putenv.3

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 3 代码 · 共 72 行

.\" SCCSID: @(#)putenv.3	8.1	9/11/90
.TH putenv 3
.SH Name
putenv \- change or add value to environment 
.SH Syntax
.B int putenv (string)
.br
.B char \(**string;
.SH Description
.NXR "putenv subroutine"
.NXA "getenv subroutine (standard C)" "putenv subroutine"
.NXR "environment" "changing"
The
.I string\^
points to a string of the form
.IB ``name = value.''
The
.PN putenv
subroutine makes the value of the environment variable
.I name\^
equal to
.I value\^
by altering an existing variable or creating a new one.
In either case, the string pointed to by
.I string\^
becomes part of the
environment, so altering the string will change the environment.
The space used by
.I string\^
is no longer used once a new string-defining
.I name\^
is passed to
.PN putenv .
.SH Diagnostics
The
.PN putenv
subroutine returns nonzero if it was unable to obtain enough space
via 
.PN malloc
for an expanded environment, 
otherwise zero.
.SH Warnings
The 
.PN putenv
subroutine manipulates the environment pointed to by 
.PN environ ,
and can be used in conjunction with 
.PN getenv .
However,
.I envp
(the third argument to 
.IR main ) 
is not changed.
.br
This routine uses 
.MS malloc 3
to enlarge the environment.
.br
After
.PN putenv
is called, environmental variables are not in
alphabetical order.
.br
A potential error is to call
.PN putenv
with an automatic variable
as the argument, then exit the calling function while
.I string\^
is still part of the environment.
.SH See Also
execve(2), getenv(3), malloc(3), environ(7)