10.2 Variables in Data Memory
Most variables are ultimately positioned into the data memory. The
exceptions are non-auto variables which are qualified as
const, which are placed in the program memory space, see 9.9.1 Const Type Qualifier.
Due to the fundamentally different way in which auto variables and
non-auto variables are allocated memory, they are discussed
separately. To use the C/C++ language terminology, these two groups of variables are
those with automatic storage duration and those with permanent storage duration,
respectively.
Note: The terms “local” and “global” are commonly used to describe variables, but are not
ones defined by the language standard. The term “local variable” is often taken to mean
a variable which has scope inside a function, and “global variable” is one which has
scope throughout the entire program. However, the C/C++ language has three common
scopes: block, file (that is, internal linkage) and program (that is, external linkage),
so using only two terms to describe these can be confusing. For example, a
static variable defined outside a function has scope only in that
file, so it is not globally accessible, but it can be accessed by more than one function
inside that file, so it is not local to any one function either. In terms of memory
allocation, variables are allocated space based on whether it is an
auto or not, hence the grouping in the following sections.