1、环境变量获取和设置定义参考：
base\environment.h
base\environment.cc
// Copyright 2011 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_ENVIRONMENT_H_
#define BASE_ENVIRONMENT_H_
#include <map>
#include <memory>
#include <string>
#include "base/base_export.h"
#include "base/strings/string_piece.h"
#include "build/build_config.h"
namespace base {
namespace env_vars {
#if BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
BASE_EXPORT extern const char kHome[];
#endif
} // namespace env_vars
class BASE_EXPORT Environment {
public:
virtual ~Environment();
// Returns the appropriate platform-specific instance.
static std::unique_ptr<Environment> Create();
// Gets an environment variable's value and stores it in |result|.
// Returns false if the key is unset.
virtual bool GetVar(StringPiece variable_name, std::string* result) = 0;
// Syntactic sugar for GetVar(variable_name, nullptr);
virtual bool HasVar(StringPiece variable_name);
// Returns true on success, otherwise returns false. This method should not
// be called in a multi-threaded process.
virtual bool SetVar(StringPiece variable_name,
const std::string& new_value) = 0;
// Returns true on success, otherwise returns false. This method should not
// be called in a multi-threaded process.
virtual bool UnSetVar(StringPiece variable_name) = 0;
};
#if BUILDFLAG(IS_WIN)
using NativeEnvironmentString = std::wstring;
#elif BUILDFLAG(IS_POSIX) || BUILDFLAG(IS_FUCHSIA)
using NativeEnvironmentString = std::string;
#endif
using EnvironmentMap =
std::map<NativeEnvironmentString, NativeEnvironmentString>;
} // namespace base
#endif // BASE_ENVIRONMENT_H_
二、例子：
以获取SSLKEYLOGFILE环境变量为例：
std::unique_ptr<base::Environment> env(base::Environment::Create());
std::string env_str;
if (env->GetVar("SSLKEYLOGFILE", &env_str)){
}