Site updated: 2018-06-28 21:52:01

Author: oceanoverflow

2018/06/26/CGO/index.html

@@ -13,7 +13,7 @@
 <meta property="og:site_name" content="Whyyy">
 <meta property="og:description" content="cgo is an amazing technology which allows Go programs to interoperate with C libraries. Given a Go source file written with some special features, cgo outputs Go and C files that can be combined into">
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-<meta property="og:updated_time" content="2018-06-26T08:57:04.482Z">
+<meta property="og:updated_time" content="2018-06-28T13:51:20.929Z">
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 <meta name="twitter:title" content="CGO">
 <meta name="twitter:description" content="cgo is an amazing technology which allows Go programs to interoperate with C libraries. Given a Go source file written with some special features, cgo outputs Go and C files that can be combined into">
@@ -103,11 +103,14 @@ <h1 class="article-title" itemprop="name">
 <h2 id="cgo-directives"><a href="#cgo-directives" class="headerlink" title="cgo directives"></a>cgo directives</h2><figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// #include &lt;stdio.h&gt;</span></span><br><span class="line"><span class="comment">// #include &lt;errno.h&gt;</span></span><br><span class="line"><span class="keyword">import</span> <span class="string">"C"</span></span><br></pre></td></tr></table></figure>
 <p>CFLAGS, CPPFLAGS, CXXFLAGS, FFLAGS, LDFLAGS may be defined with pseudo <code>#cgo</code> directives within these comments to tweak the behavior of the C, C++ or Fortran compiler. Values defined in multiple directives are concatenated together. The directive can include a list of build constraints limiting its effect to systems satisfying one of the constraints.</p>
 <p>cgo recognizes this comment. Any lines starting with <code>#cgo</code> followed by a space character are removed; these become directives for cgo. The remaining lines are used as a header when compiling the C parts of the package. In this case those lines are just a single <code>#include</code> statement, but they can be almost any C code. The <code>cgo</code> directives are used to provide flags for the compiler and linker when building the C parts of the package.</p>
-<figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// #cgo CFLAGS: -DPNG_DEBUG=1</span></span><br><span class="line"><span class="comment">// #cgo amd64 386 CF:AGS: -D86=1</span></span><br><span class="line"><span class="comment">// #cgo LDFLAGS: -lpng</span></span><br><span class="line"><span class="comment">// #include &lt;png.h&gt;</span></span><br><span class="line"><span class="keyword">import</span> <span class="string">"C"</span></span><br></pre></td></tr></table></figure>
+<figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// #cgo CFLAGS: -DPNG_DEBUG=1</span></span><br><span class="line"><span class="comment">// #cgo amd64 386 CFLAGS: -D86=1</span></span><br><span class="line"><span class="comment">// #cgo LDFLAGS: -lpng</span></span><br><span class="line"><span class="comment">// #include &lt;png.h&gt;</span></span><br><span class="line"><span class="keyword">import</span> <span class="string">"C"</span></span><br></pre></td></tr></table></figure>
 <p>Alternatively, CPPFLAGS and LDFLAGS may be obtained via the pkg-config tool using a ‘#cgo pkg-config:’ directive followed by the package names. For example:</p>
 <figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// #cgo pkg-config: png cairo</span></span><br><span class="line"><span class="comment">// #include &lt;png.h&gt;</span></span><br><span class="line"><span class="keyword">import</span> <span class="string">"C"</span></span><br></pre></td></tr></table></figure>
 <figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// #cgo LDFLAGS -L$&#123;SRCDIR&#125;/libs -l foo</span></span><br></pre></td></tr></table></figure>
 <figure class="highlight golang"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// #cgo LDFLAGS -L/go/src/foo/libs -l foo</span></span><br></pre></td></tr></table></figure>
+<p><code>-L</code> is the path to the directories containing the libraries. A search path for libraries.<br><code>-l</code> is the name of the library you want to link to.</p>
+<p>For instance, if you want to link to the library  <code>~/libs/libabc.a</code>  you’d add:</p>
+<figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line">-L$(HOME)/libs -labc</span><br></pre></td></tr></table></figure>
