fwrite demo

Sure, here is a simple demonstration of using the `fwrite` function in C:

#include <stdio.h>

int main() {
    FILE *fp;
    char data[] = "Hello, CSDN!";

    // Open file for writing
    fp = fopen("output.txt", "w");
    if (fp == NULL) {
        printf("Failed to open file.\n");
        return 1;
    }

    // Write data to file
    fwrite(data, sizeof(char), sizeof(data) - 1, fp);

    // Close file
    fclose(fp);

    printf("Data written to file.\n");

    return 0;
}

In this example, we include the `stdio.h` library for file I/O operations. We declare a file pointer `fp` and a character array `data` containing the string we want to write to the file.

We open a file named "output.txt" in write mode using `fopen`. If the file fails to open, an error message is printed and the program returns. Otherwise, we use `fwrite` to write the contents of the `data` array to the file.

After writing the data, we close the file using `fclose`. Finally, a success message is printed.