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The information is in the instruction pointer. You jump to the place that deallocates the last resource that was allocated, followed by the second-to-last etc.

Also, free(NULL) is not well-defined in C, and other resource types aren't so easy to check. delete nullptr in C++ is well-defined, but you rarely need it.

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> free(NULL) is not well-defined in C

Oh yes it is: https://stackoverflow.com/questions/1938735/does-freeptr-whe...

I stand corrected. So, these days, null checks before free() are just for compatibility with very old systems, or more likely "tradition". I wonder where I got my wrong information? I have even seen null checks before delete in C++ code recently written by C programmers :o

When it is in the normal execution path, the test avoids a function call, so there's a little bit of performance gain.

It can also be a bit self-documenting, or be a place-holder if there is for example stuff to delete in a loop (elements of an array) before releasing the pointer itself (the array).

I don't know, when you read it, sometimes it feels natural and meaningful, and sometimes you know that the author didn't know that free() handles NULL all right.

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