Question

I was reviewing my skills with pointers and buffer in C++. I tried the code below and everything works fine. No leaks, no crash, nothing.

To be honest I didn’t expect this.

When I call char* buf2 = new char[strlen(buf)] I didn’t expect srlen(buf) returning the right size. I always thought that strlen
needs a NULL terminated string to work. Here it is not the case so why it is working this code?

        int main(){
             const char* mystr = "mineminemine";
             char* buf = new char[strlen(mystr)];
             memcpy(buf, mystr, strlen(mystr));

             char* buf2 = new char[strlen(buf)];
             memcpy(buf2, buf, strlen(buf));

             delete[] buf2;
             delete[] buf;
        }

Answer 1

That’s called undefined behavior – the program appears working but you can’t rely on that.

When memory is allocated there happens a null character somewhere that is close enough to the start of the buffer and the program can technically access all memory between that null character and the start of the buffer so you don’t observe a crash.

You can’t rely on that behavior. Don’t write code like that, always allocate enough space to store the terminating null character.