Setting KRB5_CONFIG is thread safe?

Question

I need to set the path of krb5.conf in my code. Please Let me know which is thread safe ?

Method 1: Set the Environment variable like

setenv("KRB5_CONFIG" ,"/etc/krb5.conf",1);

Method 2:(I am not sure whether this will set the krb5.conf file path)

krb5_set_config_files(krb5_context context,char **filenames);