StackOverflow2013

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copied!<p>Unsigned intgers are an artifact from the past. This is from the time, where processors could do unsigned arithmetic a little bit faster. </p> <p>This is a case of <em>premature optimization</em> which is considered evil.</p> <p>Actually, in 2005 when AMD introduced x86_64 (or AMD64, how it was then called), the 64 bit architecture for x86, they brought the ghosts of the past back: If a signed integer is used as an index and the compiler can not prove that it is never negative, is has to insert a 32 to 64 bit sign extension instruction - because the default 32 to 64 bit extension is <em>unsigned</em> (the upper half of a 64 bit register gets cleard if you move a 32 bit value into it).</p> <p>But I would recommend against using <em>unsigned</em> in any arithmetic at all, being it pointer arithmetic or just simple numbers.</p> <p><code>for( unsigned int i = foo.Length() - 1; i >= 0; --i ) {}</code></p> <p>Any recent compiler will warn about such an construct, with <em>condition ist always true</em> or similar. With using a signed variable you avoid such pitfalls at all. Instead use <code>ptrdiff_t</code>.</p> <p>A problem might be the c++ library, it often uses an unsigned type for <code>size_t</code>, which is required because of some rare corner cases with very large sizes (between 2^31 and 2^32) on 32 bit systems with certain boot switches ( /3GB windows).</p> <p>There are many more, comparisons between signed and unsigned come to my mind, where the signed value automagically gets promoted to a unsigned and thus becomes a huge positive number, when it has been a small negative before.</p> <p>One exception for using <code>unsigned</code> exists: For bit fields, flags, masks it is quite common. Usually it doesn't make sense at all to interpret the value of these variables as a magnitude, and the reader may deduce from the type that this variable is to be interpreted in bits.</p> <blockquote> <p>The result will never be a negative value (as the section number, by the way). So why use a signed integer for this?</p> </blockquote> <p>Because you might want to compare the return value to a signed value, which is actually negative. The comparison should return <em>true</em> in that case, but the C standard specifies that the signed get promoted to an unsigned in that case and you will get a <em>false</em> instead. I don't know about ObjectiveC though.</p>

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