Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for a snapshot of the master branch, built from commit bd78d4d549.
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Global env

boost::process::env

Synopsis

// In header: <boost/process/env.hpp>

unspecified env;

Description

The env property provides a functional way to modify the environment used by the child process. If none is passed the environment is inherited from the father process. Appending means that the environment will be interpreted as a ';' or ':' separated list as used in PATH.

On both posix and windows the environment variables can be lists of strings, separated by ';'. This is typically used for the PATH variable.

By default the environment will be inherited from the launching process, which is also true if environment are modified with this initializer.

Details

Operations

Setting variables

To set a variable id the value value the following syntax can be used.

env[id] = value;
env(id, value);

std::initializer_list is among the allowed types, so the following syntax is also possible.

env[id] = {value1, value2};
env(id, {value1, value2});
[Note] Note

Creates the variable if it does not exist.

The following lists contain possible value types, with char_type being either char or wchar_t for both id and value.

id
  • std::basic_string<char_type>

  • const char_type *

value
  • std::basic_string<char_type>

  • const char_type *

  • std::initializer_list<const char_type *>

  • std::vector<std::basic_string<char_type>>

[Note] Note

Using std::vector or std::initializer_list

Append variables

Appending means, that a variable will be interpreted as a To append a variable id the value value the following syntax can be used:

env[id] += value;

std::initializer_list is among the allowed types, so the following syntax is also possible.

env[id] += {value1, value2};
[Note] Note

Creates the variable if it does not exist.

The following lists contain possible value types, with char_type being either char or wchar_t for both id and value.

id
  • std::basic_string<char_type>

  • const char_type *

value
  • std::basic_string<char_type>

  • const char_type *

  • std::initializer_list<const char_type *>

  • std::vector<std::basic_string<char_type>>

Reset variables

Reseting signle variables can be done in the following way:

env[id] = boost::none;
env(id, boost::none);
[Note] Note

This does not set the value empty, but removes it from the list.

The following lists contain possible value types, with char_type being either char or wchar_t:

id
  • std::basic_string<char_type>

  • const char_type *

Initialize the environment

The whole environment can be initialized from an object of type boost::process::environment

env=env;
env(env);
[Note] Note

The passed environment can also be default-constructed to get an empty environment.

id
  • std::basic_string<char_type>

  • const char_type *

Example

spawn("b2", env["PATH"]+="F:/boost", env["SOME_VAR"]=boost::none, env["NEW_VAR"]="VALUE");

If the overload style should be done by passing an instance of boost::process::environment the above example would look like this.

environment e = this_process::environment();
e["PATH"]   += "F:/boost";
e.erase("SOME_VAR");
e["NEW_VAR"] = "VALUE";
spawn("b2", e);
[Warning] Warning

Passing an empty environment will cause undefined behaviour.


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