c - 为什么不推荐使用 fgets 函数？

Question

来自 The GNU C Programming Tutorial :

The fgets ("file get string") function is similar to the gets function. This function is deprecated -- that means it is obsolete and it is strongly suggested you do not use it -- because it is dangerous. It is dangerous because if the input data contains a null character, you can't tell. Don't use fgets unless you know the data cannot contain a null. Don't use it to read files edited by the user because, if the user inserts a null character, you should either handle it properly or print a clear error message. Always use getline or getdelim instead of fgets if you can.

我认为 fgets 函数在遇到 \0 或 \n 时停止；为什么当 fgets 应该正确处理输入时，此手册页建议空字节是“危险的”？此外，getline 和 fgets 之间有什么区别，fgets 函数是否真正被认为已弃用 < strong>C99 还是 future 的 C 标准？

Answer 1

不，fgets 实际上并未在 C99 或当前标准 C11 中弃用。但是该教程的作者是对的，fgets 在遇到 NUL 时不会停止，并且没有报告读取此类字符的机制。

The fgets function reads at most one less than the number of characters specified by n from the stream pointed to by stream into the array pointed to by s. No additional characters are read after a new-line character (which is retained) or after end-of-file.

(§7.21.7.2)

GNU 的 getdelim 和 getline 已在 POSIX 2008 中标准化，因此如果您的目标是 POSIX 平台，那么改用这些平台可能不是一个坏主意。

编辑 我认为在 NUL 字符面前使用 fgets 绝对没有安全的方法，但是 R..(见评论)指出有:

char buf[256];

memset(buf, '\n', sizeof(buf));  // fgets will never write a newline
fgets(buf, sizeof(buf), fp);

现在在 buf 中查找最后一个非 \n 字符。不过，我实际上并不推荐这种组合。