Jeff Garland wrote:
On Sun, 16 Jan 2005 21:05:55 -0600, Aaron W. LaFramboise wrote
Is there a Boost library that supports manipulating process environment variables?
I think there was some discussion of integrating this capability into the program options library, but it may be a 'planned extension' as it isn't in the current docs that I could find.
It's present in the 1.32 version as the function 'parse_environment_variables'. I'm not sure if that's what Aaron wanted so here's the docs (they were added after 1.32 and I don't know where's CVS Boost.Book-generated docs now). <title>Environment variables</title> <para><firstterm>Environment variables</firstterm> are string variables which are available to all programs via the <code>getenv</code> function of C runtime library. The operating system allows to set initial values for a given user, and the values can be further changed on the command line. For example, on Windows one can use the <filename>autoexec.bat</filename> file or (on recent versions) the <filename>Control Panel/System/Advanced/Environment Variables</filename> dialog, and on Unix —, the <filename>/etc/profile</filename>, <filename>~/profile</filename> and <filename>~/bash_profile</filename> files. Because environment variables can be set for the entire system, they are particularly suitable for options which apply to all programs. </para> <para>The environment variables can be parsed with the &parse_environment; function. The function have several overloaded versions. The first parameter is always an &options_description; instance, and the second specifies what variables must be processed, and what option names must correspond to it. To describe the second parameter we need to consider naming conventions for environment variables.</para> <para>If you have an option that should be specified via environment variable, you need make up the variable's name. To avoid name clashes, we suggest that you use a sufficiently unique prefix for environment variables. Also, while option names are most likely in lower case, environment variables conventionally use upper case. So, for an option name <literal>proxy</literal> the environment variable might be called <envar>BOOST_PROXY</envar>. During parsing, we need to perform reverse conversion of the names. This is accomplished by passing the choosen prefix as the second parameter of the &parse_environment; function. Say, if you pass <literal>BOOST_</literal> as the prefix, and there are two variables, <envar>CVSROOT</envar> and <envar>BOOST_PROXY</envar>, the first variable will be ignored, and the second one will be converted to option <literal>proxy</literal>. </para> <para>The above logic is sufficient in many cases, but it is also possible to pass, as the second parameter of the &parse_environment; function, any function taking a <code>std::string</code> and returning <code>std::string</code>. That function will be called for each environment variable and should return either the name of the option, or empty string if the variable should be ignored. </para> - Volodya