QtGlobal: (new) qEnvironmentVariableIs{Set,Empty}()

These functions are a faster version of {,!}qgetenv().is{Null,Empty}(),
a common pattern in Qt code.

Their main advantage is that they don't need to allocate memory, so
they can be used in noexcept functions, or dynamic initialisation of
namespace-scope statics, because throwing in these contexts invokes
std::terminate().

Change-Id: I651c5bd72f450b5d7df76590f8791572fe992af5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 56 insertions, 0 deletions

diff --git a/src/corelib/global/qglobal.cpp b/src/corelib/global/qglobal.cpp
index 17cb9db86f..b60e7495c6 100644
--- a/src/corelib/global/qglobal.cpp
+++ b/src/corelib/global/qglobal.cpp
@@ -2085,6 +2085,62 @@ QByteArray qgetenv(const char *varName)
 
 /*!
     \relates <QtGlobal>
+    \internal
+
+    This function checks whether the environment variable \a varName
+    is empty.
+
+    Equivalent to
+    \code
+    qgetenv(varName).isEmpty()
+    \endcode
+    except that it's potentially much faster, and can't throw exceptions.
+
+    \sa qgetenv(), qEnvironmentVariableIsSet()
+*/
+bool qEnvironmentVariableIsEmpty(const char *varName) Q_DECL_NOEXCEPT
+{
+#if defined(_MSC_VER) && _MSC_VER >= 1400
+    // we provide a buffer that can only hold the empty string, so
+    // when the env.var isn't empty, we'll get an ERANGE error (buffer
+    // too small):
+    size_t dummy;
+    char buffer = '\0';
+    return getenv_s(&dummy, &buffer, 1, varName) != ERANGE;
+#else
+    const char * const value = ::getenv(varName);
+    return !value || !*value;
+#endif
+}
+
+/*!
+    \relates <QtGlobal>
+    \internal
+
+    This function checks whether the environment variable \a varName
+    is set.
+
+    Equivalent to
+    \code
+    !qgetenv(varName).isNull()
+    \endcode
+    except that it's potentially much faster, and can't throw exceptions.
+
+    \sa qgetenv(), qEnvironmentVariableIsEmpty()
+*/
+bool qEnvironmentVariableIsSet(const char *varName) Q_DECL_NOEXCEPT
+{
+#if defined(_MSC_VER) && _MSC_VER >= 1400
+    size_t requiredSize = 0;
+    (void)getenv_s(&requiredSize, 0, 0, varName);
+    return requiredSize != 0;
+#else
+    return ::getenv(varName) != 0;
+#endif
+}
+
+/*!
+    \relates <QtGlobal>
 
     This function sets the \a value of the environment variable named
     \a varName. It will create the variable if it does not exist. It