diff options
Diffstat (limited to 'src/google/protobuf/io/zero_copy_stream_impl_lite.h')
| -rw-r--r-- | src/google/protobuf/io/zero_copy_stream_impl_lite.h | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/src/google/protobuf/io/zero_copy_stream_impl_lite.h b/src/google/protobuf/io/zero_copy_stream_impl_lite.h index e18da72c..a517161d 100644 --- a/src/google/protobuf/io/zero_copy_stream_impl_lite.h +++ b/src/google/protobuf/io/zero_copy_stream_impl_lite.h @@ -334,6 +334,18 @@ class LIBPROTOBUF_EXPORT CopyingOutputStreamAdaptor : public ZeroCopyOutputStrea // =================================================================== +// mutable_string_data() and as_string_data() are workarounds to improve +// the performance of writing new data to an existing string. Unfortunately +// the methods provided by the string class are suboptimal, and using memcpy() +// is mildly annoying because it requires its pointer args to be non-NULL even +// if we ask it to copy 0 bytes. Furthermore, string_as_array() has the +// property that it always returns NULL if its arg is the empty string, exactly +// what we want to avoid if we're using it in conjunction with memcpy()! +// With C++11, the desired memcpy() boils down to memcpy(..., &(*s)[0], size), +// where s is a string*. Without C++11, &(*s)[0] is not guaranteed to be safe, +// so we use string_as_array(), and live with the extra logic that tests whether +// *s is empty. + // Return a pointer to mutable characters underlying the given string. The // return value is valid until the next time the string is resized. We // trust the caller to treat the return value as an array of length s->size(). @@ -347,6 +359,19 @@ inline char* mutable_string_data(string* s) { #endif } +// as_string_data(s) is equivalent to +// ({ char* p = mutable_string_data(s); make_pair(p, p != NULL); }) +// Sometimes it's faster: in some scenarios p cannot be NULL, and then the +// code can avoid that check. +inline std::pair<char*, bool> as_string_data(string* s) { + char *p = mutable_string_data(s); +#ifdef LANG_CXX11 + return make_pair(p, true); +#else + return make_pair(p, p != NULL); +#endif +} + } // namespace io } // namespace protobuf |