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    <p>I simply did a quick performance measurement with the following code and </p> <pre><code>v1.insert( v1.end(), v2.begin(), v2.end() ); </code></pre> <p>seems to be the right choice (as already stated above). Nevertheless, you find the reported performance below.</p> <p>Test code:</p> <pre><code>#include &lt;vector&gt; #include &lt;string&gt; #include &lt;boost/timer/timer.hpp&gt; //============================================================================== // //============================================================================== /// Returns a vector containing the sequence [ 0, ... , n-1 ]. inline std::vector&lt;int&gt; _range(const int n) { std::vector&lt;int&gt; tmp(n); for(int i=0; i&lt;n; i++) tmp[i] = i; return tmp; } void test_perf_vector_append() { const vector&lt;int&gt; testdata1 = _range(100000000); const vector&lt;int&gt; testdata2 = _range(100000000); vector&lt;int&gt; testdata; printf("--------------------------------------------------------------\n"); printf(" METHOD: push_back()\n"); printf("--------------------------------------------------------------\n"); testdata.clear(); { vector&lt;int&gt;().swap(testdata); } testdata = testdata1; { boost::timer::auto_cpu_timer t; for(size_t i=0; i&lt;testdata2.size(); i++) { testdata.push_back(testdata2[i]); } } printf("--------------------------------------------------------------\n"); printf(" METHOD: reserve() + push_back()\n"); printf("--------------------------------------------------------------\n"); testdata.clear(); { vector&lt;int&gt;().swap(testdata); } testdata = testdata1; { boost::timer::auto_cpu_timer t; testdata.reserve(testdata.size() + testdata2.size()); for(size_t i=0; i&lt;testdata2.size(); i++) { testdata.push_back(testdata2[i]); } } printf("--------------------------------------------------------------\n"); printf(" METHOD: insert()\n"); printf("--------------------------------------------------------------\n"); testdata.clear(); { vector&lt;int&gt;().swap(testdata); } testdata = testdata1; { boost::timer::auto_cpu_timer t; testdata.insert( testdata.end(), testdata2.begin(), testdata2.end() ); } printf("--------------------------------------------------------------\n"); printf(" METHOD: reserve() + insert()\n"); printf("--------------------------------------------------------------\n"); testdata.clear(); { vector&lt;int&gt;().swap(testdata); } testdata = testdata1; { boost::timer::auto_cpu_timer t; testdata.reserve( testdata.size() + testdata.size() ); testdata.insert( testdata.end(), testdata2.begin(), testdata2.end() ); } printf("--------------------------------------------------------------\n"); printf(" METHOD: copy() + back_inserter()\n"); printf("--------------------------------------------------------------\n"); testdata.clear(); { vector&lt;int&gt;().swap(testdata); } testdata = testdata1; { boost::timer::auto_cpu_timer t; testdata.reserve(testdata.size() + testdata2.size()); copy(testdata2.begin(), testdata2.end(), back_inserter(testdata)); } printf("--------------------------------------------------------------\n"); printf(" METHOD: reserve() + copy() + back_inserter()\n"); printf("--------------------------------------------------------------\n"); testdata.clear(); { vector&lt;int&gt;().swap(testdata); } testdata = testdata1; { boost::timer::auto_cpu_timer t; testdata.reserve(testdata.size() + testdata2.size()); copy(testdata2.begin(), testdata2.end(), back_inserter(testdata)); } } </code></pre> <p>With Visual Studio 2008 SP1, x64, Release mode, /O2 /LTCG the output is as follows:</p> <pre><code>-------------------------------------------------------------- METHOD: push_back() -------------------------------------------------------------- 0.933077s wall, 0.577204s user + 0.343202s system = 0.920406s CPU (98.6%) -------------------------------------------------------------- METHOD: reserve() + push_back() -------------------------------------------------------------- 0.612753s wall, 0.452403s user + 0.171601s system = 0.624004s CPU (101.8%) -------------------------------------------------------------- METHOD: insert() -------------------------------------------------------------- 0.424065s wall, 0.280802s user + 0.140401s system = 0.421203s CPU (99.3%) -------------------------------------------------------------- METHOD: reserve() + insert() -------------------------------------------------------------- 0.637081s wall, 0.421203s user + 0.218401s system = 0.639604s CPU (100.4%) -------------------------------------------------------------- METHOD: copy() + back_inserter() -------------------------------------------------------------- 0.743658s wall, 0.639604s user + 0.109201s system = 0.748805s CPU (100.7%) -------------------------------------------------------------- METHOD: reserve() + copy() + back_inserter() -------------------------------------------------------------- 0.748560s wall, 0.624004s user + 0.124801s system = 0.748805s CPU (100.0%) </code></pre>
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    1. POWhat is the most efficient way to append one std::vector to the end of another?
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    1. USStefan
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    1. COWonderful answer!
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