-fcommon (-qcommon)

Pragma equivalent

None.

Purpose

Controls where uninitialized global variables are allocated.

When -fcommon (-qcommon) is in effect, uninitialized global variables are allocated in the common section of the object file. When -fno-common (-qnocommon) is in effect, uninitialized global variables are initialized to zero and allocated in the data section of the object file.

Syntax


>>- -f--+-common----+------------------------------------------><
        '-no-common-'


>>- -q--+-common---+-------------------------------------------><
        '-nocommon-'

Defaults

-fcommon (-qcommon) except when -shared (-qmkshrobj) is specified; -fno-common (-qnocommon) when -shared (-qmkshrobj) is specified.
-fno-common (-qnocommon)

Usage

This option does not affect static or automatic variables, or the declaration of structure or union members.

This option is overridden by the common|nocommon and section variable attributes. See The common and nocommon variable attribute and The section variable attribute .

Predefined macros

None.

Examples

In the following declaration, where a and b are global variables:

int a, b;

Compiling with -fcommon (-qcommon) produces the equivalent of the following assembly code:

.comm _a,4
.comm _b,4

Compiling with -fno-common (-qnocommon) produces the equivalent of the following assembly code:

        .globl _a
.data
.zerofill __DATA, __common, _a, 4, 2
        .globl _b
.data
.zerofill __DATA, __common, _b, 4, 2

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