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Rita Kairu
Rita Kairu

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A Quick Guide to File Manipulation (I/O) in C

#c #programming #tutorial

File operations in C are essential for reading from and writing to files on the system. They involve several functions and concepts that enable you to manipulate files efficiently. Here's a brief overview of file operations in C:

1. File Pointers

  • File pointers are used to handle files in C programs.
  • They are of type FILE and are declared using the FILE structure.
  • Example: FILE *fp;

2. Opening Files

  • fopen() function is used to open files.
  • Syntax: FILE *fopen(const char *filename, const char *mode);
  • Modes:
    • "r": Read mode
    • "w": Write mode (creates a new file or overwrites existing content)
    • "a": Append mode (appends data at the end of the file)
    • "r+": Read/write mode (file must exist)
    • "w+": Read/write mode (creates a new file or overwrites existing content)
    • "a+": Read/append mode (file is created if it does not exist)
  • Returns a pointer to the file.

3. Closing Files

  • fclose() function is used to close files.
  • Syntax: int fclose(FILE *fp);
  • It flushes any buffered data and releases the associated file descriptor.

4. Reading from Files

  • fgetc() reads a character from the file.
  • fgets() reads a line from the file.
  • fread() reads blocks of data from the file.
  • Example: 
  char buffer[255];
  fgets(buffer, 255, fp); // Reads a line from the file into buffer
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5. Writing to Files

  • fputc() writes a character to the file.
  • fputs() writes a string to the file.
  • fwrite() writes blocks of data to the file.
  • Example: 
  fprintf(fp, "This is a formatted string: %s\n", str);
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6. Error Handling

  • Always check if file operations succeed.
  • Use feof() and ferror() to handle end-of-file and error conditions respectively.

7. File Positioning

  • fseek() and rewind() are used to move the file pointer.
  • ftell() returns the current position of the file pointer.

8. Binary vs. Text Mode

  • Files can be opened in binary mode by adding 'b' to the mode string.
  • Binary mode prevents newline translation and treats file contents as binary data.

9. Error Handling

  • Always check the return values of file operations.
  • Handle errors gracefully to avoid unexpected behavior.

Sample Code: 

#include <stdio.h>

int main() {
    FILE *fp;
    char buffer[255];

    // Open file for writing
    fp = fopen("example.txt", "w+");
    if (fp == NULL) {
        printf("Error opening file!\n");
        return -1;
    }

    // Write to file
    fprintf(fp, "This is just an example!\n");

    // Read from file
    rewind(fp);
    fgets(buffer, 255, fp);
    printf("Content: %s", buffer);

    // Close file
    fclose(fp);

    return 0;
}
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Important Points:

  • Always close files after using them to prevent resource leaks.
  • Handle file operations errors appropriately.
  • Use binary mode when dealing with binary data.

Understanding file operations is crucial for many applications, especially those involving data storage and manipulation. Mastering file operations in C allows you to work with files seamlessly.

Top comments (2)

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pauljlucas profile image
Paul J. Lucas •

Without an example for each function, this really isn't comprehensive.

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thecodingcivilengineer profile image
Rita Kairu •

Thank you Paul for your honest feedback🌟.