C is not your friend: sizeof and side-effects

Re:C is not your friend: sizeof and side-effects by gandalf013 on Wednesday April 19, 2017 @06:59PM (#14152540)

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

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Re:C is not your friend: sizeof and side-effects by kazinator on Wednesday April 19, 2017 @07:59PM (#14152880)

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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