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    <p>You won't strike buffer overflow problems if you enter more characters than can be safely stored since <code>fgets</code> restricts the input. It also adds a null terminator (assuming buffer size is greater than 0, of course).</p> <p>However, you <em>will</em> have problems with information being left in the input buffer the next time you try to read something - this is something that users will find very annoying, entering something like <code>hello again</code> and having it treated as two separate inputs like <code>hello ag</code> and <code>ain</code>. And there's no indication given by <code>fgets</code> that it stopped retrieving input before the end of the line so, as far as your code is aware, everything is fine.</p> <p>The major things you need to look out for (re buffer overflows on input) are, at a minimum, <code>scanf</code> with an unbounded <code>%s</code> format string and <code>gets</code>, which has no limiting size argument, neither of which are in your code.</p> <p>If you're looking for a more robust input solution with size limiting, prompting and buffer clearing, check out this code, which provides all those features:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;string.h&gt; #define OK 0 #define NO_INPUT 1 #define TOO_LONG 2 static int getLine (char *prmpt, char *buff, size_t sz) { int ch, extra; // Get line with buffer overrun protection. if (prmpt != NULL) { printf ("%s", prmpt); fflush (stdout); } if (fgets (buff, sz, stdin) == NULL) return NO_INPUT; // If it was too long, there'll be no newline. In that case, we flush // to end of line so that excess doesn't affect the next call. if (buff[strlen(buff)-1] != '\n') { extra = 0; while (((ch = getchar()) != '\n') &amp;&amp; (ch != EOF)) extra = 1; return (extra == 1) ? TOO_LONG : OK; } // Otherwise remove newline and give string back to caller. buff[strlen(buff)-1] = '\0'; return OK; } </code></pre> <p>&nbsp;</p> <pre><code>// Test program for getLine(). int main (void) { int rc; char buff[10]; rc = getLine ("Enter string&gt; ", buff, sizeof(buff)); if (rc == NO_INPUT) { // Extra NL since my system doesn't output that on EOF. printf ("\nNo input\n"); return 1; } if (rc == TOO_LONG) { printf ("Input too long [%s]\n", buff); rc = getLine ("Hit ENTER to check remains&gt; ", buff, sizeof(buff)); printf ("Excess [%s]\n", buff); return 1; } printf ("OK [%s]\n", buff); return 0; } </code></pre> <p>And, doing some basic tests:</p> <pre><code>pax&gt; ./prog Enter string&gt; [CTRL-D] No input pax&gt; ./prog Enter string&gt; x OK [x] pax&gt; ./prog Enter string&gt; hello OK [hello] pax&gt; ./prog Enter string&gt; hello from earth Input too long [hello fro] Hit ENTER to check remains&gt; [ENTER] Excess [] pax&gt; ./prog Enter string&gt; i am pax OK [i am pax] </code></pre>
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    1. POIs this vulnerable to a stack overflow?
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    1. POIs this vulnerable to a stack overflow?
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    1. COErr.. no. `fgets()` always nul-terminates the result, as long as the supplied `size` was at least 1.
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    2. COSorry, should have made that "size has to be big enough for the terminator otherwise it's not stored" clear in the first paragraph - fixed.
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