr == Nothing) {

printf ( "no such file." );

render 0;

}

char buf[100];

while ( fscanf (ptr, "%*s %*south %s " ,

buf)

== 1)

printf ( "%s\n" , buf);

return 0;

}

Output:

fread()

fread() makes information technology easier to read blocks of data from a file. For example, in the case of reading a structure from the file, it becomes an easy job to read using fread.

Syntax:

size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream)

ptr: This is the pointer to a block of memory with a minimum size of size*nmemb bytes.
size: This is the size in bytes of each element to exist read.
nmemb: This is the number of elements, each one with a size of size bytes.
stream: This is the pointer to a FILE object that specifies an input stream.

Arroyo:

• It first, reads the count number of objects, each 1 with a size of size bytes from the given input stream.
• The total amount of bytes reads if successful is (size*count).
• According to the no. of characters read, the indicator file position is incremented.
• If the objects read are non trivially re-create-able, then the behavior is undefined and if the value of size or count is equal to cipher, and so this plan will simply return 0.

C++

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

struct Course {

char cname[xxx];

char sdate[thirty];

};

int chief()

{

FILE * of;

of = fopen ( "test.txt" , "westward" );

if (of == Cypher) {

fprintf (stderr,

"\nError to open the file\n" );

exit (i);

}

struct Class inp1 = { "Algorithms" ,

"30OCT" };

struct Grade inp2 = { "DataStructures" ,

"28SEPT" };

struct Grade inp3 = { "Programming" ,

"1NOV" };

fwrite (&inp1, sizeof ( struct Course),

1, of);

fwrite (&inp2, sizeof ( struct Course),

1, of);

fwrite (&inp3, sizeof ( struct Course),

one, of);

if ( fwrite != 0)

printf ( "Contents to file written successfully !\n" );

else

printf ( "Error writing file !\n" );

fclose (of);

FILE * inf;

struct Grade inp;

inf = fopen ( "examination.txt" , "r" );

if (inf == Null) {

fprintf (stderr,

"\nError to open the file\due north" );

leave (i);

}

while ( fread (&inp, sizeof ( struct Grade),

1, inf))

printf ( "Course Proper noun = %southward Started = %s\n" ,

inp.cname, inp.sdate);

fclose (inf);

}

Output:

johnsonlowent1951.blogspot.com

Source: https://www.geeksforgeeks.org/c-program-to-read-contents-of-whole-file/

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