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Compiler-specific Features
Restrictions
There are restrictions when you qualify function and variable declarations, and function
definitions, with __weak.
Functions and variable declarations
A function or variable cannot be used both weakly and non weakly in the
same compilation. For example the following code uses f() weakly from
g() and h():
void f(void);
void g()
{
f();
}
__weak void f(void);
void h()
{
f();
}
It is not possible to use a function or variable weakly from the same
compilation that defines the function or variable. The following code uses
f() non weakly from h():
__weak void f(void);
void h()
{
f();
}
void f() {}
The linker does not load the function or variable from a library unless
another compilation uses the function or variable non weakly. If the
reference remains unresolved, its value is assumed to be NULL. Unresolved
references, however, are not NULL if the reference is from code to a
position-independent section or to a missing __weak function.
Function definitions
Weakly defined functions cannot be inlined.
Example
__weak const int c;
// assume 'c' is not present in final link
const int *f1() { return &c; } // '&c' returns non-NULL if
// compiled and linked /ropi
__weak int i;
// assume 'i' is not present in final link
int *f2() { return &i; } // '&i' returns non-NULL if
// compiled and linked /rwpi
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