Sun Studio 12: C++ User's Guide

4.1 Linker Scoping

Use the following declaration specifiers to help constrain declarations and definitions of extern symbols. The scoping restraints you specify for a static archive or an object file will not take effect until the file is linked into a shared library or an executable. Despite this, the compiler can still perform some optimization given the presence of the linker scoping specifiers.

By using these specifiers, you no longer need to use mapfiles for linker scoping. You can also control the default setting for variable scoping by specifying -xldscope on the command line.

For more information, see A.2.133 -xldscope={v}.

Table 4–1 Linker Scoping Declaration Specifiers




Symbol definitions have global linker scoping and is the least restrictive linker scoping. All references to the symbol bind to the definition in the first dynamic load module that defines the symbol. This linker scoping is the current linker scoping for extern symbols.


Symbol definitions have symbolic linker scoping and is more restrictive than global linker scoping. All references to the symbol from within the dynamic load module being linked bind to the symbol defined within the module. Outside of the module, the symbol appears as though it were global. This linker scoping corresponds to the linker option -Bsymbolic. Although you cannot use -Bsymbolic with C++ libraries, you can use the __symbolic specifier without causing problems. See ld(1) for more information on the linker.


Symbol definitions have hidden linker scoping. Hidden linker scoping is more restrictive than symbolic and global linker scoping. All references within a dynamic load module bind to a definition within that module. The symbol will not be visible outside of the module.

A symbol definition may be redeclared with a more restrictive specifier, but may not be redeclared with a less restrictive specifier. A symbol may not be declared with a different specifier once the symbol has been defined.

__global is the least restrictive scoping, __symbolic is more restrictive, and __hidden is the most restrictive scoping.

All virtual functions must be visible to all compilation units that include the class definition because the declaration of virtual functions affects the construction and interpretation of virtual tables.

You can apply the linker scoping specifiers to struct, class, and union declarations and definitions because C++ classes may require generation of implicit information, such as virtual tables and run-time type information. The specifier, in this case, follows the struct, class, or union keyword. Such an application implies the same linker scoping for all its implicit members.