fvisibility

Specifies the default visibility for global symbols or the visibility for symbols in a file.

Syntax

Linux and OS X:

-fvisibility=keyword

-fvisibility-keyword=filename

Windows:

None

Arguments

keyword

Specifies the visibility setting. Possible values are:

default	Sets visibility to default.
extern	Sets visibility to extern.
hidden	Sets visibility to hidden.
internal	Sets visibility to internal.
protected	Sets visibility to protected. This value is not available on OS X* systems.

filename

Is the pathname of a file containing the list of symbols whose visibility you want to set. The symbols must be separated by whitespace (spaces, tabs, or newlines).

Default

-fvisibility=default

The compiler sets visibility of symbols to default.

Description

This option specifies the default visibility for global symbols (syntax -fvisibility=keyword) or the visibility for symbols in a file (syntax -fvisibility-keyword=filename).

Visibility specified by -fvisibility-keyword=filename overrides visibility specified by -fvisibility=keyword for symbols specified in a file.

Option	Description
-fvisibility=default -fvisibility-default`=filename`	Sets visibility of symbols to default. This means other components can reference the symbol, and the symbol definition can be overridden (preempted) by a definition of the same name in another component.
-fvisibility=extern -fvisibility-extern`=filename`	Sets visibility of symbols to extern. This means the symbol is treated as though it is defined in another component. It also means that the symbol can be overridden by a definition of the same name in another component.
-fvisibility=hidden -fvisibility-hidden`=filename`	Sets visibility of symbols to hidden. This means that other components cannot directly reference the symbol. However, its address may be passed to other components indirectly.
-fvisibility=internal -fvisibility-internal`=filename`	Sets visibility of symbols to internal. This means that the symbol cannot be referenced outside its defining component, either directly or indirectly. The affected functions can never be called from another module, including through function pointers.
-fvisibility=protected -fvisibility-protected`=filename`	Sets visibility of symbols to protected. This means other components can reference the symbol, but it cannot be overridden by a definition of the same name in another component. This value is not available on OS X* systems.

If an -fvisibility option is specified more than once on the command line, the last specification takes precedence over any others.

If a symbol appears in more than one visibility filename, the setting with the least visibility takes precedence.

The following shows the precedence of the visibility settings (from greatest to least visibility):

extern
default
protected
hidden
internal

Note that extern visibility only applies to functions. If a variable symbol is specified as extern, it is assumed to be default.

IDE Equivalent

Visual Studio: None

Eclipse: Data > Default Symbol Visibility

Xcode: None

Alternate Options

None

Example

A file named prot.txt contains symbols a, b, c, d, and e. Consider the following:

-fvisibility-protected=prot.txt

This option sets protected visibility for all the symbols in the file. It has the same effect as specifying fvisibility=protected in the declaration for each of the symbols.