add string resize

iguana/detail/string_resize.hpp

@@ -0,0 +1,131 @@
+#pragma once
+#include <cstddef>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace iguana::detail {
+
+#if __cpp_lib_string_resize_and_overwrite >= 202110L
+template <typename ch>
+inline void resize(std::basic_string<ch> &str, std::size_t sz) {
+  str.resize_and_overwrite(sz, [sz](ch *, std::size_t) {
+    return sz;
+  });
+}
+#elif (defined(_MSC_VER) && _MSC_VER <= 1920)
+// old msvc don't support visit private, discard it.
+
+#else
+
+template <typename Function, Function func_ptr>
+class string_thief {
+ public:
+  friend void string_set_length_hacker(std::string &self, std::size_t sz) {
+#if defined(_MSVC_STL_VERSION)
+    (self.*func_ptr)._Myval2._Mysize = sz;
+#else
+#if defined(_LIBCPP_VERSION)
+    (self.*func_ptr)(sz);
+#else
+#if (_GLIBCXX_USE_CXX11_ABI == 0) && defined(__GLIBCXX__)
+    (self.*func_ptr)()->_M_set_length_and_sharable(sz);
+#else
+#if defined(__GLIBCXX__)
+    (self.*func_ptr)(sz);
+#endif
+#endif
+#endif
+#endif
+  }
+};
+
+#if defined(__GLIBCXX__)  // libstdc++
+#if (_GLIBCXX_USE_CXX11_ABI == 0)
+template class string_thief<decltype(&std::string::_M_rep),
+                            &std::string::_M_rep>;
+#else
+template class string_thief<decltype(&std::string::_M_set_length),
+                            &std::string::_M_set_length>;
+#endif
+#elif defined(_LIBCPP_VERSION)
+template class string_thief<decltype(&std::string::__set_size),
+                            &std::string::__set_size>;
+#elif defined(_MSVC_STL_VERSION)
+template class string_thief<decltype(&std::string::_Mypair),
+                            &std::string::_Mypair>;
+#endif
+
+void string_set_length_hacker(std::string &, std::size_t);
+
+template <typename ch>
+inline void resize(std::basic_string<ch> &raw_str, std::size_t sz) {
+  std::string &str = *reinterpret_cast<std::string *>(&raw_str);
+#if defined(__GLIBCXX__) || defined(_LIBCPP_VERSION) || \
+    defined(_MSVC_STL_VERSION)
+  if (sz > str.capacity()) {
+    str.reserve(sz);
+  }
+  string_set_length_hacker(str, sz);
+  str[sz] = '\0';
+#else
+  raw_str.resize(sz);
+#endif
+}
+
+#endif
+
+#if (defined(_MSC_VER) && _MSC_VER <= 1920)
+#else
+void vector_set_length_hacker(std::vector<char> &self, std::size_t sz);
+
+template <typename Function, Function func_ptr>
+class vector_thief {
+ public:
+  friend void vector_set_length_hacker(std::vector<char> &self,
+                                       std::size_t sz) {
+#if defined(_MSVC_STL_VERSION)
+    (self.*func_ptr)._Myval2._Mylast = self.data() + sz;
+#else
+#if defined(_LIBCPP_VERSION)
+#if _LIBCPP_VERSION < 14000
+    ((*(std::__vector_base<char, std::allocator<char> > *)(&self)).*func_ptr) =
+        self.data() + sz;
+#else
+    (self.*func_ptr) = self.data() + sz;
+#endif
+#else
+#if defined(__GLIBCXX__)
+    ((*(std::_Vector_base<char, std::allocator<char> > *)(&self)).*func_ptr)
+        ._M_finish = self.data() + sz;
+#endif
+#endif
+#endif
+  }
+};
+
+#if defined(__GLIBCXX__)  // libstdc++
+template class vector_thief<decltype(&std::vector<char>::_M_impl),
+                            &std::vector<char>::_M_impl>;
+#elif defined(_LIBCPP_VERSION)
+template class vector_thief<decltype(&std::vector<char>::__end_),
+                            &std::vector<char>::__end_>;
+#elif defined(_MSVC_STL_VERSION)
+template class vector_thief<decltype(&std::vector<char>::_Mypair),
+                            &std::vector<char>::_Mypair>;
+#endif
+
+template <typename ch>
+inline void resize(std::vector<ch> &raw_vec, std::size_t sz) {
+#if defined(__GLIBCXX__) ||                                       \
+    (defined(_LIBCPP_VERSION) && defined(_LIBCPP_HAS_NO_ASAN)) || \
+    defined(_MSVC_STL_VERSION)
+  std::vector<char> &vec = *reinterpret_cast<std::vector<char> *>(&raw_vec);
+  vec.reserve(sz);
+  vector_set_length_hacker(vec, sz);
+#else
+  raw_vec.resize(sz);
+#endif
+}
+#endif
+};  // namespace iguana::detail

iguana/pb_writer.hpp

@@ -1,5 +1,6 @@
 #pragma once
 #include "pb_util.hpp"
+#include "detail/string_resize.hpp"
 
 namespace iguana {
 namespace detail {