Getting an "L buffer is too small && 0" error from strcpy_s -- trying to make an overloaded + operator

Question

I'm trying to write a simple version of the string class (for practice), and I have everything working except the overloaded + operator.

The line " strcpy_s(temp, strlen(stringPtr) + 1, stringPtr); " keeps throwing an exception. I assume strcat_s will too.

Any advice?

MyString MyString::operator+(const MyString & other)
{
    if (this != &other)
    {

        char * temp = new char[strlen(stringPtr) + strlen(other.stringPtr) + 1];
        strcpy_s(temp, strlen(stringPtr) + 1, stringPtr);
        strcat_s(temp, strlen(other.stringPtr) + 1, other.stringPtr);

        delete[]stringPtr;
        stringPtr = temp;

        delete[]temp;

    }
    return this->stringPtr;
}

If it helps, stringPtr is being passed "bob," and other.stringPtr is being passed "sally."

`stringPtr = temp; delete[] temp;` Now `stringPtr` is garbage (an indeterminate value). Your attempt to use it in `return this->stringPtr` has undefined behavior. — melpomene, Mar 02 '19 at 01:11
@melpomene Thanks! Fixed. Unfortunately it's still giving the error. I put (this != &other) for the edge case of accidentally assigning something to itself. — Lee, Mar 02 '19 at 01:18
@melpomene You're right. I might've gotten my wires crossed there.. — Lee, Mar 02 '19 at 01:20
Don't post it in a comment. Edit your question to include it. — Phil M, Mar 02 '19 at 01:29

Phil M · Answer 1 · 2019-03-02T01:36:28.973

1

You should pass the same size to both functions.

MyString MyString::operator+(const MyString & other)
{
    size_t newSize = strlen(stringPtr) + strlen(other.stringPtr) + 1;
    char * temp = new char[newSize];
    temp[0] = 0;
    strcpy_s(temp, newSize, stringPtr);
    strcat_s(temp, newSize, other.stringPtr);

    //I'm assuming your constructor makes a copy.....    
    MyString ret(temp);
    delete[] temp;
    return ret;
}

You might look at this for more info on a better way to implement some operators. E.g., operator+ is often implemented in terms of operator+=.

edited Mar 02 '19 at 01:36

answered Mar 02 '19 at 01:28

Phil M

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Note, however, that you **know** that the allocated array is large enough for the concatenated strings, so the "secure" checks are redundant. `strcpy` and `strcat` are just as "safe" here. – Pete Becker Mar 02 '19 at 13:36

Getting an "L buffer is too small && 0" error from strcpy_s -- trying to make an overloaded + operator

1 Answers1