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    <p>You can prevent them from crashing by not using them. :)</p> <p>In all seriousness, there is almost no safe way to use variable-length arrays to make your life easier unless you have strong bounds on the size. On the other hand, you can use them conditionally, in ways like this:</p> <pre><code>char vla_buf[n &lt; 1000 ? n : 1]; char *buf = sizeof vla_buf &lt; n ? malloc(n) : vla_buf; if (!buf) goto error; /* ... Do stuff with buf ... */ if (buf != vla_buf) free(buf); </code></pre> <p>While this looks like useless pain, it can make a huge performance difference, especially in threaded applications where many calls to <code>malloc</code> and <code>free</code> could result in lock contention. (A notable side benefit of this trick is that you can support old compilers without VLAs by simply replacing <code>[n &lt; 1000 ? n : 1]</code> with <code>1000</code>, e.g. with a macro.)</p> <p>Another obscure case where VLAs may be useful is in recursive algorithms where you know the total number of array entries required across all levels of recursion is bounded by <code>n</code>, where <code>n</code> is small enough you're confident it won't overflow the stack, but where there could be up to <code>n</code> levels of recursion and individual levels that use up to <code>n</code> elements. Prior to C99, the only way to handle this case without taking <code>n^2</code> stack space was to use <code>malloc</code>. With VLAs, you can solve the problem entirely on the stack.</p> <p>Keep in mind, these cases where VLAs are really beneficial are pretty damn rare. Normally VLA is just a way to deceive yourself that memory management is easy, until you get bit by the resulting (trivial-to-exploit) vulnerabilities you've created. :-)</p> <p><strong>Edit:</strong> To better address OP's original question:</p> <pre><code>#define MAX_VLA 10000 int bar(size_t n) { int arr[n &lt;= MAX_VLA ? n : 1]; if (sizeof arr/sizeof *arr &lt; n) return ENOMEM; /* ... */ return 0; } </code></pre>
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    1. POHow do you prevent variable-length arrays from crashing when there is not enough memory?
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    1. COIn your first example, you might as well just use `[1000]` everywhere, since you've already determined that that value won't (shouldn't) crash. The recursive algorithm appears to be the real use case.
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    2. COYou gave me some good ideas, but I think the easiest is to simply start the function with `if (n <= MAX_VLA) { int arr[n]; ... }`. Thanks.
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    3. CONote that there are bugs in your examples. :-) It should be `if ((sizeof arr)/(sizeof int) < n)`, etc.
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