Fix a GCC 4.9.2 compiler error in file_util.h.

Author: DavidEGrayson

include/file_util.h

@@ -1,6 +1,7 @@
 // Helpers for opening input and output files.  If the file cannot be opened, an
-// exception is thrown.  For functions with "pipe", if the filename is "-", the
-// standard input or output is used instead of actually opening a file.
+// exception is thrown.  For functions with "pipe" in the name, if the filename
+// is "-", the standard input or output is used instead of actually opening a
+// file.
 
 #pragma once
 
@@ -14,15 +15,16 @@
 
 namespace
 {
-  std::ifstream open_file_input(const std::string & filename)
+  // We would like to just return a std::ifstream here, but that does not
+  // work in GCC 4.9.2 for Raspbian/Debian Jessie.
+  void open_file_input(const std::string & filename, std::ifstream & file)
   {
-    std::ifstream file(filename);
+    file.open(filename);
     if (!file)
     {
       int error_code = errno;
       throw std::runtime_error(filename + ": " + strerror(error_code) + ".");
     }
-    return file;
   }
 
   std::shared_ptr<std::istream> open_file_or_pipe_input(const std::string & filename)
@@ -35,21 +37,22 @@ namespace
     else
     {
       std::ifstream * concrete_file = new std::ifstream();
-      *concrete_file = open_file_input(filename);
+      open_file_input(filename, *concrete_file);
       file.reset(concrete_file);
     }
     return file;
   }
 
-  std::ofstream open_file_output(const std::string & filename)
+  // We would like to just return a std::ifstream here, but that does not
+  // work in GCC 4.9.2 for Raspbian/Debian Jessie.
+  void open_file_output(const std::string & filename, std::ofstream & file)
   {
-    std::ofstream file(filename);
+    file.open(filename);
     if (!file)
     {
       int error_code = errno;
       throw std::runtime_error(filename + ": " + strerror(error_code) + ".");
     }
-    return file;
   }
 
   std::shared_ptr<std::ostream> open_file_or_pipe_output(const std::string & filename)
@@ -62,7 +65,7 @@ namespace
     else
     {
       std::ofstream * concrete_file = new std::ofstream();
-      *concrete_file = open_file_output(filename);
+      open_file_output(filename, *concrete_file);
       file.reset(concrete_file);
     }
     return file;
@@ -71,9 +74,10 @@ namespace
   inline std::string write_string_to_file(const std::string & filename,
     const std::string & contents)
   {
-    auto stream = open_file_output(filename);
-    stream << contents;
-    if (stream.fail())
+    std::ofstream file;
+    open_file_output(filename, file);
+    file << contents;
+    if (file.fail())
     {
       throw std::runtime_error("Failed to write to file.");
     }
@@ -92,13 +96,14 @@ namespace
 
   inline std::string read_string_from_file(const std::string & filename)
   {
-    auto stream = open_file_input(filename);
+    std::ifstream file;
+    open_file_input(filename, file);
     std::string contents =
       std::string(
-        std::istreambuf_iterator<char>(stream),
+        std::istreambuf_iterator<char>(file),
         std::istreambuf_iterator<char>()
       );
-    if (stream.fail())
+    if (file.fail())
     {
       throw std::runtime_error("Failed to read from file.");
     }