ferror

#include <stdio.h>
#include <stdlib.h>
 
int main(void)
{
    FILE* fp = fopen("test.txt", "r");
    if(!fp) {
        perror("File opening failed");
        return EXIT_FAILURE;
    }
 
    int c; // note: int, not char, required to handle EOF
    while ((c = fgetc(fp)) != EOF) { // standard C I/O file reading loop
       putchar(c);
    }
 
    if (ferror(fp))
        puts("I/O error when reading");
    else if (feof(fp))
        puts("End of file reached successfully");
 
    fclose(fp);
}