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    <p>Since your <code>return_val</code> is an <code>unsigned int</code>, you should probably be using <code>strtoul()</code> which has been standard since C89 and is therefore supported by MSVC (whereas <code>strtoll()</code> has only been standard since C99 and is not supported by MSVC).</p> <p>Your testing of the error conditions is not adequate. You need to set <code>errno</code> to zero before calling the conversion function; you also need to detect whether an error was reported, which is trickier than it seems.</p> <p>Section §7.20.1.4 'The strtol, strtoll, strtoul, and strtoull functions' of the C99 standard says:</p> <blockquote> <p><strong>Returns</strong></p> <p>The <code>strtol</code>, <code>strtoll</code>, <code>strtoul</code>, and <code>strtoull</code> functions return the converted value, if any. If no conversion could be performed, zero is returned. If the correct value is outside the range of representable values, LONG_MIN, LONG_MAX, LLONG_MIN, LLONG_MAX, ULONG_MAX, or ULLONG_MAX is returned (according to the return type and sign of the value, if any), and the value of the macro ERANGE is stored in <code>errno</code>.</p> </blockquote> <p>You also have to read the look at the value stored in the <code>endptr</code> parameter to the conversion functions to tell that no conversion was performed (as opposed to a valid zero was converted).</p> <blockquote> <p>If the subject sequence is empty or does not have the expected form, no conversion is performed; the value of <code>nptr</code> is stored in the object pointed to by <code>endptr</code>, provided that <code>endptr</code> is not a null pointer.</p> </blockquote> <p>So, you must write code more like this (omitting the test against EINVAL because the standard does not mention these functions setting <code>errno</code> to EINVAL):</p> <pre><code>unsigned int return_val=0; if (index + 1 &lt;= argc - 1) { char *end; unsigned long ul; errno = 0; ul = strtoul(argv[index+1], &amp;end, 10); if ((ul == 0 &amp;&amp; end == argv[index+1]) || (ul == ULONG_MAX &amp;&amp; errno == ERANGE) || (ul &gt; UINT_MAX)) { fprintf(stderr, "Could not parse argument %s for switch %s!\n", argv[index], argv[index+1]); return 0; } retval = (unsigned int)ul; } </code></pre> <p>Note that this is simpler than the test for a signed integer conversion which must take into account the negative <code>&lt;type&gt;_MIN</code> limit as well as the <code>&lt;type&gt;_MAX</code> limit.</p> <p>Also note that you really should record the result in an <code>unsigned long</code> and then check whether it fits within your designated range, which may be limited to UINT_MAX (which can be less than ULONG_MAX in a Unix-like 64-bit environment).</p>
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    1. POWhat is wrong with the following C code?
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    1. USJonathan Leffler
    1. USJonathan Leffler
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    1. POWhat is wrong with the following C code?
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    1. CO`errno = ERANGE`?? :)
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    2. COalso, you should check for `retval > UINT_MAX` as well (before downcasting to `unsigned int`), in case it's on a 64-bit long platform.
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    3. CO@bdonlan: yes - thanks (to both comments). I fixed the downcast with the last paragraph without seeing your comment (but the first edition of the answer didn't include that, and your comment is spot on). I had missed my '=' instead of '==' typo (but the compiler would have warned me about it had I compiled the code).
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