Debugging with GDB Manual (5900-1473; WDB 6.2; January 2011)

@ '@' is a binary operator for treating parts of memory as arrays. Refer
to See “Artificial arrays” (page 78), for more information.
:: '::' allows you to specify a variable in terms of the file or function
where it is defined. See “Program variables” (page 77).
{type} addr Refers to an object of type type stored at address addr in memory.
addr may be any expression whose value is an integer or pointer
(but parentheses are required around binary operators, just as in a
cast). This construct is allowed regardless of what kind of data is
normally supposed to reside at addr.
8.2 Program variables
The most common kind of expression to use is the name of a variable in your program.
Variables in expressions are understood in the selected stack frame (see “Selecting a
frame” (page 68); they must be either:
• global (or file-static)
or
• visible according to the scope rules of the programming language from the point of
execution in that frame
This means that in the function
foo (a)
int a;
{
bar (a);
{
int b = test ();
bar (b);
}
}
you can examine and use the variable a whenever your program is executing within the
function foo, but you can only use or examine the variable b while your program is
executing inside the block where b is declared.
However, you can refer to a variable or function whose scope is a single source file even
if the current execution point is not in this file. But it is possible to have more than one
such variable or function with the same name (in different source files). If that happens,
referring to that name has unpredictable effects. If you wish, you can specify a static
variable in a particular function or file, using the colon-colon notation:
file::variable
function::variable
Here file or function is the name of the context for the static variable. In the case
of file names, you can use quotes to make sure GDB parses the file name as a single
word. For example, to print a global value of x defined in 'f2.c':
8.2 Program variables 77