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<li class="toctree-l3"><a class="reference internal" href="#executing-lammps-commands">1.4.3. Executing LAMMPS commands</a></li>
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<li class="toctree-l1"><a class="reference internal" href="Python_head.html">2. Use Python with LAMMPS</a></li>
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<p><span class="math notranslate nohighlight">\(\renewcommand{\AA}{\text{Å}}\)</span></p>
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<section id="using-the-c-api-directly">
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<h1><span class="section-number">1.4.1. </span>Using the C++ API directly<a class="headerlink" href="#using-the-c-api-directly" title="Link to this heading"></a></h1>
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<p>Using the C++ classes of the LAMMPS library is lacking some of the
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convenience of the C library API, but it allows a more direct access to
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simulation data and thus more low-level manipulations and tighter
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integration of LAMMPS into another code. While for the complete C
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library API is provided in the <code class="docutils literal notranslate"><span class="pre">library.h</span></code> header file, for using
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the C++ API it is required to include the individual header files
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defining the individual classes in use. Typically the name of the
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class and the name of the header follow some simple rule. Examples
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are given below.</p>
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</section>
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<section id="creating-or-deleting-a-lammps-object">
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<h1><span class="section-number">1.4.2. </span>Creating or deleting a LAMMPS object<a class="headerlink" href="#creating-or-deleting-a-lammps-object" title="Link to this heading"></a></h1>
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<p>When using the LAMMPS library interfaces, the core task is to create an
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instance of the <a class="reference internal" href="Classes_lammps.html#_CPPv4N9LAMMPS_NS6LAMMPSE" title="LAMMPS_NS::LAMMPS"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">LAMMPS_NS::LAMMPS</span></code></a> class. In C++ this can
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be done directly through the <code class="docutils literal notranslate"><span class="pre">new</span></code> operator. All further operations
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are then initiated through calling member functions of some of the
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components of the LAMMPS class or accessing their data members. The
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destruction of the LAMMPS instance is correspondingly initiated by using
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the <code class="docutils literal notranslate"><span class="pre">delete</span></code> operator. Here is a simple example:</p>
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<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"lammps.h"</span>
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<span class="cp">#include</span><span class="w"> </span><span class="cpf"><mpi.h></span>
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<span class="cp">#include</span><span class="w"> </span><span class="cpf"><iostream></span>
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<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="n">argv</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="w"> </span><span class="n">LAMMPS_NS</span><span class="o">::</span><span class="n">LAMMPS</span><span class="w"> </span><span class="o">*</span><span class="n">lmp</span><span class="p">;</span>
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<span class="w"> </span><span class="c1">// custom argument vector for LAMMPS library</span>
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<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">lmpargv</span><span class="p">[]</span><span class="w"> </span><span class="p">{</span><span class="s">"liblammps"</span><span class="p">,</span><span class="w"> </span><span class="s">"-log"</span><span class="p">,</span><span class="w"> </span><span class="s">"none"</span><span class="p">};</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">lmpargc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="n">lmpargv</span><span class="p">)</span><span class="o">/</span><span class="k">sizeof</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">);</span>
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<span class="w"> </span><span class="c1">// explicitly initialize MPI</span>
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<span class="w"> </span><span class="n">MPI_Init</span><span class="p">(</span><span class="o">&</span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">argv</span><span class="p">);</span>
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<span class="w"> </span><span class="c1">// create LAMMPS instance</span>
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<span class="w"> </span><span class="n">lmp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">LAMMPS_NS</span><span class="o">::</span><span class="n">LAMMPS</span><span class="p">(</span><span class="n">lmpargc</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="p">)</span><span class="n">lmpargv</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_COMM_WORLD</span><span class="p">);</span>
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<span class="w"> </span><span class="c1">// output numerical version string</span>
