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Asked: 2026-05-10T20:01:09+00:00

I’m trying to write a wstring to file with ofstream in binary mode, but

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I’m trying to write a wstring to file with ofstream in binary mode, but I think I’m doing something wrong. This is what I’ve tried:

ofstream outFile('test.txt', std::ios::out | std::ios::binary); wstring hello = L'hello'; outFile.write((char *) hello.c_str(), hello.length() * sizeof(wchar_t)); outFile.close();

Opening test.txt in for example Firefox with encoding set to UTF16 it will show as:

h�e�l�l�o�

Could anyone tell me why this happens?

EDIT:

Opening the file in a hex editor I get:

FF FE 68 00 00 00 65 00 00 00 6C 00 00 00 6C 00 00 00 6F 00 00 00

Looks like I get two extra bytes in between every character for some reason?

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1 Answer

  1. I suspect that sizeof(wchar_t) is 4 in your environment – i.e. it’s writing out UTF-32/UCS-4 instead of UTF-16. That’s certainly what the hex dump looks like.

    That’s easy enough to test (just print out sizeof(wchar_t)) but I’m pretty sure it’s what’s going on.

    To go from a UTF-32 wstring to UTF-16 you’ll need to apply a proper encoding, as surrogate pairs come into play.

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