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Local, automatic variables can assume unexpected values if they are used before they are initialized. C99 specifies, "If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate" \[[ISO/IEC 9899:1999|AA. C References#ISO/IEC 9899-1999]\]. In the common case, on architectures that make use of a program stack, this value defaults to whichever values are currently stored in stack memory. While uninitialized memory often contains zeroes, this is not guaranteed. Consequently, uninitialized memory can cause a program to behave in an unpredictable or unplanned manner and may provide an avenue for attack. |
In most cases, compilers warn about uninitialized variables. These warnings should be resolved as recommended by MSC00-A. Compile cleanly at high warning levels.
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