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POC++ pointer to new memory storing gibberish
 

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  1. POC++ pointer to new memory storing gibberish
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    <p>I have a class that accepts character arrays. I realize that std::string is preferred for working with strings but this is an excercise to learn about pointers and allocating dynamic memory. The problem I am having is with the overloaded addition operator. I allocate new memory to the size of the two char arrays being concatenated, plus a terminating null character. When I put breakpoints on the for loops I can see the program is iterating through the left hand operand pointer(p) and then the right hand operand pointer(q), but the individual chars are not being stored to temp_str.</p> <p>I am fairly new to C++ so I am sure I am missing something basic about pointers and/or dynamic memory. Any help/advice would be appreciated. Thanks.</p> <pre><code>#include &lt;iostream&gt; #include &lt;cstring&gt; using std::cout; using std::endl; class CStr { private: int m_length; char* m_pstr; public: // Constructor CStr (const char* s = "Default String") { cout &lt;&lt; "Constructor called\n"; m_length = strlen(s) + 1; // Store the length of the string m_pstr = new char[m_length]; // Allocate space for the string strcpy_s(m_pstr,m_length,s); // Copy string to memory } // Copy constructor CStr (const CStr&amp; aStr) { cout &lt;&lt; "Copy constructor called\n"; m_length = aStr.m_length; // Get length of the object to be copied m_pstr = new char [m_length]; // Allocate space for the string strcpy_s(m_pstr, m_length, aStr.m_pstr); // Copy string to memory } // Assignment operator CStr&amp; operator=(const CStr&amp; aStr) { cout &lt;&lt; "Assignment operator called\n"; if(this == &amp;aStr) // Check addresses, if equal return *this; // return the 1st operand m_length = aStr.m_length; // Get length of the rhs operand delete [] m_pstr; // Release memory for the lhs operand m_pstr = new char[m_length]; // Allocate space for the string strcpy_s(m_pstr, m_length, aStr.m_pstr); // Copy rhs operand string to the lhs operand return *this; // Return a reference to the lhs operand } // Addition operator CStr operator+(const CStr&amp; aStr) const { cout &lt;&lt; "Addition operator called\n"; // get the lengths of the strings size_t rhs_length = strlen(aStr.m_pstr); // length of rhs operand size_t lhs_length = strlen(this-&gt;m_pstr); // length of lhs operand char* temp_str = new char[lhs_length + rhs_length + 1]; // Allocate memory to hold concatenated string // plus terminating null character char* p = this-&gt;m_pstr; char* q = aStr.m_pstr; for (p; *p!=0; p++) // Increment lhs string pointer *temp_str++ = *p; // Store character for (q; *q!=0; q++) // Increment rhs string pointer *temp_str++ = *q; // Store character *temp_str++ = '\0'; // Null character at the end return CStr(temp_str); } // Destructor ~CStr () { cout &lt;&lt; Print() &lt;&lt; " has been destroyed\n"; delete [] m_pstr; // Free memory assigned to the pointer } // Print function char* Print() const { return m_pstr; } }; int main() { CStr s1("foo"); CStr s2("bar"); CStr s3 = s1 + s2; } </code></pre>
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    1. USricoflow
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      1. VTUpMod
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    1. COWell to start with, neither your copy-constructor nor your copy-assignment operator sets the `m_length` field.
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      1. USSome programmer dude
    2. COWhy do you have a member, which stores the length of the string, and you don't use it. In all Funktions you call strlen();
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      1. POC++ pointer to new memory storing gibberish
      1. USPatrick Sweigl
    3. COIt would be better style to declare an operator+ as a stand alone binary function.
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      1. POC++ pointer to new memory storing gibberish
      1. USRoss Bencina
 

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