Reading From File C++ Where to Save File

C File management

A File tin can be used to store a large volume of persistent data. Similar many other languages 'C' provides following file management functions,

1. Creation of a file
2. Opening a file
3. Reading a file
4. Writing to a file
5. Closing a file

Following are the most important file direction functions available in 'C,'

function	purpose
fopen ()	Creating a file or opening an existing file
fclose ()	Closing a file
fprintf ()	Writing a block of information to a file
fscanf ()	Reading a block data from a file
getc ()	Reads a single character from a file
putc ()	Writes a unmarried grapheme to a file
getw ()	Reads an integer from a file
putw ()	Writing an integer to a file
fseek ()	Sets the position of a file pointer to a specified location
ftell ()	Returns the current position of a file pointer
rewind ()	Sets the file pointer at the beginning of a file

In this tutorial, you lot will learn-

• How to Create a File
• How to Close a file:
• Writing to a File
• fputc() Part:
• fputs () Office:
• fprintf()Function:
• Reading data from a File
• Interactive File Read and Write with getc and putc

How to Create a File

Whenever yous want to work with a file, the first footstep is to create a file. A file is nothing just space in a memory where data is stored.

To create a file in a 'C' program following syntax is used,

FILE *fp; fp = fopen ("file_name", "manner");          

In the above syntax, the file is a data construction which is defined in the standard library.

fopen is a standard part which is used to open a file.

• If the file is not present on the organization, and then it is created and so opened.
• If a file is already present on the system, then information technology is directly opened using this office.

fp is a file pointer which points to the type file.

Whenever you open or create a file, you have to specify what yous are going to do with the file. A file in 'C' programming can be created or opened for reading/writing purposes. A mode is used to specify whether you desire to open a file for any of the below-given purposes. Following are the different types of modes in 'C' programming which can be used while working with a file.

File Manner	Description
r	Open a file for reading. If a file is in reading style, and then no data is deleted if a file is already present on a system.
w	Open a file for writing. If a file is in writing mode, so a new file is created if a file doesn't exist at all. If a file is already present on a system, so all the information inside the file is truncated, and it is opened for writing purposes.
a	Open a file in append manner. If a file is in append fashion, then the file is opened. The content within the file doesn't change.
r+	open for reading and writing from beginning
westward+	open for reading and writing, overwriting a file
a+	open for reading and writing, appending to file

In the given syntax, the filename and the mode are specified equally strings hence they must always be enclosed within double quotes.

Instance:

#include <stdio.h> int main() { FILE *fp; fp  = fopen ("data.txt", "w"); }          

Output:

File is created in the aforementioned binder where y'all have saved your lawmaking.

You can specify the path where yous want to create your file

#include <stdio.h> int main() { FILE *fp; fp  = fopen ("D://data.txt", "w"); }

How to Close a file

One should always close a file whenever the operations on file are over. It ways the contents and links to the file are terminated. This prevents accidental damage to the file.

'C' provides the fclose function to perform file closing operation. The syntax of fclose is as follows,

fclose (file_pointer);          

Example:

FILE *fp; fp  = fopen ("data.txt", "r"); fclose (fp);          

The fclose office takes a file pointer as an argument. The file associated with the file pointer is so closed with the help of fclose function. It returns 0 if close was successful and EOF (end of file) if there is an error has occurred while file endmost.

Afterward endmost the file, the same file arrow tin besides be used with other files.

In 'C' programming, files are automatically close when the program is terminated. Endmost a file manually by writing fclose office is a good programming practice.

Writing to a File

In C, when y'all write to a file, newline characters '\n' must be explicitly added.

The stdio library offers the necessary functions to write to a file:

• fputc(char, file_pointer): It writes a character to the file pointed to by file_pointer.
• fputs(str, file_pointer): It writes a string to the file pointed to by file_pointer.
• fprintf(file_pointer, str, variable_lists): Information technology prints a string to the file pointed to by file_pointer. The string can optionally include format specifiers and a list of variables variable_lists.

The program below shows how to perform writing to a file:

fputc() Part:

#include <stdio.h> int main() {         int i;         FILE * fptr;         char fn[fifty];         char str[] = "Guru99 Rocks\n";         fptr = fopen("fputc_test.txt", "w"); // "w" defines "writing style"         for (i = 0; str[i] != '\n'; i++) {             /* write to file using fputc() function */             fputc(str[i], fptr);         }         fclose(fptr);         return 0;     }

Output:

The in a higher place program writes a unmarried graphic symbol into the fputc_test.txt file until it reaches the next line symbol "\n" which indicates that the sentence was successfully written. The process is to have each character of the assortment and write information technology into the file.

