C Programming: File I/O Basics

Questions and Answers

What does the mode 'a' signify when opening a file in C?

Open the file in binary format

Write to the file and truncate it

Append data to the end of the file (correct)

Read from the file

Which function is used to close an open file in C?

fclose() (correct)

closefile()

endfile()

file_close()

What does the function fscanf() do?

Reads formatted input from a file (correct)

Writes formatted output to a file

Reads an entire line from a file

Reads a single character from a file

What should you check after opening a file to ensure it was successful?

The file pointer is not NULL Signup and view all the answers

Which of the following functions can be used to write a single character to a file?

fputc() Signup and view all the answers

Which function should be used to read a whole line from a file?

fgets() Signup and view all the answers

What mode should you use if you want to read a binary file in C?

rb Signup and view all the answers

What is the return type of the fclose() function?

int Signup and view all the answers

Which of the following is true about the 'w' mode when opening a file?

It creates a new file or truncates an existing one. Signup and view all the answers

Which function can be utilized for writing an entire string to a file?

fputs() Signup and view all the answers

Study Notes

C Program: File I/O

Overview of File I/O

File I/O (Input/Output) in C allows the program to read from and write to files.
Essential for data persistence beyond program execution.

File Operations

Opening a File
- Use fopen() function:
  - Syntax: FILE *fopen(const char *filename, const char *mode);
  - Modes:
    - "r": Read (file must exist)
    - "w": Write (creates a new file or truncates existing)
    - "a": Append (adds to the end of the file)
    - "rb", "wb", "ab": Read/Write in binary mode
Closing a File
- Use fclose() function to release resources.
- Syntax: int fclose(FILE *stream);

Reading from Files

fscanf(): Reads formatted input from a file.
- Syntax: int fscanf(FILE *stream, const char *format, ...);
fgets(): Reads a line from a file.
- Syntax: char *fgets(char *str, int n, FILE *stream);
fgetc(): Reads a single character.
- Syntax: int fgetc(FILE *stream);

Writing to Files

fprintf(): Writes formatted output to a file.
- Syntax: int fprintf(FILE *stream, const char *format, ...);
fputs(): Writes a string to a file.
- Syntax: int fputs(const char *str, FILE *stream);
fputc(): Writes a single character to a file.
- Syntax: int fputc(int char, FILE *stream);

Error Handling

Check for successful file operations:
- After opening, check if the file pointer is NULL.
- After reading/writing, check the return values of functions.

Example Code Snippet

#include <stdio.h>

int main() {
    FILE *file;
    char buffer[100];

    // Open file for writing
    file = fopen("example.txt", "w");
    if (file == NULL) {
        perror("Error opening file");
        return -1;
    }

    // Write to file
    fprintf(file, "Hello, World!\n");
    fclose(file);

    // Open file for reading
    file = fopen("example.txt", "r");
    if (file == NULL) {
        perror("Error opening file");
        return -1;
    }

    // Read from file
    fgets(buffer, sizeof(buffer), file);
    printf("%s", buffer);
    fclose(file);

    return 0;
}

Tips

Always close files to avoid memory leaks.
Use feof() and ferror() to check for end-of-file and errors, respectively.
Remember to handle binary files separately if needed.