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POCompiler error trying to delete template type which is a pointer
 

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  1. POCompiler error trying to delete template type which is a pointer
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    <p>I'm new to C++ and I have the ambition to understand how templates work. So I have implemented a generic list <code>MyList</code> which may contain both built-in primitive types and pointers. In the <code>remove</code> function I want to distinguish pointer types and built-ins so I can delete the object behind the pointer but leave the built-ins untouched. </p> <p>To distinguish the template types, which can be pointers or non-pointers, I wrote the following functions, which work fine:</p> <pre><code>// distinguish between pointer and non-pointer type of template variable template&lt;typename T&gt; bool is_pointer(T t) { return false; } template&lt;typename T&gt; bool is_pointer(T* t) { return true; } </code></pre> <p>In the list function <code>remove</code> the idea was to test for pointers and delete them in case. However, the delete statement does not compile:</p> <pre><code>template&lt;typename T&gt; void MyList&lt;T&gt;::remove() { ... if (is_pointer(temp-&gt;getContent())) { // delete object pointer points to T t = temp-&gt;getContent(); cout &lt;&lt; t; // prints out address // delete t; // produces compiler error (see below) } </code></pre> <p>In the <code>main.cpp</code> I test the list class with various types, I call amongst others:</p> <pre><code>MyList&lt;int&gt; mylist; // with type int mylist.remove(); mylist.add(3); // add and remove elements MyList&lt;string&gt; mylist2; // with type string ... MyList&lt;string*&gt; mylist3; // with type string* mylist.add(new string("three")); mylist.remove(); </code></pre> <p>When I comment out the statement <code>delete t;</code> I can verify that the control flow is correct: the if-statement is only entered for the <code>string*</code> example. However, if I uncomment the <code>delete</code> statement the compiler complains like that:</p> <pre><code>../mylist.h: In member function ‘void MyList&lt;T&gt;::remove() [with T = int]’: ../main.cpp:36:18: instantiated from here ../mylist.h:124:6: error: type ‘int’ argument given to ‘delete’, expected pointer ../mylist.h: In member function ‘void MyList&lt;T&gt;::remove() [with T = std::basic_string&lt;char&gt;]’: ../main.cpp:71:18: instantiated from here ../mylist.h:124:6: error: type ‘struct std::basic_string&lt;char&gt;’ argument given to ‘delete’, expected pointer make: *** [main.o] Error 1 </code></pre> <p>What is it that I don't see? I'm using the <code>delete</code> statement on pointers only but still I get these compiler errors. If I print out <code>t</code> in the if-statement it is a pointer address!</p>
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    1. USThomas789
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    1. CO`T t` is not a pointer, what does `getContent()` return? Also, you are using the `void*` overload for `operator<<` which is why you are seeing the address.
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      1. USJesse Good
    2. COOf course, you can't delete non-pointer types (that have no implicit conversion to an object pointer type). You can use a function `destroy` that has overloads for pointer and non-pointer types just like your `is_pointer`.
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    3. COT t is not a pointer, so you cant delete it
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      1. USshofee
 

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