Question

I have the simplest class text:

class Text
{
    char* txt;
public:
    Text(const char*);
    Text(const Text&);
    ~Text();

    const Text operator+(const Text&) const;
};

and implementation:

#include "text.h"

Text::~Text()
{
    delete[] this->txt;
}


Text::Text(const char* argText)
{
    txt = new char[strlen(argText)+1];
    strcpy(txt, argText);
}

Text::Text(const Text& other)
{
    txt = new char[strlen(other.txt)+1];
    strcpy(txt, other.txt);
}

const Text Text::operator+(const Text& other) const
{
    char* ttxt, *newLine;
    ttxt = new char[strlen(txt)+strlen(other.txt)+2];
    strcat(ttxt, this->txt);
    newLine = new char[2];
    newLine[0] = '\n';
    newLine[1] = '\0';
    strcat(ttxt, newLine);
    strcat(ttxt, other.txt);
    Text temp(ttxt);
    delete[] newLine;
    return temp;
}

and main:

#include "text.h"

int main()
{
    Text a("First text.");
    Text b("Second lol!!\n kthxbye!!!!!!!");
    Text c(a+b);
}

and the program breaks on newLine = new char[2]; I tried increasing it, like new char[5] but still it breaks. The message I recieve is:

Windows has triggered a breakpoint in prTextClass.exe.

This may be due to a corruption of the heap, which indicates a bug in
prTextClass.exe or any of the DLLs it has loaded…

Answer 1

const Text Text::operator+(const Text& other) const
{
    char* ttxt, *newLine;
    ttxt = new char[strlen(txt)+strlen(other.txt)+2];
    strcat(ttxt, this->txt);
 // ^^^^^^^^^^^^^^^^^^^^^^^^ This line is buggy
    newLine = new char[2];
    newLine[0] = '\n';
    newLine[1] = '\0';
    strcat(ttxt, newLine);
    strcat(ttxt, other.txt);
    Text temp(ttxt);
    // ....

Note that ttxt = new char[strlen(txt)+strlen(other.txt)+2]; does not initialize the array content. Thus, when strcat() is called, it goes through ttxt to find the first '\0' character as the end of string ttxt and thus stopped at an unknown position.

You should change it into

strcpy(ttxt, this->txt);