Question

I get an access violation error when I use a self written Buffer class:

template<typename T> 
class Buffer {
public:
    Buffer(T *data, size_t len);
    Buffer(size_t len);

    size_t len();

    operator T*();
    T& operator[] (const int x) const {
        return this->data[x];
    };

private:
    T *data;
    size_t _len;
};

int main() {
    Buffer<char> b("123", 3);
    b[0] = 0; // This line causes "Access violation writing location 0x003c8830".

    return 0;
}

Why is that? What am I doing wrong?

Answer 1

The code that causes the issue is not in the post, but it’s very likely your constructor: if you assign the pointer data to the member data, then you store the string constant inside your class. Then code of the main than tries to write into non-writable memory, causing access violation.

You can fix your constructor to avoid this problem:

Buffer(T *dataIn, size_t len) {
    data = new T[len];
    memcpy(data, dataIn, len*sizeof(T));
}