Static Functions in

About Static Functions

Functions have external linkage by default and can be called from any other file in the project. For more on linkage please see the linkage concept. A static function can only be called within the source file where it is defined.

For example

// file scope, internal linkage
// can only be called from within this file
static void some_function()
{
    // code snipped
}

// file scope, external linkage by default
// can be called from any other file in the project
int main()
{
    // code snipped
}

Even if a function is declared in a header, if it is defined as static it will not be callable from outside of its source file. A source file could include the header, call the static function declared in the header, and compile, but the linker will fail to find the static function definition. A function marked as static in a source file should not be declared in its header file.