The **`clearerr` function** is part of the `<stdio.h>` header file in C. It takes in a single parameter: a `filestream`. 

It is used to clear the end-of-file and error indicators for the given stream.

> Error indicator is stored in the `errno` variable defined in `<errno.h>` header file.

The illustration below shows how `clearerr` works:

# Declaration

The `clearerr` function is defined as follows:

```C
void clearerr(FILE *stream);
```
It takes a `filestream` as a parameter.

# Return type
The function does not return anything. Hence, the return type is `void`.

# Example

The following code snippet shows how we can use the `clearerr` function:

> We create a file named `file.txt`. Since we try to read a character from an empty file in `Line 9`, an error occurs, and the `errno` flag is set. We use the `clearerr` function to clear the error in `Line 13` and continue normal operation.

> Once the error is cleared, we can write to file in `Line 15` and attempt to reread a character in `Line 19`. No errors occur this time.

#include <stdio.h> // inlcude relevant libraries

int main () {
  
  FILE *filePointer;
  char c;
  
  filePointer = fopen("file.txt", "w"); // creating a new file 
  c = fgetc(filePointer); // file is empty to an error will occur
  if( ferror(filePointer)) {
    printf("Error in reading from file : file.txt\n");
  }
  clearerr(filePointer); // clear error status

  fprintf(filePointer, "Writing to file"); // writing to file
  fclose(filePointer);

  filePointer = fopen("file.txt", "r"); // open file with read mode
  c = fgetc(filePointer); // no error should occur now
  // normal operation continues
  printf("Character is %c", c); 
  fclose(filePointer);
   return(0);
}

What is clearerr in C?

Clears end-of-file and error indicators for filestreams, allowing operations to resume normally after errors.