64 bit large mallocs

Question

What are the reasons a malloc() would fail, especially in 64 bit?

My specific problem is trying to malloc a huge 10GB chunk of RAM on a 64 bit system. The machine ha

Answer 1

The problem is that Visual Studio does not define WIN64 when you compile a 64 bit application, it usually still keeps WIN32, which is wrong for 64 bit apps. This then causes the run-time to use the 32-bit value when _HEAP_MAXREQ is defined, so all large malloc() will fail. If you change your project (under project properties, preprocessed definitions) to be WIN64, then the very large malloc() should have no trouble at all.