From 9aa11b4a003401822f78614272b83427ba08f124 Mon Sep 17 00:00:00 2001
From: Timo Koch <timo.koch@iws.uni-stuttgart.de>
Date: Wed, 15 Aug 2018 02:48:36 +0200
Subject: [PATCH] [io][container] Add optional argument to preallocate memory
 for efficient reading

---
 dumux/io/container.hh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/dumux/io/container.hh b/dumux/io/container.hh
index fd4a17e3af..9d8d68a810 100644
--- a/dumux/io/container.hh
+++ b/dumux/io/container.hh
@@ -52,14 +52,16 @@ void writeContainerToFile(const Container& v,
 /*!
  * \brief Read a simple text file into a container
  * \param filename The filename to write to
+ * \param sizeEstimate an estimate on how many items are there to read into the container
  * \tparam Container  The container type, requires begin(), end(), push_back() method
  *
  * usage: auto v = readFileToContainer<std::vector<double>>("myvector.txt");
  */
 template<typename Container>
-Container readFileToContainer(const std::string& filename)
+Container readFileToContainer(const std::string& filename, std::size_t sizeEstimate = 0)
 {
     Container v;
+    if (sizeEstimate > 0) v.reserve(sizeEstimate); // reserving memory can significantly speed up the reading
     std::ifstream infile(filename, std::ios::in);
     std::istream_iterator<typename Container::value_type> it(infile);
     std::copy(it, std::istream_iterator<typename Container::value_type>(), std::back_inserter(v));
-- 
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