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POremove chars from string in c++
 

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  1. POremove chars from string in c++
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    <p>I was implementing a method to remove certain characters from a string txt, <strong>in-place</strong>. the following is my code. The result is expected as "bdeg". however the result is "bdegfg", which seems the null terminator is not set. the weird thing is that when I use gdb to debug, after setting null terminator </p> <pre><code>(gdb) p txt $5 = (std::string &amp;) @0xbffff248: {static npos = &lt;optimized out&gt;, _M_dataplus = {&lt;std::allocator&lt;char&gt;&gt; = {&lt;__gnu_cxx::new_allocator&lt;char&gt;&gt; = {&lt;No data fields&gt;}, &lt;No data fields&gt;}, _M_p = 0x804b014 "bdeg"}} </code></pre> <p>it looks right to me. So what is the problem here?</p> <pre><code>#include &lt;iostream&gt; #include &lt;string&gt; using namespace std; void censorString(string &amp;txt, string rem) { // create look-up table bool lut[256]={false}; for (int i=0; i&lt;rem.size(); i++) { lut[rem[i]] = true; } int i=0; int j=0; // iterate txt to remove chars for (i=0, j=0; i&lt;txt.size(); i++) { if (!lut[txt[i]]){ txt[j]=txt[i]; j++; } } // set null-terminator txt[j]='\0'; } int main(){ string txt="abcdefg"; censorString(txt, "acf"); // expect: "bdeg" std::cout &lt;&lt; txt &lt;&lt;endl; } </code></pre> <p><strong>follow-up question</strong>:</p> <p>if string is not truncated like c string. so what happens with <code>txt[j]='\0'</code> and why it is "bdegfg" not 'bdeg'\0'g' or some corrupted strings.</p> <p><strong>another follow-up</strong>: if I use <code>txt.erase(txt.begin()+j, txt.end()</code>); it works fine. so I'd better use string related api. the point is that I do not know the time complexity of the underlying code of these api. </p>
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    1. COwhat did you intend this "bool lut[256]={false};" to do? It doesn't initialize the array to all false values.
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      1. USJay
    2. CO@Jay: Actually, it does. So would this: `bool lut[256] = {};` -- When you provide an initializer for an array, any unspecified elements are value initialized. For `bool`, value initialized means `false`.
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      1. USBenjamin Lindley
    3. COI think only by accident though. "The elements of global and static arrays, on the other hand, are automatically initialized with their default values, which for all fundamental types this means they are filled with zeros." i.e. the "={false}" does nothing but initialize the first element to false. All the remaining are the default value, which I would guess is false.
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      1. USJay
 

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