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POcrash, delete [ ] this->str
 

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    <p>Hello I've got some <strong>troubles to delete a member string</strong> of my class which is isn't null and which points to the right location since <strong>I can display my string "hello world" just before.</strong></p> <p>I call the function mystringclass::alloc() from another member function afterwards this->str was supposed to get another string content larger.</p> <p><strong>The process worked fine a first time when I resized the same way "hello" to get "hello world".</strong> But now I want to enlarge it again it doesn't. So I'm confused.</p> <p>Please help me.</p> <pre><code>void mystringclass::alloc(long newsize) //newsize includes the +1 char { cout &lt;&lt; "old size was: " &lt;&lt; this-&gt;size &lt;&lt; endl; //displays "12" if(this-&gt;str) cout &lt;&lt; this-&gt;str &lt;&lt; endl; //displays "hello world" all is right till here if(this-&gt;str) delete [] this-&gt;str ; //it crashes here cout &lt;&lt; "str deleted\n"; //never show up on screen this-&gt;str = new char[newsize + 1]; this-&gt;size = newsize; this-&gt;str[0] = 0; } </code></pre> <hr> <p>Thanks for your answers, I tried to clear my code to post it here. My bug disappeared but another one came up and having something to do with the rule of three:</p> <pre><code>int main() { stringclass str = "Hello"; stringclass str2 = str; return 0; } </code></pre> <p>I display info all along procedures <strong>So the problem is that str2 is already equal to "hello" even before affecting the content of str in my copy constructor. And is empty after the copy.</strong> What's wrong? As some may say, I learned c++ in a magicbox. I'm using codeblocks 10.05</p> <p><strong>Full code :</strong></p> <pre><code>#include &lt;fstream&gt; #include &lt;iostream&gt; #include &lt;vector&gt; using namespace std; class stringclass { protected : inline bool success() { failbit = false; return true; } inline bool fail() { failbit = true; return false; } public : bool failbit; char * mystring; long memsize; long length; void alloc(long newsize); void reset(); void copy(const stringclass &amp; other); stringclass() {reset(); } stringclass(const stringclass &amp; other) {copy(other); } stringclass(const char str[]); ~stringclass() {delete [] mystring;} inline long get_length() { if(mystring) length = strlen(mystring); return length;} inline long get_memsize() const { return memsize; } friend ostream&amp; operator &lt;&lt; (ostream&amp; out, stringclass &amp; sc){out &lt;&lt; sc.mystring; return out;} stringclass &amp; operator = (stringclass &amp; other) { copy(other); return *this;} }; void stringclass::reset() { delete [] mystring; mystring = NULL; length = 0; memsize = 0; } void stringclass::alloc(long newsize) { cout&lt;&lt; "\nalloc(long newsize)... \n" &lt;&lt; endl; cout &lt;&lt; "memsize was : " &lt;&lt; memsize &lt;&lt; endl; cout &lt;&lt; "length was : " &lt;&lt; length &lt;&lt; endl; if(mystring) cout &lt;&lt; "mystring = " &lt;&lt; mystring &lt;&lt; endl; delete [] mystring; cout &lt;&lt; "mystring deleted...\n"; mystring = new char[newsize]; cout &lt;&lt; "mystring has been resized\n"; mystring[0] = 0; memsize = newsize; length = strlen(mystring); cout &lt;&lt; "memsize is now : " &lt;&lt; memsize &lt;&lt; endl; cout &lt;&lt; "length is now : " &lt;&lt; length &lt;&lt; endl; cout&lt;&lt; "\nend of alloc()... " &lt;&lt; endl; cout &lt;&lt; "\n"; } void stringclass::copy(const stringclass &amp; other) { cout &lt;&lt; "\n"; cout &lt;&lt; "copy(const stringclass &amp; other)...\n" &lt;&lt; endl; cout &lt;&lt; "other.mystring = "&lt;&lt; other.mystring &lt;&lt; endl; if(other.mystring == NULL || other.memsize == 0) { reset(); return; } alloc(other.memsize); strcpy(mystring, other.mystring); cout &lt;&lt; "mystring = "&lt;&lt; mystring; length = strlen(mystring); cout &lt;&lt; "length: " &lt;&lt; length &lt;&lt; endl; cout&lt;&lt; "\nend of copy()... " &lt;&lt; endl; cout &lt;&lt; "\n"; } stringclass::stringclass(const char str[]) : mystring(NULL), memsize(0), length(0) { if(str == NULL) reset(); else { alloc(strlen(str) + 1); strcpy(mystring, str); length = strlen(mystring); } } int main() { stringclass str = "Hello"; stringclass str2 = str; cout &lt;&lt; "\nback to main()...\n"; cout &lt;&lt; "str = " &lt;&lt; str &lt;&lt; "\n"; cout &lt;&lt; "str2 = " &lt;&lt; str2 &lt;&lt; "\n"; cout &lt;&lt; endl; system("PAUSE"); return 0; } </code></pre> <p><strong>Result on screen :</strong></p> <pre><code>alloc(long newsize)... memsize was : 0 length was : 0 mystring deleted... mystring has been resized memsize is now : 6 length is now : 0 end of alloc()... copy(const stringclass &amp; other)... other.mystring = Hello alloc(long newsize)... memsize was : 3214960 length was : 2293560 mystring = Hello mystring deleted... mystring has been resized memsize is now : 6 length is now : 0 end of alloc()... mystring = length: 0 end of copy()... back to main()... str = str2 = Appuyez sur une touche pour continuer... </code></pre> <p>I've just realized that the following code isn't necessary for you :</p> <pre><code> protected : inline bool success() { failbit = false; return true; } inline bool fail() { failbit = true; return false; } public : bool failbit; </code></pre> <p>So <strong>I put off these two functions and this variable</strong>, and guess what.. all worked fine, <strong>no bug</strong>. They are not even used once. <strong>I put it back and the problem came back</strong> as well. How could you explain that?! I'm already losing my hairs.</p>
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    1. COIt doesn't matter if it's a null pointer. Deleting a null pointer is a no-op.
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    2. COIt's difficult to say what's wrong, there's not enough information here. Construct a [complete minimal test-case](http://sscce.org).
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    3. COSince `str` is clearly a dynamic pointer, I don't suppose you're abiding by the [Rule of Three](http://en.wikipedia.org/wiki/Rule_of_three_(C%2B%2B_programming)) in your `mystringclass` copy constructor and assignment operator overrides (or perhaps you don't have either/both??)
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