.. title:: clang-tidy - performance-inefficient-string-concatenation

performance-inefficient-string-concatenation
============================================

This check warns about the performance overhead arising from concatenating
strings using the ``operator+``, for instance:

.. code-block:: c++

    std::string a("Foo"), b("Bar");
    a = a + b;

Instead of this structure you should use ``operator+=`` or ``std::string``'s
(``std::basic_string``) class member function ``append()``. For instance:

.. code-block:: c++

   std::string a("Foo"), b("Baz");
   for (int i = 0; i < 20000; ++i) {
       a = a + "Bar" + b;
   }

Could be rewritten in a greatly more efficient way like:

.. code-block:: c++

   std::string a("Foo"), b("Baz");
   for (int i = 0; i < 20000; ++i) {
       a.append("Bar").append(b);
   }

And this can be rewritten too:

.. code-block:: c++

   void f(const std::string&) {}
   std::string a("Foo"), b("Baz");
   void g() {
       f(a + "Bar" + b);
   }

In a slightly more efficient way like:

.. code-block:: c++

   void f(const std::string&) {}
   std::string a("Foo"), b("Baz");
   void g() {
       f(std::string(a).append("Bar").append(b));
   }

Options
-------

.. option:: StrictMode

   When `false`, the check will only check the string usage in ``while``, ``for``
   and ``for-range`` statements. Default is `false`.