Print to File in C

The simplest way to print to a file in C is by using standard file I/O functions provided in the stdio.h library, such as fprintf, fputs, and fwrite.

In this tutorial, we will explore multiple scenarios for printing text to a file using different functions and approaches, making it easy for beginners to understand.

Example 1: Using fprintf to Write Formatted Text to a File

In this example, we will open a file in write mode and use fprintf to print formatted text into the file.

main.c

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#include <stdio.h>

int main() {
    FILE *fp = fopen("output.txt", "w"); // Open file in write mode
    if (fp == NULL) {
        perror("Error opening file");
        return 1;
    }
    
    // Write formatted text to the file using fprintf
    fprintf(fp, "Hello, World! This is a test: %d, %f\n", 100, 3.14);
    
    fclose(fp); // Close the file
    return 0;
}

Explanation:

  1. The variable fp is a pointer to a FILE object, obtained by calling fopen with the file name "output.txt" and mode "w" (write mode).
  2. fprintf is used to write formatted text to the file. Here, it prints a string with an integer (100) and a float (3.14).
  3. fclose is called to close the file once writing is complete, ensuring that all buffers are flushed and resources are freed.

Output:

Hello, World! This is a test: 100, 3.140000

Example 2: Using fputs to Write a String to a File

In this example, we will open a file in write mode and use fputs to write a simple string to the file.

main.c

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#include <stdio.h>

int main() {
    FILE *fp = fopen("output.txt", "w"); // Open file in write mode
    if (fp == NULL) {
        perror("Error opening file");
        return 1;
    }
    
    // Write a string to the file using fputs
    fputs("This is a simple string written using fputs.\n", fp);
    
    fclose(fp); // Close the file
    return 0;
}

Explanation:

  1. The file is opened in write mode using fopen, and a pointer fp is assigned.
  2. fputs is used to write a string directly to the file. Unlike fprintf, it does not support formatting.
  3. The file is then closed using fclose to ensure all data is properly saved.

Output:

This is a simple string written using fputs.

Example 3: Appending Text to a File

In this example, we will open a file in append mode so that we can add new content to the end of an existing file without overwriting the existing data.

main.c

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#include <stdio.h>

int main() {
    FILE *fp = fopen("output.txt", "a"); // Open file in append mode
    if (fp == NULL) {
        perror("Error opening file");
        return 1;
    }
    
    // Append text to the file using fprintf
    fprintf(fp, "Appending new content to the file.\n");
    
    fclose(fp); // Close the file
    return 0;
}

Explanation:

  1. The file is opened in append mode ("a") using fopen. This mode allows data to be added to the end of the file.
  2. fprintf is then used to write a line of text that will be added to any existing content in the file.
  3. Finally, the file is closed using fclose to complete the operation.

Output:

Appending new content to the file.

Conclusion

In this tutorial, we learned multiple ways to print text to a file in C using various functions such as fprintf and fputs. We also explored how to open a file in different modes (write and append) to suit different needs.