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    <p><code>2500000000</code> doesn't fit in an <code>int</code>, so the compiler correctly interprets it as a <code>long</code> (or <code>long long</code>, or a type where it fits). <code>1250000000</code> does, and so does <code>2</code>. The parameter to <code>sizeof</code> <strong>isn't evaluated</strong>, so the compiler can't possibly know that the multiplication doesn't fit in an <code>int</code>, and so returns the size of an <code>int</code>.</p> <p>Also, even if the parameter was evaluated, you'd likely get an overflow (and undefined behavior), but probably still resulting in <code>4</code>.</p> <p>Here:</p> <pre><code>#include &lt;iostream&gt; int main() { long long x = 1250000000 * 2; std::cout &lt;&lt; x; } </code></pre> <p>can you guess the output? If you think it's <code>2500000000</code>, you'd be wrong. The type of the expression <code>1250000000 * 2</code> is <code>int</code>, because the operands are <code>int</code> and <code>int</code> and multiplication isn't automagically promoted to a larger data type if it doesn't fit.</p> <p><a href="http://ideone.com/4Adf97">http://ideone.com/4Adf97</a></p> <p>So here, gcc says it's <code>-1794967296</code>, but it's undefined behavior, so that could be any number. This number does fit into an <code>int</code>.</p> <p>In addition, if you cast one of the operands to the expected type (much like you cast integers when dividing if you're looking for a non-integer result), you'll see this working:</p> <pre><code>#include &lt;iostream&gt; int main() { long long x = (long long)1250000000 * 2; std::cout &lt;&lt; x; } </code></pre> <p>yields the correct <code>2500000000</code>.</p>
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    1. POIn C, sizeof operator returns 8 bytes when passing 2.5m but 4 bytes when passing 1.25m * 2
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    1. USLuchian Grigore
    1. USLuchian Grigore
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    1. POIn C, sizeof operator returns 8 bytes when passing 2.5m but 4 bytes when passing 1.25m * 2
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    1. COYes, for VC++, MSDN says that an expression is not evaluated - http://msdn.microsoft.com/en-us/library/4s7x1k91(v=vs.71).aspx
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      1. USRoger Rowland
    2. CO@RogerRowland most importantly, the standard says the operand of `sizeof` is not evaluated.
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      1. USLuchian Grigore
    3. CO@LuchianGrigore i didn't get how sizeof of expression2 is 4? [new user]
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      1. USDineshkumar
 

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