set environment variant

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how to use C\C++ to set environment variant
i use "putenv()"
it can run but it didn't work(environment variant didn't change)

my code

C++

int main()
{
    char a[128];
    char b[256];

    char all[512];
    cin>>a;
    cin>>b;
    cout<<'\n';
    cout<<a<<'\n';
    cout<<b<<'\n';

    strcpy(all,a);
    strcat(all,"=");
    strcat(all,b);
    cout<<all<<'\n';
    cout<<putenv(all);
}

I try to used function "setenv()" before but the error message:
error: 'setenv' was not declared in this scope
My OS is Windows 7.
IDE Code::block

Posted 9-Jul-13 18:15pm

Ken Chiayuan Chang

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Sergey Alexandrovich Kryukov 10-Jul-13 0:30am

What is "environment variant"? Do you mean "environment variable"?
—SA

2 solutions

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Jochen Arndt · Accepted Answer · 2013-07-09T20:51:00

putenv() changes the environment of the local process (your program). It does not affect the environment of the system.

When a program is started, the system environment is copied to local memory of the process. When using putenv(), the environment in this local memory is changed. This modified environment can be passed to other processes created by spawn(), exec(), or system() from within your program. But when your program terminates, the local copy and all modifications are lost.

«_Superman_» · Accepted Answer · 2013-07-09T21:05:00

Solution 2

What you're doing is the correct way to do it, but it will be applicable only to the current process and possibly its child processes.
When you check the environment variable outside your program, it will show you the old value.

On Windows you can do the same using the SetEnvironmentVariable[^] API.

Posted 9-Jul-13 21:05pm

«_Superman_»

Comments

Jochen Arndt 10-Jul-13 3:11am

+5. I forgot the API call.

H.Brydon 10-Jul-13 17:45pm

Right, +5. You can also create/read/update/delete environment variables using their entries in the registry. You can change your own "User" vars without privs. You will need admin access etc. for system variables.

Ken Chiayuan Chang 11-Jul-13 5:37am

you two are all amazing
thanks you to help me solve my question