Question

I’m working on writing my own string class and am having trouble with overloading the += operator for a MyString being +=’d to a char. I figured this would work but with no luck. Here’s the implementation I tried. Any assistance on getting it to work correctly will be much appreciated.

MyString& MyString::operator +=(char c)
{
    char derp[1] = {c};
    strcat(value, derp);
    return *this;
}

Answer 1

This is not going to work for several reasons:

1. derp is not a null-terminated array, which it has to be if you pass it as a parameter to strcat
2. There is no check that the buffer that value represents can actually hold more data; neither is there a facility to make sure that the buffer is always null-terminated (which again it needs to be because you are passing it to strcat)
3. Even if you correct the above, your string class will never be able to include the character \0 as part of a string value because that will be mistaken for a null terminator; in technical terms, your string class would not be “binary safe”; to fix this you need to drop strcat and similar functions entirely and switch to memcpy and friends

Apart from the above, overloading operator += like this allows for code such as

MyString str("foo");
foo += 80; // this compiles, but should it?

Finally, the str*** family of functions is going to get needlessly slower as your strings are getting larger (because they have to scan the string from the beginning each time in order to determine where it ends). Keeping your own length variable and switching to mem*** is going to fix this issue as well.