I am trying to find an equivalent for setenv to use in a C program. What I am trying to do is to modify the values of all the environment variables of the currently running process. I am trying to use putenv but it doesn't change the variables` values in any way. What could I do?
Those are the correct methods for setting the environment variables. The issue you are hitting is that SetEnvironmentVariable which is what is used by the C Runtime setenv does not change system-wide environment variables; only the environment of the currently running process.
Changing the system-wide or per-user environment variables on Windows is normally done using scripts or UI. To modify the system-wide environment variables from a C program, you need (a) to run it with administrator rights, (b) you need to modify the System Registry, and (c) you need to send a WM_SETTINGSCHANGE Win32 message to get the changes picked up by the Windows shell.