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  <title>Online Demo - Cppcheck</title>
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    <h1><a href="/">Cppcheck</a></h1>
    <p>A tool for static C/C++ code analysis</p>
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<h2>Online Demo</h2>
<form action="/demo/report/" name="f" onsubmit="return checkCodeLength();" method="post" target="_blank">
<p><label for="code">Enter code:</label> <span class="maxChars">(max 1024 characters)</span><br />
<textarea id="code" name="code" rows="20" cols="80">
void f()
{
    char *p;
    *p = 0;
}
</textarea><br />
<input type="submit" value="Check" />
<label><input type="checkbox" name="xml" value="1" />XML output</label></p>
</form>
<h3>Examples</h3>
<p>This code can be copied and pasted in the edit box above.</p>
<h4>NULL pointers</h4>
<pre class="cpp geshicode"><span class="kw4">void</span> f1<span class="br0">(</span><span class="kw4">struct</span> fred_t <span class="sy2">*</span>p<span class="br0">)</span>
<span class="br0">{</span>
    <span class="co1">// dereference p and then check if it's NULL</span>
    <span class="kw4">int</span> x <span class="sy1">=</span> p<span class="sy2">-</span><span class="sy1">&gt;</span>x<span class="sy4">;</span>
    <span class="kw1">if</span> <span class="br0">(</span>p<span class="br0">)</span>
        do_something<span class="br0">(</span>x<span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>

<span class="kw4">void</span> f2<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">const</span> <span class="kw4">char</span> <span class="sy2">*</span>p <span class="sy1">=</span> <span class="kw2">NULL</span><span class="sy4">;</span>
    <span class="kw1">for</span> <span class="br0">(</span><span class="kw4">int</span> i <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span> str<span class="br0">[</span>i<span class="br0">]</span> <span class="sy3">!</span><span class="sy1">=</span> <span class="st0">'<span class="es5">\0</span>'</span><span class="sy4">;</span> i<span class="sy2">++</span><span class="br0">)</span>
    <span class="br0">{</span>
        <span class="kw1">if</span> <span class="br0">(</span>str<span class="br0">[</span>i<span class="br0">]</span> <span class="sy1">==</span> <span class="st0">' '</span><span class="br0">)</span>
        <span class="br0">{</span>
            p <span class="sy1">=</span> str <span class="sy2">+</span> i<span class="sy4">;</span>
            <span class="kw1">break</span><span class="sy4">;</span>
        <span class="br0">}</span>
    <span class="br0">}</span>

    <span class="co1">// p is NULL if str doesn't have a space. If str always has a</span>
    <span class="co1">// a space then the condition (str[i] != '\0') would be redundant</span>
    <span class="kw1">return</span> p<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span><span class="sy4">;</span>
<span class="br0">}</span>

<span class="kw4">void</span> f3<span class="br0">(</span><span class="kw4">int</span> a<span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">struct</span> fred_t <span class="sy2">*</span>p <span class="sy1">=</span> <span class="kw2">NULL</span><span class="sy4">;</span>
    <span class="kw1">if</span> <span class="br0">(</span>a <span class="sy1">==</span> <span class="nu0">1</span><span class="br0">)</span>
        p <span class="sy1">=</span> fred1<span class="sy4">;</span>

    <span class="co1">// if a is not 1 then p is NULL</span>
    p<span class="sy2">-</span><span class="sy1">&gt;</span>x <span class="sy1">=</span> <span class="nu0">0</span><span class="sy4">;</span>
<span class="br0">}</span></pre>
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