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| <div class="section" id="cmp0003"> |
| <span id="policy:CMP0003"></span><h1>CMP0003<a class="headerlink" href="#cmp0003" title="Permalink to this headline">ΒΆ</a></h1> |
| <p>Libraries linked via full path no longer produce linker search paths.</p> |
| <p>This policy affects how libraries whose full paths are NOT known are |
| found at link time, but was created due to a change in how CMake deals |
| with libraries whose full paths are known. Consider the code</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>target_link_libraries(myexe /path/to/libA.so) |
| </pre></div> |
| </div> |
| <p>CMake 2.4 and below implemented linking to libraries whose full paths |
| are known by splitting them on the link line into separate components |
| consisting of the linker search path and the library name. The |
| example code might have produced something like</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>... -L/path/to -lA ... |
| </pre></div> |
| </div> |
| <p>in order to link to library A. An analysis was performed to order |
| multiple link directories such that the linker would find library A in |
| the desired location, but there are cases in which this does not work. |
| CMake versions 2.6 and above use the more reliable approach of passing |
| the full path to libraries directly to the linker in most cases. The |
| example code now produces something like</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>... /path/to/libA.so .... |
| </pre></div> |
| </div> |
| <p>Unfortunately this change can break code like</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>target_link_libraries(myexe /path/to/libA.so B) |
| </pre></div> |
| </div> |
| <p>where <code class="docutils literal notranslate"><span class="pre">B</span></code> is meant to find <code class="docutils literal notranslate"><span class="pre">/path/to/libB.so</span></code>. This code is wrong |
| because the user is asking the linker to find library B but has not |
| provided a linker search path (which may be added with the |
| link_directories command). However, with the old linking |
| implementation the code would work accidentally because the linker |
| search path added for library A allowed library B to be found.</p> |
| <p>In order to support projects depending on linker search paths added by |
| linking to libraries with known full paths, the <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior for this |
| policy will add the linker search paths even though they are not |
| needed for their own libraries. When this policy is set to <code class="docutils literal notranslate"><span class="pre">OLD</span></code>, CMake |
| will produce a link line such as</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>... -L/path/to /path/to/libA.so -lB ... |
| </pre></div> |
| </div> |
| <p>which will allow library B to be found as it was previously. When |
| this policy is set to NEW, CMake will produce a link line such as</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>... /path/to/libA.so -lB ... |
| </pre></div> |
| </div> |
| <p>which more accurately matches what the project specified.</p> |
| <p>The setting for this policy used when generating the link line is that |
| in effect when the target is created by an add_executable or |
| add_library command. For the example described above, the code</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>cmake_policy(SET CMP0003 OLD) # or cmake_policy(VERSION 2.4) |
| add_executable(myexe myexe.c) |
| target_link_libraries(myexe /path/to/libA.so B) |
| </pre></div> |
| </div> |
| <p>will work and suppress the warning for this policy. It may also be |
| updated to work with the corrected linking approach:</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>cmake_policy(SET CMP0003 NEW) # or cmake_policy(VERSION 2.6) |
| link_directories(/path/to) # needed to find library B |
| add_executable(myexe myexe.c) |
| target_link_libraries(myexe /path/to/libA.so B) |
| </pre></div> |
| </div> |
| <p>Even better, library B may be specified with a full path:</p> |
| <div class="highlight-none notranslate"><div class="highlight"><pre><span></span>add_executable(myexe myexe.c) |
| target_link_libraries(myexe /path/to/libA.so /path/to/libB.so) |
| </pre></div> |
| </div> |
| <p>When all items on the link line have known paths CMake does not check |
| this policy so it has no effect.</p> |
| <p>Note that the warning for this policy will be issued for at most one |
| target. This avoids flooding users with messages for every target |
| when setting the policy once will probably fix all targets.</p> |
| <p>This policy was introduced in CMake version 2.6.0. CMake version |
| 3.23.1 warns when the policy is not set and uses <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior. Use |
| the <span class="target" id="index-0-command:cmake_policy"></span><a class="reference internal" href="../command/cmake_policy.html#command:cmake_policy" title="cmake_policy"><code class="xref cmake cmake-command docutils literal notranslate"><span class="pre">cmake_policy()</span></code></a> command to set it to <code class="docutils literal notranslate"><span class="pre">OLD</span></code> or <code class="docutils literal notranslate"><span class="pre">NEW</span></code> explicitly.</p> |
| <div class="admonition note"> |
| <p class="admonition-title">Note</p> |
| <p>The <code class="docutils literal notranslate"><span class="pre">OLD</span></code> behavior of a policy is |
| <span class="target" id="index-0-manual:cmake-policies(7)"></span><a class="reference internal" href="../manual/cmake-policies.7.html#manual:cmake-policies(7)" title="cmake-policies(7)"><code class="xref cmake cmake-manual docutils literal notranslate"><span class="pre">deprecated</span> <span class="pre">by</span> <span class="pre">definition</span></code></a> |
| and may be removed in a future version of CMake.</p> |
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