Description
Hello, I'm trying to understand what write_to_string expected to do. For example, for rosidl_runtime_c__U16String with content "Hello World", I expect that resulted std::string will also have contents "Hello World". But because write_to_string bruteforce fully copies underlay memory, I see that after every char there is a null byte (which is treated as string terminate character).
When I try to print such string I get smth like
H
e
l
l
o
W
o
r
l
d
String conversion between std::string and std::wstring is quite complex topic, coversion may not succeed (narrowing conversion from char16 to char8). I'm not generally sure that what you do here is right, because as a result you get ill-formed string.
Should instead smth like std::codecvt_utf8_utf16 be used or wstring considered unsupported by rosidl_typesupport_protobuf?
More details
underlay memory
48 0 65 0 6c 0 6c 0 6f 0 20 0 57 0 6f 0 72 0 6c 0 64 0 <-- initial rosidl_runtime_c__U16String
48 0 65 0 6c 0 6c 0 6f 0 20 0 57 0 6f 0 72 0 6c 0 64 0 <-- converted std::string
48 65 6c 6c 6f 20 57 6f 72 6c 64 <-- expected std::string
following code was used to print above
void print_memory( const void * mem, unsigned int n ) {
const char * p = reinterpret_cast< const char *>( mem );
for ( unsigned int i = 0; i < n; i++ ) {
std::cout << std::hex << int(p[i]) << " ";
} std::cout << std::endl;
}
TEST(test_wstring_conversion, write_to_string) {
rosidl_runtime_c__U16String wstr;
ASSERT_TRUE(rosidl_runtime_c__U16String__init(&wstr));
ASSERT_TRUE(rosidl_runtime_c__U16String__assign(&wstr, reinterpret_cast<const uint16_t*>(u"Hello World")));
std::string converted_str;
rosidl_typesupport_protobuf_c::write_to_string(wstr, converted_str);
std::string expected_str{"Hello World"};
print_memory(wstr.data, wstr.size * (sizeof(uint16_t) / sizeof(char)));
print_memory(converted_str.data(), converted_str.size());
print_memory(expected_str.data(), expected_str.size());
}