Using fprintf to Write Formatted Output to a File in C programming

Using fprintf to Write Formatted Output to a File in C

The fprintf function in C is used to write formatted output to a file. It works similarly to printf, but instead of printing to the standard output (console), it writes the formatted string to a file stream.

Syntax

The syntax for fprintf is as follows:

int fprintf(FILE *stream, const char *format, ...);

Where:

• stream is a pointer to a FILE object that identifies the output stream (e.g., a file).
• format is the format string that specifies how subsequent arguments are formatted.
• ... represents the additional arguments that are formatted according to the format string.

Example Code

#include <stdio.h>

int main() {
    FILE *file = fopen("output.txt", "w");
    int age = 25;
    float height = 1.80;

    if (file != NULL) {
        // Write formatted data to the file
        fprintf(file, "Age: %d years\nHeight: %.2f meters\n", age, height);
        
        fclose(file); // Close the file after writing
        printf("Data written to output.txt\n");
    } else {
        printf("Error opening file.\n");
    }

    return 0;
}

In this example:

• FILE *file = fopen("output.txt", "w"); opens a file named output.txt for writing. If the file does not exist, it will be created.
• fprintf(file, "Age: %d years\nHeight: %.2f meters\n", age, height); writes the formatted string to the file, including the values of age and height.
• fclose(file); closes the file after writing to ensure all data is saved and resources are freed.
• printf("Data written to output.txt\n"); confirms that the data has been successfully written to the file.

Key Points

• File Handling: Always check if the file is successfully opened before using fprintf. Handle potential errors if the file cannot be opened.
• Format Specifiers: Use format specifiers in fprintf to format data as needed (e.g., %d for integers, %f for floating-point numbers).
• Buffer Management: Ensure the data being written matches the format specifiers used in fprintf.

Note: The fprintf function is useful for creating formatted text files and logs. Make sure to handle file errors and always close the file after writing.