Qt6 issue with sdrbase/util/baudot.cpp

[gvanem]

While compiling sdrbase/util/baudot.cpp using Qt 6.2.4, I'm getting this compile error from clang-cl (ver 16.0.0):

util/baudot.cpp(182,51): error: use of overloaded operator '==' is ambiguous (with operand types 'QString' and 'char')
    if ((m_characterSet == Baudot::RUSSIAN) && (c == '\0'))
                                                ~ ^  ~~~~
f:\gv\Qt\6.2.4\msvc2019_64\include\QtCore/qstring.h(902,17): note: candidate function
    friend bool operator==(const QString &s1, std::nullptr_t) noexcept { return s1.isEmpty(); }
                ^
f:\gv\Qt\6.2.4\msvc2019_64\include\QtCore/qstring.h(915,17): note: candidate function
    friend bool operator==(const QString &s1, const char16_t *s2) noexcept { return s1 == QStringView(s2); }
                ^
f:\gv\Qt\6.2.4\msvc2019_64\include\QtCore/qstring.h(1356,22): note: candidate function
inline bool QString::operator==(const char *s) const
                     ^
1 error generated.

Similar from cl.

I'm not sure why, but I tried this patch in the hope it's logically similar:

--- a/sdrbase/util/baudot.cpp 2023-03-10 18:07:15
+++ b/sdrbase/util/baudot.cpp 2023-06-12 07:27:35
@@ -165,6 +165,7 @@
 QString BaudotDecoder::decode(char bits)
 {
     QString c = m_figure ? m_figures[(int)bits] : m_letters[(int)bits];
+    QString c_null = "\0";

     if ((c == '>') || (m_unshiftOnSpace && (c == " ")))
     {
@@ -179,7 +180,7 @@
         // Switch to figures
         m_figure = true;
     }
-    if ((m_characterSet == Baudot::RUSSIAN) && (c == '\0'))
+    if ((m_characterSet == Baudot::RUSSIAN) && (c == c_null))
     {
         // Switch to Cyrillic
         m_figure = false;

With this it compiles with both Qt 5 and 6. But I'm not sure what the test should do.

[gvanem]

PS. Same issue in plugins/channelrx/demodrtty/rttydemodsink.cpp:

rttydemodsink.cpp(520,20): error: use of overloaded operator '!=' is ambiguous (with operand types 'QString' and 'char')
            if ((c != '\0') && (c != '<') && (c != '>') && (c != '^'))
                 ~ ^  ~~~~
f:\gv\Qt\6.2.4\msvc2019_64\include\QtCore/qstring.h(903,17): note: candidate function
    friend bool operator!=(const QString &s1, std::nullptr_t) noexcept { return !s1.isEmpty(); }
                ^
f:\gv\Qt\6.2.4\msvc2019_64\include\QtCore/qstring.h(916,17): note: candidate function
    friend bool operator!=(const QString &s1, const char16_t *s2) noexcept { return s1 != QStringView(s2); }
                ^
f:\gv\Qt\6.2.4\msvc2019_64\include\QtCore/qstring.h(1358,22): note: candidate function
inline bool QString::operator!=(const char *s) const
                     ^
1 error generated.

[f4exb]

I can understand the compiler may get confused. If I am not mistaken "c" is just a single character. What happens if we use a QChar instead of a QString?

[srcejon]

c can be a string in some of the more obscure character sets (for representing fractions). Comparing against "\0" is fin

But I would say stick to Qt 5 on Windows, and if you must use 6, don't use Qt 6.2 - use 6.4 (It will be worse than 5 whatever version of 6 you use - for now).