 <figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">| file                            | compiler          |</span><br><span class="line">| ------------------------------- |:-----------------:|</span><br><span class="line">| xxx.c, xxx.s, xxx.S             | C compiler        |</span><br><span class="line">| xxx.cc, xxx.cpp, xxx.cxx        | C++ compiler      |</span><br><span class="line">| xxx.f, xxx.F, xxx.for, xxx.f90  | fortran compiler  |</span><br><span class="line"></span><br><span class="line">Any .h, .hh, .hpp or .hxx files will not be compiled separately, but if these header files are changed, the C and C++ files will be recompiled.</span><br></pre></td></tr></table></figure>
 <h2 id="basic-data-type-conversion"><a href="#basic-data-type-conversion" class="headerlink" title="basic data type conversion"></a>basic data type conversion</h2><figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br></pre></td><td class="code"><pre><span class="line">| C                   | Go              |</span><br><span class="line">| ------------------- |:---------------:|</span><br><span class="line">| <span class="keyword">char</span>                | C.<span class="keyword">char</span>          |</span><br><span class="line">| <span class="keyword">signed</span> <span class="keyword">char</span>         | C.schar         |</span><br><span class="line">| <span class="keyword">unsigned</span> <span class="keyword">char</span>       | C.uchar         |</span><br><span class="line">| <span class="keyword">short</span>               | C.<span class="keyword">short</span>         |</span><br><span class="line">| <span class="keyword">unsigned</span> <span class="keyword">short</span>      | C.ushort        |</span><br><span class="line">| <span class="keyword">int</span>                 | C.<span class="keyword">int</span>           |</span><br><span class="line">| <span class="keyword">unsigned</span> <span class="keyword">int</span>        | C.uint          |</span><br><span class="line">| <span class="keyword">long</span>                | C.<span class="keyword">long</span>          |</span><br><span class="line">| <span class="keyword">unsigned</span> <span class="keyword">long</span>       | C.ulong         |</span><br><span class="line">| <span class="keyword">long</span> <span class="keyword">long</span>           | C.longlong      |</span><br><span class="line">| <span class="keyword">unsigned</span> <span class="keyword">long</span> <span class="keyword">long</span>  | C.ulonglong     |</span><br><span class="line">| <span class="keyword">float</span>               | C.<span class="keyword">float</span>         |</span><br><span class="line">| <span class="keyword">double</span>              | C.<span class="keyword">double</span>        |</span><br><span class="line">| <span class="keyword">complex</span> <span class="keyword">float</span>       | C.complexfloat  |</span><br><span class="line">| <span class="keyword">complex</span> <span class="keyword">double</span>      | C.complexdouble |</span><br><span class="line">| <span class="keyword">long</span> <span class="keyword">long</span>           | C.longlong      |</span><br><span class="line">| <span class="keyword">void</span> *              | unsafe.Pointer  |</span><br><span class="line">| <span class="keyword">__int128_t</span>          | [<span class="number">16</span>]byte        |</span><br><span class="line">| <span class="keyword">__uint128_t</span>         | [<span class="number">16</span>]byte        |</span><br><span class="line">| few special C types | uintptr         |</span><br></pre></td></tr></table></figure>
 <figure class="highlight c"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br></pre></td><td class="code"><pre><span class="line">| C                | Go                |</span><br><span class="line">| ---------------- |:-----------------:|</span><br><span class="line">| <span class="keyword">sizeof</span>(T)        | C.sizeof_T        |</span><br><span class="line">| <span class="keyword">sizeof</span>(struct T) | C.sizeof_struct_T |</span><br><span class="line">| <span class="class"><span class="keyword">struct</span> <span class="title">X</span>         | <span class="title">C</span>.<span class="title">struct_X</span>        |</span></span><br><span class="line"><span class="class">| <span class="title">union</span> <span class="title">X</span>          | <span class="title">C</span>.<span class="title">union_X</span>         |</span></span><br><span class="line"><span class="class">| <span class="title">enum</span> <span class="title">X</span>           | <span class="title">C</span>.<span class="title">enum_X</span>          |</span></span><br></pre></td></tr></table></figure>