From daf22630190c43a8d5a5c61541de7b2cb387c2e6 Mon Sep 17 00:00:00 2001
From: Ivan Smirnov <ifsmirnov@yandex.ru>
Date: Mon, 5 Feb 2018 20:09:45 +0300
Subject: [PATCH] Do not print newline after graphs with no edges

---
 impl/generic_graph_inl.h | 21 +++++++++++++++++++--
 jngen.h                  | 21 +++++++++++++++++++--
 tests/graph.cpp          | 33 +++++++++++++++++++++++++++++++++
 3 files changed, 71 insertions(+), 4 deletions(-)

diff --git a/impl/generic_graph_inl.h b/impl/generic_graph_inl.h
index b020cdc..2c3fd97 100644
--- a/impl/generic_graph_inl.h
+++ b/impl/generic_graph_inl.h
@@ -213,24 +213,41 @@ void GenericGraph::addEdge(int u, int v, const Weight& w) {
 void GenericGraph::doPrintEdges(
     std::ostream& out, const OutputModifier& mod) const
 {
+    bool pendingEndline = false;
     if (mod.printN) {
         out << n();
         if (mod.printM) {
             out << " " << m();
         }
-        out << "\n";
+        pendingEndline = true;
     } else if (mod.printM) {
-        out << m() << "\n";
+        out << m();
+        pendingEndline = true;
+    }
+
+    if (n() == 0) {
+        return;
     }
 
     if (vertexWeights_.hasNonEmpty()) {
         auto vertexWeights = prepareWeightArray(vertexWeights_, n());
+        if (pendingEndline) {
+            out << "\n";
+        }
         for (int i = 0; i < n(); ++i) {
             if (i > 0) {
                 out << " ";
             }
             JNGEN_PRINT_NO_MOD(vertexWeights[vertexByLabel(i)]);
         }
+        pendingEndline = true;
+    }
+
+    if (m() == 0) {
+        return;
+    }
+
+    if (pendingEndline) {
         out << "\n";
     }
 
diff --git a/jngen.h b/jngen.h
index 7b4de07..dc2eb31 100644
--- a/jngen.h
+++ b/jngen.h
@@ -5902,24 +5902,41 @@ void GenericGraph::addEdge(int u, int v, const Weight& w) {
 void GenericGraph::doPrintEdges(
     std::ostream& out, const OutputModifier& mod) const
 {
+    bool pendingEndline = false;
     if (mod.printN) {
         out << n();
         if (mod.printM) {
             out << " " << m();
         }
-        out << "\n";
+        pendingEndline = true;
     } else if (mod.printM) {
-        out << m() << "\n";
+        out << m();
+        pendingEndline = true;
+    }
+
+    if (n() == 0) {
+        return;
     }
 
     if (vertexWeights_.hasNonEmpty()) {
         auto vertexWeights = prepareWeightArray(vertexWeights_, n());
+        if (pendingEndline) {
+            out << "\n";
+        }
         for (int i = 0; i < n(); ++i) {
             if (i > 0) {
                 out << " ";
             }
             JNGEN_PRINT_NO_MOD(vertexWeights[vertexByLabel(i)]);
         }
+        pendingEndline = true;
+    }
+
+    if (m() == 0) {
+        return;
+    }
+
+    if (pendingEndline) {
         out << "\n";
     }
 
diff --git a/tests/graph.cpp b/tests/graph.cpp
index 6a22118..1ca0d08 100644
--- a/tests/graph.cpp
+++ b/tests/graph.cpp
@@ -117,4 +117,37 @@ BOOST_AUTO_TEST_CASE(various_traits) {
     }
 }
 
+BOOST_AUTO_TEST_CASE(empty_output) {
+    setMod().reset();
+
+    std::stringstream ss;
+
+    ss << Graph::random(10, 0).g().printN().printM().add1() << std::endl;
+    BOOST_TEST(ss.str() == "10 0\n");
+    ss.str("");
+
+    ss << Graph::random(10, 0).g().printN().add1() << std::endl;
+    BOOST_TEST(ss.str() == "10\n");
+    ss.str("");
+
+    Graph g = Graph::random(10, 0);
+    g.setVertexWeights(Array::random(g.n(), 10, 20));
+    ss << g.printN().printM() << std::endl;
+    auto s = ss.str();
+    s.pop_back();
+    BOOST_TEST(s != "\n");
+    ss.str("");
+
+    g = Graph::empty(5);
+    g.setVertexWeights(Array::id(5));
+    ss << g << std::endl;
+    BOOST_TEST(ss.str() == "0 1 2 3 4\n");
+    ss.str("");
+
+    g = Graph::empty(0);
+    ss << g.printN().printM() << std::endl;
+    BOOST_TEST(ss.str() == "0 0\n");
+    ss.str("");
+}
+
 BOOST_AUTO_TEST_SUITE_END()