apart. In every case, programmers using this technique should use the safe versions in every instance where free() would be used; failing in doing so leads again to the problem. Also, this solution is limited to the scope of a single program or project, and should be properly documented. Among more structured solutions, a popular technique to avoid dangling pointers in C++ is to use smart pointers. A smart pointer typically uses reference counting to reclaim objects. Some other techniques include the tombstones method and the locks-and-keys method. Another approach is to use the Boehm garbage collector, a conservative garbage collector that replaces standard memory allocation functions in C and C++ with a garbage collector. This approach completely eliminates dangling pointer errors by disabling frees, and reclaiming objects by garbage collection. In languages like Java, dangling pointers cannot occur because there is no mechanism to explicitly deallocate memory. Rather, the garbage collector may deallocate memory, but only when the object is no longer reachable from any references. In the language Rust, the type system has been extended to include also the variables lifetimes and resource acquisition is initialization. Unless one disables the features of the language, dangling pointers will be caught at compile time and reported as programming errors. Dangling pointer detection To expose dangling pointer errors, one common programming technique is to set pointers to the null pointer or to an invalid address once the storage they point to has been released. When the null pointer is dereferenced (in most languages) the program will immediately terminate—there is no potential for data corruption or unpredictable behavior. This makes the underlying programming mistake easier to find and resolve. This technique does not help when there are multiple copies of the pointer. Some debuggers will automatically overwrite and destroy data that has been freed, usually with a specific pattern, such as 0xDEADBEEF (Microsoft's Visual C/C++ debugger, for example, uses 0xCC, 0xCD or 0xDD depending on what has been freed). This usually prevents the data from being reused by making it useless and also very prominent (the pattern serves to show the programmer that the memory has already been freed). Tools such as Polyspace, TotalView, Valgrind, Mudflap, AddressSanitizer, or tools based on LLVM can also be used to detect uses of dangling pointers. Other tools (SoftBound, Insure++, and CheckPointer) instrument the source code to collect and track legitimate values for pointers ("metadata") and