why is delete being called in stdc++ library when there is no delete nor free in the code flow?

Question

I am having a problem debugging my code and am a bit confused by the gdb output. I have attached the gdb output below. The last 2 lines, line #13 and #14 are my code, but everything else is from the C++ library. What is confusing to me is that from about line #7 upward, it appears to be calling delete. This is initialization code and there are no deletes nor frees being called in the code flow. But something is causing delete to be called somewhere in the C++ library. this is on a debian box with g++ 4.7.2 Anybody have a clue that could help me along? EDIT: thanks you guys for your help. I indeed think there is something else going on here. Since the intent of my code is to construct a string using several append() calls, I added a call to reserve() in the ctor for that string so it would be large enough to handle a few append() calls without having to get more space. This has apparently helped because it is now harder for me to force the crash. But I do agree that the cause is probab…

Accepted Answer

You are calling `std::string::append`, that ultimately results in `delete` getting called. If we go through the steps involved in `std::string::append`, it might make more sense why `delete` gets called.

Say you have:

```
std::string s("abc");
s.append("def");
```

When you create `s`, memory has to be allocated to hold `"abc"`. At the end of `s.append("def");`, there has to be enough memory associated with `s` to hold `"abcdef"`. Steps to get there:

- Get the length of `s` => `3`.

- Get the length of the input string `"def"` => `3`.

- Add them to figure out the length of the new string. => `6`.

- Allocate memory to hold the new string.

- Copy `"abc"` to the newly allocated memory.

- Append `"def"` to the newly allocated memory.

- Associate the newly allocated memory with `s`.

- Delete the old memory associated with `s`. (This is where `delete` comes into picture).

why is delete being called in stdc++ library when there is no delete nor free in the code flow?

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