C/stdio.h/ferror

//Declaration:  int ferror(FILE *stream); 
//Return:       0: no error has occurred.   
                Nonzero: an error has occurred.  
  #include <stdio.h>
  #include <stdlib.h>
  int main(void){
     FILE *fp;
     if((fp=fopen("test", "rb"))==NULL) {
        printf("Cannot open file.\n");
        exit(1);
     }
     putc("C", fp);
     if(ferror(fp)) {
       printf("File Error\n");
       exit(1);
     }
    
     fclose(fp);
     return 0;
  }