feof - cppreference.com

Verifica se o fim do fluxo determinado arquivo foi atingido.

valor diferente de zero se o fim do fluxo foi atingido, de outro modo 0

Original:

This function only reports the stream state as reported by the most recent I/O operation, it does not examine the associated data source. For example, if the most recent I/O was a fgetc, which returned the last byte of a file, feof returns non-zero. The next fgetc fails and changes the stream state to end-of-file. Only then feof returns zero.

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Em utilização normal, o processamento pára no fluxo de entrada de qualquer erro, e feof ferrror são então utilizados para distinguir entre as condições de erro diferentes.

#include <stdio.h>
#include <stdlib.h>

int main()
{
    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) { // typical file reading loop
       putchar(c);
    }

    if (ferror(fp))
        puts("I/O error when reading");
    else if (feof(fp))
        puts("End of file reached successfully");
}