Introduce qUtf8Printable() macro to qglobal.h

This macro is equivalent to arg.toUtf8().constData().
It is usable for "%s" arguments of qDebug(), qWarning(), qFatal(),
qCritical().

Change-Id: I2d9956e6651271e1e2183dce9c835511cf923bf3
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 27 insertions, 9 deletions

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index fb95a1966f..98460481ca 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -580,8 +580,8 @@ Q_STATIC_ASSERT_X(UCHAR_MAX == 255, "Qt assumes that char is 8 bits");
     64-bit integer literals in a platform-independent way. The
     Q_CHECK_PTR() macro prints a warning containing the source code's
     file name and line number, saying that the program ran out of
-    memory, if the pointer is 0. The qPrintable() macro represent an
-    easy way of printing text.
+    memory, if the pointer is 0. The qPrintable() and qUtf8Printable()
+    macros represent an easy way of printing text.
 
     Finally, the QT_POINTER_SIZE macro expands to the size of a
     pointer in bytes, and the QT_VERSION and QT_VERSION_STR macros
@@ -3356,17 +3356,31 @@ int qrand()
     qPrintable() is used. This is because the array returned by
     QString::toLocal8Bit() will fall out of scope.
 
+    \note qDebug(), qWarning(), qCritical(), qFatal() expect %s
+    arguments to be UTF-8 encoded, while qPrintable() converts to
+    local 8-bit encoding. Therefore qUtf8Printable() should be used
+    for logging strings instead of qPrintable().
+
+    \sa qUtf8Printable()
+*/
+
+/*!
+    \macro const char *qUtf8Printable(const QString &str)
+    \relates <QtGlobal>
+    \since 5.4
+
+    Returns \a str as a \c{const char *}. This is equivalent to
+    \a{str}.toUtf8().constData().
+
+    The char pointer will be invalid after the statement in which
+    qUtf8Printable() is used. This is because the array returned by
+    QString::toUtf8() will fall out of scope.
+
     Example:
 
     \snippet code/src_corelib_global_qglobal.cpp 37
 
-    \note qDebug(), qWarning(), qCritical(), qFatal() expect %s
-    arguments to be UTF-8 encoded, while qPrintable() converts to
-    local 8-bit encoding. Therefore using qPrintable for logging
-    strings is only safe if the argument contains only ASCII
-    characters.
-
-    \sa qDebug(), qWarning(), qCritical(), qFatal()
+    \sa qPrintable(), qDebug(), qWarning(), qCritical(), qFatal()
 */
 
 /*!
diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h
index a9621e744c..80c9992e25 100644
--- a/src/corelib/global/qglobal.h
+++ b/src/corelib/global/qglobal.h
@@ -645,6 +645,10 @@ inline void qUnused(T &x) { (void)x; }
 #  define qPrintable(string) QString(string).toLocal8Bit().constData()
 #endif
 
+#ifndef qUtf8Printable
+#  define qUtf8Printable(string) QString(string).toUtf8().constData()
+#endif
+
 class QString;
 Q_CORE_EXPORT QString qt_error_string(int errorCode = -1);