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debugging.html
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<a class="link" href="appendix-i-keywords.html">Appendix I: Keywords</a>
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<a class="link" href="appendix-ii-operators.html">Appendix II: Operators</a>
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<h1 class="main">Debugging</h1>
<h2 id="c-backend-binaries-(default)">C Backend binaries (Default) <a href="debugging.html#c-backend-binaries-(default)" class="header-anchor" aria-hidden="true">#</a></h2>
<p>To debug issues in the generated binary (flag: <code>-b c</code>), you can pass these flags:</p>
<ul>
<li><code>-g</code> - produces a less optimized executable with more debug information in it.
V will enforce line numbers from the .v files in the stacktraces, that the
executable will produce on panic. It is usually better to pass -g, unless
you are writing low level code, in which case use the next option <code>-cg</code>.</li>
<li><code>-cg</code> - produces a less optimized executable with more debug information in it.
The executable will use C source line numbers in this case. It is frequently
used in combination with <code>-keepc</code>, so that you can inspect the generated
C program in case of panic, or so that your debugger (<code>gdb</code>, <code>lldb</code> etc.)
can show you the generated C source code.</li>
<li><code>-showcc</code> - prints the C command that is used to build the program.</li>
<li><code>-show-c-output</code> - prints the output, that your C compiler produced
while compiling your program.</li>
<li><code>-keepc</code> - do not delete the generated C source code file after a successful
compilation. Also keep using the same file path, so it is more stable,
and easier to keep opened in an editor/IDE.</li>
</ul>
<p>For best debugging experience if you are writing a low level wrapper for an existing
C library, you can pass several of these flags at the same time:
<code>v -keepc -cg -showcc yourprogram.v</code>, then just run your debugger (gdb/lldb) or IDE
on the produced executable <code>yourprogram</code>.</p>
<p>If you just want to inspect the generated C code,
without further compilation, you can also use the <code>-o</code> flag (e.g. <code>-o file.c</code>).
This will make V produce the <code>file.c</code> then stop.</p>
<p>If you want to see the generated C source code for <em>just</em> a single C function,
for example <code>main</code>, you can use: <code>-printfn main -o file.c</code>.</p>
<p>To debug the V executable itself you need to compile from src with <code>./v -g -o v cmd/v</code>.</p>
<p>You can debug tests with for example <code>v -g -keepc prog_test.v</code>. The <code>-keepc</code> flag is needed,
so that the executable is not deleted, after it was created and ran.</p>
<p>To see a detailed list of all flags that V supports,
use <code>v help</code>, <code>v help build</code> and <code>v help build-c</code>.</p>
<p><strong>Commandline Debugging</strong></p>
<ol>
<li>compile your binary with debugging info <code>v -g hello.v</code></li>
<li>debug with <a href="https://lldb.llvm.org">lldb</a> or <a href="https://www.gnu.org/software/gdb/">GDB</a>
e.g. <code>lldb hello</code></li>
</ol>
<p><a href="https://github.com/vlang/v/wiki/Troubleshooting-(debugging)-executables-created-with-V-in-GDB">Troubleshooting (debugging) executables created with V in GDB</a></p>
<p><strong>Visual debugging Setup:</strong></p>
<ul>
<li><a href="https://github.com/vlang/v/blob/master/doc/vscode.md">Visual Studio Code</a></li>
</ul>
<h2 id="native-backend-binaries">Native Backend binaries <a href="debugging.html#native-backend-binaries" class="header-anchor" aria-hidden="true">#</a></h2>
<p>Currently there is no debugging support for binaries, created by the
native backend (flag: <code>-b native</code>).</p>
<h2 id="javascript-backend">Javascript Backend <a href="debugging.html#javascript-backend" class="header-anchor" aria-hidden="true">#</a></h2>
<p>To debug the generated Javascript output you can activate source maps:
<code>v -b js -sourcemap hello.v -o hello.js</code></p>
<p>For all supported options check the latest help:
<code>v help build-js</code></p>
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