2 ms·

Reserve sets the capacity, not the size. If you were to reserve and overwrite the buffer, the size is still wrong. Now if you resize, STL overwrites your conten

• spacechild1 3y ago
  Of course, you need to call push_back() or insert() to add the data. Actually, insert() wouldn't even require reserve() in the first place. I guess the idea of uninitialized resize is that you reserve the space, bump the size, and then you can directly set the new members with operator[]. If your input data is not contiguous, and would need to use push_back() otherwise, you can save a few if-checks. But that's pretty much it, I assume.
• gary_0 3y ago
  Also I don't think the Standard requires that data() returns a valid pointer after only calling reserve(), so it's technically UB.
  • zabzonk 3y ago
    i think you may have misunderstood the standard - data() will always return a valid pointer, but the pointer returned may be invalidated by any number of functions: string s; s.reserve(50); char * p = s.data(); // ok so far s.reserve(100); // now p may be invalid