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POC/C++ post-increment/-decrement and function call
 

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  1. POC/C++ post-increment/-decrement and function call
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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/4176328/undefined-behavior-and-sequence-points">Undefined Behavior and Sequence Points</a> </p> </blockquote> <p>I am using microsoft visual c++. Look at the following example:</p> <pre><code>int n = 5; char *str = new char[32]; strcpy(str, "hello world"); memcpy(&amp;str[n], &amp;str[n+1], 6+n--); printf(str); // output is "hell world" </code></pre> <p>So unexpectadly my compiler produces code that <strong>first</strong> decrements n and then executes memcpy. The following source will do what i expected to happen:</p> <pre><code>int n = 5; char *str = new char[32]; strcpy(str, "hello world"); memcpy(&amp;str[n], &amp;str[n+1], 6+n); n--; printf(str); // output is "helloworld" </code></pre> <p>First I tried to explain it to myself. The last parameter gets pushed on the stack first, so it may be evaluated first. But I really believe that post increment/decrement guarantee to be evaluated after the next semicolon.</p> <p>So I ran the following test:</p> <pre><code>void foo(int first, int second) { printf("first: %i / second: %i", first, second); } int n = 10; foo(n, n--); </code></pre> <p>This will output "first: 10 / second: 10".</p> <p>So my question is: Is there any defined behaviour to this situation? Can somebody point me to a document where this is described? Have I found a compiler bug ~~O.O~~?</p> <p>The example is simplyfied to not make sence anymore, it just demonstrates my problem and works by itself.</p>
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    1. UStyp1232
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    1. COIs there any defined behaviour => no
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    2. CO@ipc: This is puzzling me every time: why is the behavior "undefined" rather than just "unspecified"? Isn't just the order of evaluation of the arguments which is unspecified?
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    3. COhttp://stackoverflow.com/questions/376278/parameter-evaluation-order-before-a-function-calling-in-c
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