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45 lines
1.1 KiB
45 lines
1.1 KiB
/*
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* Illustrate a common 64-bit portability bug when 32-bit unsigned array
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* indices are used with 64-bit pointers.
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*/
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#include <stdio.h>
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#include <inttypes.h>
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int main(int argc, char *argv[]) {
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const char *test = "test string";
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const char *p;
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uint32_t uidx = 2;
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int32_t sidx = 2;
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printf("uidx == %ld (uint32_t), idx == %ld (int32t)\n",
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(long) uidx, (long) sidx);
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p = test;
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printf("test -> %p\n", (void *) p);
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p = &test[uidx + 1];
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printf("&test[uidx + 1] -> %p\n", (void *) p);
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p = &test[sidx + 1];
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printf("&test[sidx + 1] -> %p\n", (void *) p);
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/* This causes a problem: uidx - 3 is computed as an unsigned
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* value and results in 0xffffffffUL. Adding this value to a
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* 32-bit pointer is the same as subtracting 1 from the pointer.
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* But for 64-bit pointers these two are not the same.
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*/
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p = &test[uidx - 3];
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printf("&test[uidx - 3] -> %p\n", (void *) p);
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p = &test[sidx - 3];
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printf("&test[sidx - 3] -> %p\n", (void *) p);
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p = test + uidx - 3;
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printf("test + uidx - 3 -> %p\n", (void *) p);
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p = test + sidx - 3;
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printf("test + sidx - 3 -> %p\n", (void *) p);
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return 0;
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}
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