string solutionFile="the solution file";FileInfo fInfo = new FileInfo(solutionFile);
        string solutionText = File.ReadAllText(solutionFile);
        Regex reg = new Regex("Project\("[^"]+"\) = "[^"]+", "([^"]+)", "[^"]+"");
        MatchCollection mc = reg.Matches(solutionText);
        List<string> files = new List<string>();
        foreach (Match m in mc)
        {
            string project_file = m.Groups[1].Value;
            project_file = System.IO.Path.Combine(fInfo.Directory.FullName, project_file);
            if (System.IO.File.Exists(project_file))
            {
                string project_path = new FileInfo(project_file).DirectoryName;
                XmlDocument doc = new XmlDocument();
                doc.Load(project_file);
                XmlNamespaceManager ns = new XmlNamespaceManager(doc.NameTable);
                ns.AddNamespace("ms", "http://schemas.microsoft.com/developer/msbuild/2003");
                System.Xml.XmlNodeList list = doc.ChildNodes[1].SelectNodes("//ms:ItemGroup/ms:Compile", ns);
                foreach (XmlNode node in list)
                {
                    files.Add(Path.Combine(project_path, node.Attributes["Include"].InnerText));
                }
            }
        }