stl string append函数

basic_string<_CharT,_Traits,_Alloc>::append(size_type __n, _CharT __c) {

if (__n > max_size() || size() > max_size() - __n)

_M_throw_length_error();

if (size() + __n > capacity())

reserve(size() + max(size(), __n));

if (__n > 0) {

uninitialized_fill_n(_M_finish + 1, __n - 1, __c);

__STL_TRY {

_M_construct_null(_M_finish + __n);

}

__STL_UNWIND(destroy(_M_finish + 1, _M_finish + __n));

_Traits::assign(*_M_finish, __c);

_M_finish += __n;

}

return *this;

}