Why does this if condition fail for comparison of negative and positive integers [duplicate]

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The problem is in your comparison:

    if ((-1) < SIZE)

sizeof typically returns an unsigned long, so SIZE will be unsigned long, whereas -1 is just an int. The rules for promotion in C and related languages mean that -1 will be converted to size_t before the comparison, so -1 will become a very large positive value (the maximum value of an unsigned long).

One way to fix this is to change the comparison to:

    if (-1 < (long long)SIZE)

although it’s actually a pointless comparison, since an unsigned value will always be >= 0 by definition, and the compiler may well warn you about this.

As subsequently noted by @Nobilis, you should always enable compiler warnings and take notice of them: if you had compiled with e.g. gcc -Wall ... the compiler would have warned you of your bug.

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