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where the integer expression size and the declaration of vla are both evaluated at runtime. If the size argument supplied to a variable length array is not a positive integer value, the behavior is undefined. (see See undefined behavior 75.). Additionally, if the magnitude of the argument is excessive, the program may behave in an unexpected way. An attacker may be able to leverage this behavior to overwrite critical program data [Griffiths 2006]. The programmer must ensure that size arguments to variable length arrays, especially those derived from untrusted data, are in a valid range.
Because variable length arrays are a conditionally supported feature of C11, their use in portable code should be guarded by testing the value of the macro __STDC_NO_VLA__. Implementations that do not support variable length arrays indicate so it by setting __STDC_NO_VLA__ to the integer constant 1.
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