Error Handling in File I/O

Error handling is a critical part of robust file I/O programming. Operations involving external resources like the file system are prone to failure for many reasons: a file might not exist, you might not have permission to read or write, the disk could be full, or a hardware error could occur. Your program should be ableto anticipate and handle these situations gracefully instead of crashing. The first line of defense is checking the return value of `fopen()`. If it returns `NULL`, the file could not be opened, and your program should not proceed with any further operations on that file pointer. You should inform the user of the error and exit or take corrective action. For other I/O functions, their return values can also indicate errors. For example, `fread()` and `fwrite()` return the number of items successfully processed, which might be less than what you requested if an error occurred. `fscanf()` returns the number of items assigned, or `EOF` if the end-of-file is reached before any assignment is made. The C standard library provides two functions to get more specific information about errors: `ferror()` and `feof()`. The `feof(fp)` function returns a non-zero value if the end-of-file indicator for the stream `fp` is set, meaning you have tried to read past the end of the file. The `ferror(fp)` function returns a non-zero value if the error indicator for the stream is set, meaning an I/O error has occurred. You can use these functions, especially after a read or write operation returns an unexpected value, to determine the cause of the failure.