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Comment by breadbox | Hacker News Reader

This flaw was pointed out while C99 was under review. The idea of changing sizeof to not be evaluated at compile-time did not sit well with a lot of people. Unfortunately, the alternative (sizeof not being usable with dynamic arrays) was clearly worse.

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Do you happen to know why that was perceived as worse? If I understand correctly the difference would be that you'd have to write (i * sizeof(char)) vs. (sizeof(char[i]))? Personally I'd even prefer the former.

A very common idiom is "T p = malloc(n sizeof *p)". That only works if sizeof doesn't evaluate its arguments.

Why not? Suppose you have a C99 VLA object, and you want to malloc the equivalent amount of space. Couldn't you just do this:

   int vla[nparam];
   int *pcopyspace = malloc(sizeof vla);

Here sizeof vla is basically just nparam sizeof(int).

vla* is evaluated to the extent of calculating its run-time size.

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