How do I export a environmental variable to a C program?

In article <5eca7cf1-8080-4625-b2c1-383808d530b7@b1g2000hsg.googlegroups.com>, iavian <vijay@iavian.com> wrote: >Hi all , > >I want to set a env variable in a C program? . Not through shell env >variables. Any help? How an environment variable gets set is beyond the scope of the C language. They're typically assigned through an OS-defined mechanism when the process is created. A newsgroup whose scope includes how to start processes on your OS may be able to provide more specific guidance. Many C implementations also provide extensions that allow environment variables to be set from within the program. Your implementation's documentation may shed some light on that. dave -- Dave Vandervies dj3vande at eskimo dot com He'll be buried face down, nine edge first. Unlike most people of whom that is said, in his case, it's a compliment. --Richard Bos, on John Backus, in comp.lang.c

On 9 May 2008 at 17:26, iavian wrote: > I want to set a env variable in a C program? . Not through shell env > variables. Any help? What do you mean "not through shell env variables"? If you're on a POSIX system, check out setenv() and putenv().

In article <5eca7cf1-8080-4625-b2c1-383808d530b7@b1g2000hsg.googlegroups.com>, iavian <vijay@iavian.com> wrote: >I want to set a env variable in a C program? . Not through shell env >variables. Any help? C does not provide any mechanism to set environment variables. It is common for OSes to provide a setenv() routine in their libraries. Note that when OSes do so provide, often setenv() only affects the environment of the running program and any programs that it invokes after that point, such as by system() or by OS routines such as exec*() . Unix-like systems often have *no* mechanism that would allow a program to change the environment variables of other programs that are already running. -- "All is vanity." -- Ecclesiastes

iavian <vijay@iavian.com> wrote: > I want to set a env variable in a C program? . Not through shell env > variables. Any help? This is not a C question since this only depends on how your shell handles things. But, that out of the way, you simply can't do that (at least with no shell I ever heard of). Your C program is a process started by your shell and such a child- process can never change anything in its "parent" process. The only thing you can do is to have the the program output something the shell then explicitely executes, like (e.g. using bash): ---- env_cmd.c ----- #include <stdio.h> int main( void ) { puts( "export X=AAA" ); return 0; } -------------------- and then do e.g. > gcc -o env_cmd env_cmd.c > `./env_cmd` # note the backticks > echo $X AAA Regards, Jens -- \ Jens Thoms Toerring ___ jt@toerring.de \__________________________ http://toerring.de

jt@toerring.de (Jens Thoms Toerring) writes: > iavian <vijay@iavian.com> wrote: >> I want to set a env variable in a C program? . Not through shell env >> variables. Any help? > > This is not a C question since this only depends on how your > shell handles things. But, that out of the way, you simply > can't do that (at least with no shell I ever heard of). Your > C program is a process started by your shell and such a child- > process can never change anything in its "parent" process. The OP didn't seem to be asking about propagating the setting to the parent process (assuming that "parent process" is meaningful). As far as I can tell, the POSIX setenv() function (not standard C) would satisfy the requirement he stated. Whether it would satisfy his actual requirement is another question. <OT>In Unix-like systems, there are various ways for a process to set one of its own environment variables in response to information from a child process. You demonstrated one of them in part of your article that I ruthlessly snipped; other ways are possible. comp.unix.programmer would be a better place to discuss it -- after checking any FAQ lists, since this kind of question comes up frequently.</OT> -- Keith Thompson (The_Other_Keith) <kst-u@mib.org> Nokia "We must do something. This is something. Therefore, we must do this." -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thanks for all who replied .. I am writing a function for postgres in C which connect to Oracle db .. postgres accepts a shared object to be loaded . So, when the .so is loaded inside postgres , .so could find oracle environments.. I am not sure what should be the best way to do it .. whenever a row is inserted in postgres , a trigger will call this C function which connects to oracle and inserts the record in Oracle db Any pointers? My problem is On May 9, 2:52 pm, Keith Thompson <ks...@mib.org> wrote: > j...@toerring.de (Jens Thoms Toerring) writes: > > > iavian <vi...@iavian.com> wrote: > >> I want to set a env variable in a C program? . Not through shell env > >> variables. Any help? > > > This is not a C question since this only depends on how your > > shell handles things. But, that out of the way, you simply > > can't do that (at least with no shell I ever heard of). Your > > C program is a process started by your shell and such a child- > > process can never change anything in its "parent" process. > > The OP didn't seem to be asking about propagating the setting to the > parent process (assuming that "parent process" is meaningful). As far > as I can tell, the POSIX setenv() function (not standard C) would > satisfy the requirement he stated. Whether it would satisfy his > actual requirement is another question. > > <OT>In Unix-like systems, there are various ways for a process to set > one of its own environment variables in response to information from a > child process. You demonstrated one of them in part of your article > that I ruthlessly snipped; other ways are possible. > comp.unix.programmer would be a better place to discuss it -- after > checking any FAQ lists, since this kind of question comes up > frequently.</OT> > > -- > Keith Thompson (The_Other_Keith) <ks...@mib.org> > Nokia > "We must do something. This is something. Therefore, we must do this." > -- Antony Jay and Jonathan Lynn, "Yes Minister"

iavian wrote: > > I am writing a function for postgres in C which connect to Oracle > db .. postgres accepts a shared object to be loaded . So, when the > .so is loaded inside postgres , .so could find oracle environments.. > I am not sure what should be the best way to do it .. > > whenever a row is inserted in postgres , a trigger will call this C > function which connects to oracle and inserts the record in Oracle db Top-posting has lost all connection to previous traffic in this thread. It was totally unnecessary. Please do not top-post. Your answer belongs after (or intermixed with) the quoted material to which you reply, after snipping all irrelevant material. See the following links: <http://www.catb.org/~esr/faqs/smart-questions.html> <http://www.caliburn.nl/topposting.html> <http://www.netmeister.org/news/learn2quote.html> <http://cfaj.freeshell.org/google/> (taming google) <http://members.fortunecity.com/nnqweb/> (newusers) -- [mail]: Chuck F (cbfalconer at maineline dot net) [page]: <http://cbfalconer.home.att.net> Try the download section. ** Posted from http://www.teranews.com **

iavian <vijay@iavian.com> writes: > I am writing a function for postgres in C which connect to Oracle > db .. postgres accepts a shared object to be loaded . So, when the .so > is loaded inside postgres , .so could find oracle environments.. I am > not sure what should be the best way to do it .. > > whenever a row is inserted in postgres , a trigger will call this C > function which connects to oracle and inserts the record in Oracle db > > Any pointers? I think you've already been advised to ask in comp.unix.programmer (I assume you're using a Unix-like system). That's the best advice you're going to get here. -- Keith Thompson (The_Other_Keith) <kst-u@mib.org> Nokia "We must do something. This is something. Therefore, we must do this." -- Antony Jay and Jonathan Lynn, "Yes Minister"

On Fri, 9 May 2008 10:26:48 -0700 (PDT), iavian <vijay@iavian.com> wrote in comp.lang.c: > Hi all , > > I want to set a env variable in a C program? . Not through shell env > variables. Any help? The standard C library does not provide any functions to set environment variables, just one to search for and read them. All of today's most popular operating systems provided their own system-specific extensions for doing this. You need to ask in a group that supports your particular compiler/OS combination for details. -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://c-faq.com/ comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ http://www.club.cc.cmu.edu/~ajo/docs/FAQ-acllc.html