gdb.info: Debugging C

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GDB and C

The `set print union' and `show print union' commands apply to the
`union' type.  When set to `on', any `union' that is inside a `struct'
or `class' is also printed.  Otherwise, it appears as `{...}'.
   The `@' operator aids in the debugging of dynamic arrays, formed
with pointers and a memory allocation function.  *Note Expressions:
Expressions.