Why is the fgets function deprecated?

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No, fgets is not actually deprecated in C99 or the current standard, C11. But the author of that tutorial is right that fgets will not stop when it encounters a NUL, and has no mechanism for reporting its reading of such a character.

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.

(ยง7.21.7.2)

GNU’s getdelim and getline have been standardized in POSIX 2008, so if you’re targeting a POSIX platform, then it might not be a bad idea to use those instead.

EDIT I thought there was absolutely no safe way to use fgets in the face of NUL characters, but R.. (see comments) pointed out there is:

char buf[256];

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

Now look for the last non-\n character in buf. I wouldn’t actually recommend this kludge, though.

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