summaryrefslogtreecommitdiff
path: root/absl/strings/internal/ostringstream.h
diff options
context:
space:
mode:
Diffstat (limited to 'absl/strings/internal/ostringstream.h')
-rw-r--r--absl/strings/internal/ostringstream.h97
1 files changed, 97 insertions, 0 deletions
diff --git a/absl/strings/internal/ostringstream.h b/absl/strings/internal/ostringstream.h
new file mode 100644
index 00000000..017632a9
--- /dev/null
+++ b/absl/strings/internal/ostringstream.h
@@ -0,0 +1,97 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
+#define ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_
+
+#include <cassert>
+#include <ostream>
+#include <streambuf>
+#include <string>
+
+#include "absl/base/port.h"
+
+namespace absl {
+namespace strings_internal {
+
+// The same as std::ostringstream but appends to a user-specified std::string,
+// and is faster. It is ~70% faster to create, ~50% faster to write to, and
+// completely free to extract the result std::string.
+//
+// std::string s;
+// OStringStream strm(&s);
+// strm << 42 << ' ' << 3.14; // appends to `s`
+//
+// The stream object doesn't have to be named. Starting from C++11 operator<<
+// works with rvalues of std::ostream.
+//
+// std::string s;
+// OStringStream(&s) << 42 << ' ' << 3.14; // appends to `s`
+//
+// OStringStream is faster to create than std::ostringstream but it's still
+// relatively slow. Avoid creating multiple streams where a single stream will
+// do.
+//
+// Creates unnecessary instances of OStringStream: slow.
+//
+// std::string s;
+// OStringStream(&s) << 42;
+// OStringStream(&s) << ' ';
+// OStringStream(&s) << 3.14;
+//
+// Creates a single instance of OStringStream and reuses it: fast.
+//
+// std::string s;
+// OStringStream strm(&s);
+// strm << 42;
+// strm << ' ';
+// strm << 3.14;
+//
+// Note: flush() has no effect. No reason to call it.
+class OStringStream : private std::basic_streambuf<char>, public std::ostream {
+ public:
+ // The argument can be null, in which case you'll need to call str(p) with a
+ // non-null argument before you can write to the stream.
+ //
+ // The destructor of OStringStream doesn't use the std::string. It's OK to destroy
+ // the std::string before the stream.
+ explicit OStringStream(std::string* s) : std::ostream(this), s_(s) {}
+
+ std::string* str() { return s_; }
+ const std::string* str() const { return s_; }
+ void str(std::string* s) { s_ = s; }
+
+ private:
+ using Buf = std::basic_streambuf<char>;
+
+ Buf::int_type overflow(int c = Buf::traits_type::eof()) override {
+ assert(s_);
+ if (!Buf::traits_type::eq_int_type(c, Buf::traits_type::eof()))
+ s_->push_back(static_cast<char>(c));
+ return 1;
+ }
+
+ std::streamsize xsputn(const char* s, std::streamsize n) override {
+ assert(s_);
+ s_->append(s, n);
+ return n;
+ }
+
+ std::string* s_;
+};
+
+} // namespace strings_internal
+} // namespace absl
+
+#endif // ABSL_STRINGS_INTERNAL_OSTRINGSTREAM_H_