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How to make it so the pointer == null test passes?

allUsers + 3 means simply the forth struct customer_account over from the address allocated to allUsers. It cannot possibly be NULL under any circumstances. It is the same as


Its content can be zeroed out, but the pointer itself is a positive offset from a valid pointer, and the standard requires it to be non-NULL, because it is one byte past the end of the dynamically allocated array.

To see what is going on, do this experiment:

for (int i = 0 ; i != 4 ; i++) {
", (void*)(allUsers + i));

This will print four numbers - the first is allUsers, the second is allUsers plus the size of one struct customer_account, the third is allUsers plus the size of two struct customer_account, and the last one is what your program prints. As you can see, these addresses are a result of simple calculations, and have nothing to do with the content of the actual array.

Categories : C

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