1. In the higher up program, we have created and opened a file called fputc_test.txt in a write mode and declare our string which will be written into the file.
2. Nosotros do a character past character write operation using for loop and put each character in our file until the "\n" character is encountered then the file is closed using the fclose role.

fputs () Function:

#include <stdio.h> int main() {         FILE * fp;         fp = fopen("fputs_test.txt", "w+");         fputs("This is Guru99 Tutorial on fputs,", fp);         fputs("We don't need to use for loop\n", fp);         fputs("Easier than fputc function\north", fp);         fclose(fp);         return (0);     }

OUTPUT:

1. In the above program, we have created and opened a file called fputs_test.txt in a write way.
2. After we do a write operation using fputs() function by writing three different strings
3. Then the file is closed using the fclose function.

fprintf()Part:

#include <stdio.h>     int main() {         FILE *fptr;         fptr = fopen("fprintf_test.txt", "w"); // "w" defines "writing mode"         /* write to file */         fprintf(fptr, "Learning C with Guru99\n");         fclose(fptr);         return 0;     }

OUTPUT:

1. In the above plan we have created and opened a file called fprintf_test.txt in a write mode.
2. Later a write operation is performed using fprintf() function by writing a cord, then the file is airtight using the fclose function.

Reading data from a File

In that location are three unlike functions dedicated to reading data from a file

• fgetc(file_pointer): It returns the next character from the file pointed to by the file pointer. When the end of the file has been reached, the EOF is sent back.
• fgets(buffer, n, file_pointer): It reads n-ane characters from the file and stores the string in a buffer in which the NULL character '\0' is appended as the last character.
• fscanf(file_pointer, conversion_specifiers, variable_adresses): Information technology is used to parse and analyze information. Information technology reads characters from the file and assigns the input to a list of variable pointers variable_adresses using conversion specifiers. Keep in mind that equally with scanf, fscanf stops reading a cord when space or newline is encountered.

The following program demonstrates reading from fputs_test.txt file using fgets(),fscanf() and fgetc () functions respectively :

#include <stdio.h> int main() {         FILE * file_pointer;         char buffer[30], c;          file_pointer = fopen("fprintf_test.txt", "r");         printf("----read a line----\n");         fgets(buffer, fifty, file_pointer);         printf("%southward\n", buffer);          printf("----read and parse data----\northward");         file_pointer = fopen("fprintf_test.txt", "r"); //reset the pointer         char str1[10], str2[2], str3[twenty], str4[2];         fscanf(file_pointer, "%south %south %due south %s", str1, str2, str3, str4);         printf("Read String1 |%s|\northward", str1);         printf("Read String2 |%s|\n", str2);         printf("Read String3 |%due south|\northward", str3);         printf("Read String4 |%southward|\n", str4);          printf("----read the entire file----\n");          file_pointer = fopen("fprintf_test.txt", "r"); //reset the arrow         while ((c = getc(file_pointer)) != EOF) printf("%c", c);          fclose(file_pointer);         return 0;     }

Result:

----read a line---- Learning C with Guru99  ----read and parse data---- Read String1 |Learning| Read String2 |C| Read String3 |with| Read String4 |Guru99| ----read the entire file---- Learning C with Guru99

1. In the above program, we accept opened the file called "fprintf_test.txt" which was previously written using fprintf() role, and it contains "Learning C with Guru99" string. We read information technology using the fgets() part which reads line by line where the buffer size must exist plenty to handle the entire line.
2. Nosotros reopen the file to reset the arrow file to point at the beginning of the file. Create various strings variables to handle each word separately. Impress the variables to see their contents. The fscanf() is mainly used to extract and parse data from a file.
3. Reopen the file to reset the pointer file to point at the beginning of the file. Read data and print information technology from the file character past grapheme using getc() function until the EOF statement is encountered
4. After performing a reading operation file using dissimilar variants, nosotros again closed the file using the fclose function.

Interactive File Read and Write with getc and putc

These are the simplest file operations. Getc stands for get character, and putc stands for put grapheme. These 2 functions are used to handle only a single grapheme at a fourth dimension.

Following plan demonstrates the file treatment functions in 'C' programming:

#include <stdio.h> int primary() {         FILE * fp;         char c;         printf("File Handling\northward");         //open up a file         fp = fopen("demo.txt", "w");         //writing operation         while ((c = getchar()) != EOF) {             putc(c, fp);         }         //close file         fclose(fp);         printf("Data Entered:\north");         //reading         fp = fopen("demo.txt", "r");         while ((c = getc(fp)) != EOF) {             printf("%c", c);         }         fclose(fp);         return 0;     }          

Output:

1. In the above plan nosotros have created and opened a file called demo in a write style.
2. After a write functioning is performed, then the file is closed using the fclose role.
3. We have once again opened a file which at present contains data in a reading mode. A while loop will execute until the eof is found. One time the finish of file is found the performance volition be terminated and data will be displayed using printf function.
4. Later performing a reading functioning file is again closed using the fclose function.

Summary

• A file is a space in a retention where information is stored.
• 'C' programming provides various functions to deal with a file.
• A mechanism of manipulating with the files is called as file management.
• A file must be opened before performing operations on information technology.
• A file tin exist opened in a read, write or an append mode.
• Getc and putc functions are used to read and write a single grapheme.
• The function fscanf() permits to read and parse data from a file
• We can read (using the getc function) an entire file by looping to embrace all the file until the EOF is encountered
• We can write to a file after creating its proper noun, past using the function fprintf() and it must have the newline character at the stop of the cord text.

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Source: https://www.guru99.com/c-file-input-output.html

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