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    <p>What happens looks like this.</p> <pre><code>printf("%d", m); </code></pre> <p>On most systems the address of the string will get pushed on the stack, and then <code>'m'</code> as an integer (assuming it's an int/short/char). There is no warning because <code>printf</code> is basically declared as <code>'int printf(const char *, ...);'</code> - the ... meaning 'anything goes'.</p> <p>So since 'anything goes' some odd things happen when you put variables there. Any integral type smaller than an int goes as an int - things like that. Sending nothing at all is ok as well.</p> <p>In the printf implementation (or at least a 'simple' implementation) you will find usage of <code>va_list</code> and <code>va_arg</code> (names sometime differ slightly based on conformance). These are what an implementation uses to walk around the '...' part of the argument list. Problem here is that there is NO type checking. Since there is no type checking, <code>printf</code> will pull random data off the execution stack when it looks at the format string <code>("%d")</code> and thinks there is supposed to be an <code>'int'</code> next.</p> <p>Random shot in the dark would say that the function call you made just before printf possibly passed <code>'m-1'</code> as it's second parm? That's one of many possibilities - but it would be interesting if this happened to be the case. :)</p> <p>Good luck.</p> <p>By the way - most modern compilers (GCC I believe?) have warnings that can be enabled to detect this problem. Lint does as well I believe. Unfortunately I think with VC you need to use the /analyze flag instead of getting for free.</p>
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    1. POBehaviour of printf when printing a %d without supplying variable name
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    1. COI see. Normally I wouldn't be bothered and just treat it as garbage value, but since it just so happened to output sensible data I thought maybe there is something more. You've made it very clear, thank you for your help Joe.
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    2. COgcc's flag to show this problem is -Wformat
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    3. COThe parameters usually get pushed on the stack from right to left. Then when the string is popped, it pops from the stack as it needs parameters.
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