fvisibility

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

IDE Equivalent

None

Architectures

All

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.
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=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

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

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.