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<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"LAMMPS version ID: "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">lmp</span><span class="o">-></span><span class="n">num_ver</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">endl</span><span class="p">;</span>
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<span class="w"> </span><span class="c1">// delete LAMMPS instance</span>
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<span class="w"> </span><span class="k">delete</span><span class="w"> </span><span class="n">lmp</span><span class="p">;</span>
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<span class="w"> </span><span class="c1">// stop MPI environment</span>
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<span class="w"> </span><span class="n">MPI_Finalize</span><span class="p">();</span>
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<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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<p>This minimal example only requires to include the <code class="docutils literal notranslate"><span class="pre">lammps.h</span></code> header
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file since it only accesses a non-pointer member of the LAMMPS class.</p>
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</section>
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<section id="executing-lammps-commands">
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<h1><span class="section-number">1.4.3. </span>Executing LAMMPS commands<a class="headerlink" href="#executing-lammps-commands" title="Link to this heading"></a></h1>
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<p>Once a LAMMPS instance is created by your C++ code, you need to set up a
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simulation and that is most conveniently done by “driving” it through
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issuing commands like you would do when running a LAMMPS simulation from
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an input script. Processing of input in LAMMPS is handled by the
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<a class="reference internal" href="Classes_input.html#_CPPv4N9LAMMPS_NS5InputE" title="LAMMPS_NS::Input"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">Input</span></code></a> class an instance of which is a
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member of the <a class="reference internal" href="Classes_lammps.html#_CPPv4N9LAMMPS_NS6LAMMPSE" title="LAMMPS_NS::LAMMPS"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">LAMMPS</span></code></a> class. You have
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two options: reading commands from a file, or executing a single
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command from a string. See below for a small example:</p>
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<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"lammps.h"</span>
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<span class="cp">#include</span><span class="w"> </span><span class="cpf">"input.h"</span>
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<span class="cp">#include</span><span class="w"> </span><span class="cpf"><mpi.h></span>
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<span class="k">using</span><span class="w"> </span><span class="k">namespace</span><span class="w"> </span><span class="nn">LAMMPS_NS</span><span class="p">;</span>
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<span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="n">argv</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">lmpargv</span><span class="p">[]</span><span class="w"> </span><span class="p">{</span><span class="s">"liblammps"</span><span class="p">,</span><span class="w"> </span><span class="s">"-log"</span><span class="p">,</span><span class="w"> </span><span class="s">"none"</span><span class="p">};</span>
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<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">lmpargc</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">sizeof</span><span class="p">(</span><span class="n">lmpargv</span><span class="p">)</span><span class="o">/</span><span class="k">sizeof</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="p">);</span>
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<span class="w"> </span><span class="n">MPI_Init</span><span class="p">(</span><span class="o">&</span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="o">&</span><span class="n">argv</span><span class="p">);</span>
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<span class="w"> </span><span class="n">LAMMPS</span><span class="w"> </span><span class="o">*</span><span class="n">lmp</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">new</span><span class="w"> </span><span class="n">LAMMPS</span><span class="p">(</span><span class="n">lmpargc</span><span class="p">,</span><span class="w"> </span><span class="p">(</span><span class="kt">char</span><span class="w"> </span><span class="o">**</span><span class="p">)</span><span class="n">lmpargv</span><span class="p">,</span><span class="w"> </span><span class="n">MPI_COMM_WORLD</span><span class="p">);</span>
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<span class="w"> </span><span class="n">lmp</span><span class="o">-></span><span class="n">input</span><span class="o">-></span><span class="n">file</span><span class="p">(</span><span class="s">"in.melt"</span><span class="p">);</span>
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<span class="w"> </span><span class="n">lmp</span><span class="o">-></span><span class="n">input</span><span class="o">-></span><span class="n">one</span><span class="p">(</span><span class="s">"run 100 post no"</span><span class="p">);</span>
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<span class="w"> </span><span class="k">delete</span><span class="w"> </span><span class="n">lmp</span><span class="p">;</span>
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<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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