在循环中 fread 后检查 EOF

Question

我明白了为什么下面的循环给我 bad input，重新 Why is “while ( !feof (file) )” always wrong?

do {
    if (fread(buf, 1, siz, stdin) != siz) {
        if (feof(stdin))
            fputs("bad input\n", stderr);
        else /* implying ferror(stdin) */
            perror("fread() failed");
        return EXIT_FAILURE;
    }
    use(buf);
} while (!feof(stdin));

是否不可避免地要编写一些辅助 function/weird 调用以正确（？）按照 ungetc(getchar(), stdin) 检查 EOF 还是有更好的方法？

Answer 1

我会做类似的事情

size_t nread;
while ((nread = fread(buf, 1, siz, stdin)) == siz) {
    use(buf);
}

if (feof(stdin)) {
    if (nread == 0) {
        /* Normal EOF; do nothing. I would not actually
           write this branch. :-) */
    } else {
        /* Short read. */
        fputs("bad data\n", stderr); }
    }
} else {
    perror("fread");
}

Answer 2

无需使用 ungetc 检查文件结尾。相反，您可以将循环重写为以下内容：

while ( fread(buf, 1, siz, stdin) == siz )
{
    use(buf);
}

//verify that the loop was terminated due to end-of-file and not due
//to stream error
if ( ferror(stdin) )
{
    perror( "fread() failed" );
    return EXIT_FAILURE;
}

//No stream error occurred, so the loop must have been terminated due
//to end-of-file. Therefore, everything is ok and we can continue
//running the program normally.

根据情况，您可能还想额外检查是否发生了部分读取，并将其视为错误。请参阅其他答案，了解如何做到这一点。

在循环中 fread 后检查 EOF

Check EOF after fread in a loop

c

stdin

fread

eof

feof