TotalView Users Guide - CI Wiki

Why is There an Expression System?
Figure 239: Displaying the
Value of the Last
Statement
code within TotalView. TotalView is not using the compiler you used to create
your program or any other compiler or interpreter on your system.
Notice the last statement in Figure 239. TotalView displays the value
returned by the last statement. This value is displayed. (See “Displaying the
Value of the Last Statement” on page 384.)
TotalView assumes that there is always a return value, even if it’s evaluating
a loop or the results of a subroutine returning a void. The results are, of
course, not well-defined. If the value returned is not well-defined, TotalView
displays a zero in the Result area.
The code within eval points and the Evaluate Window does not run in the
same address space as that in which your program runs. Because TotalView
is a debugger, it knows how to reach into your program’s address space.
The reverse isn’t true: your program can’t reach into the TotalView address
space. This forces some limitations upon what you can do. In particular,
you can not enter anything that directly or indirectly needs to pass an
address of variable defined within the TotalView expression into your program.
Similarly, invoking a function that expects a pointer to a value and
whose value is created within TotalView can’t work. However, you can
invoke a function whose parameter is an address and you name something
within that program’s address space. For example, you could say something
like adder(an_array) if an_array is contained within your program.
Using C++
The TotalView expression system is able to interpret the way you define
your classes and their inheritance hierarchy. For example, if you declare a
method in a base class and you invoke upon an object instantiated from a
derived class, TotalView knows how to access the function. It also under-
384 Chapter 17: Evaluating Expressions