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copied!<p>C and C++ can run on many different architectures, and machine types. Consequently, they can have different representations of numbers: Two's complement, and Ones' complement being the most common. In general you should not rely on a particular representation in your program.</p> <p>For unsigned integer types (<code>size_t</code> being one of those), the C standard (and the C++ standard too, I think) specifies precise overflow rules. In short, if <code>SIZE_MAX</code> is the maximum value of the type <code>size_t</code>, then the expression</p> <p><code>(size_t) (SIZE_MAX + 1)</code></p> <p>is guaranteed to be <code>0</code>, and therefore, you can be sure that <code>(size_t) -1</code> is equal to <code>SIZE_MAX</code>. The same holds true for other unsigned types.</p> <p>Note that the above holds true:</p> <ul> <li>for all unsigned types,</li> <li><em>even if the underlying machine doesn't represent numbers in Two's complement</em>. In this case, the compiler has to make sure the identity holds true.</li> </ul> <p>Also, the above means that you can't rely on specific representations for <em>signed</em> types.</p> <p><em>Edit</em>: In order to answer some of the comments:</p> <p>Let's say we have a code snippet like:</p> <pre><code>int i = -1; long j = i; </code></pre> <p>There is a type conversion in the assignment to <code>j</code>. Assuming that <code>int</code> and <code>long</code> have different sizes (most [all?] 64-bit systems), the bit-patterns at memory locations for <code>i</code> and <code>j</code> are going to be different, because they have different sizes. The compiler makes sure that the <em>values</em> of <code>i</code> and <code>j</code> are <code>-1</code>.</p> <p>Similarly, when we do:</p> <pre><code>size_t s = (size_t) -1 </code></pre> <p>There is a type conversion going on. The <code>-1</code> is of type <code>int</code>. It has a bit-pattern, but that is irrelevant for this example because when the conversion to <code>size_t</code> takes place due to the cast, the compiler will translate the <em>value</em> according to the rules for the type (<code>size_t</code> in this case). Thus, even if <code>int</code> and <code>size_t</code> have different sizes, the standard guarantees that the value stored in <code>s</code> above will be the maximum value that <code>size_t</code> can take.</p> <p>If we do:</p> <pre><code>long j = LONG_MAX; int i = j; </code></pre> <p>If <code>LONG_MAX</code> is greater than <code>INT_MAX</code>, then the value in <code>i</code> is implementation-defined (C89, section 3.2.1.2).</p>

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