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authorBrad King <brad.king@kitware.com>2014-06-02 14:44:28 (GMT)
committerCMake Topic Stage <kwrobot@kitware.com>2014-06-02 14:44:28 (GMT)
commit7b888a56242f451ce6771145f5864ec51abd0885 (patch)
tree295f19d036005fb1d8f338f106db222cb93c5d5b /Help
parent4b8ec7514a4214b526687b12ed2f310697d395ad (diff)
parent60a981ea8eda7a5af679ca3b2e4d54bc50ad61b3 (diff)
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Merge topic 'feature-extensions-by-default'
60a981ea Features: Enable compiler extensions by default.
Diffstat (limited to 'Help')
-rw-r--r--Help/command/target_compile_features.rst2
-rw-r--r--Help/manual/cmake-compile-features.7.rst25
-rw-r--r--Help/prop_tgt/CXX_EXTENSIONS.rst3
-rw-r--r--Help/prop_tgt/CXX_STANDARD.rst6
-rw-r--r--Help/prop_tgt/C_EXTENSIONS.rst3
-rw-r--r--Help/prop_tgt/C_STANDARD.rst6
6 files changed, 22 insertions, 23 deletions
diff --git a/Help/command/target_compile_features.rst b/Help/command/target_compile_features.rst
index a6503db..29a8b41 100644
--- a/Help/command/target_compile_features.rst
+++ b/Help/command/target_compile_features.rst
@@ -11,7 +11,7 @@ Specify compiler features required when compiling a given target. If the
feature is not listed in the :variable:`CMAKE_C_COMPILE_FEATURES` variable
or :variable:`CMAKE_CXX_COMPILE_FEATURES` variable,
then an error will be reported by CMake. If the use of the feature requires
-an additional compiler flag, such as ``-std=c++11``, the flag will be added
+an additional compiler flag, such as ``-std=gnu++11``, the flag will be added
automatically.
The ``INTERFACE``, ``PUBLIC`` and ``PRIVATE`` keywords are required to
diff --git a/Help/manual/cmake-compile-features.7.rst b/Help/manual/cmake-compile-features.7.rst
index c014846..d4bbecc 100644
--- a/Help/manual/cmake-compile-features.7.rst
+++ b/Help/manual/cmake-compile-features.7.rst
@@ -47,7 +47,7 @@ be compiled with compiler support for the
In processing the requirement for the ``cxx_constexpr`` feature,
:manual:`cmake(1)` will ensure that the in-use C++ compiler is capable
-of the feature, and will add any necessary flags such as ``-std=c++11``
+of the feature, and will add any necessary flags such as ``-std=gnu++11``
to the compile lines of C++ files in the ``mylib`` target. A
``FATAL_ERROR`` is issued if the compiler is not capable of the
feature.
@@ -59,8 +59,8 @@ for each target.
Such compile flags are added even if the compiler supports the
particular feature without the flag. For example, the GNU compiler
-supports variadic templates (with a warning) even if ``-std=c++98`` is
-used. CMake adds the ``-std=c++11`` flag if ``cxx_variadic_templates``
+supports variadic templates (with a warning) even if ``-std=gnu++98`` is
+used. CMake adds the ``-std=gnu++11`` flag if ``cxx_variadic_templates``
is specified as a requirement.
In the above example, ``mylib`` requires ``cxx_constexpr`` when it
@@ -76,7 +76,7 @@ known feature), that may be specified with the ``PUBLIC`` or
# cxx_constexpr is a usage-requirement
target_compile_features(mylib PUBLIC cxx_constexpr)
- # main.cpp will be compiled with -std=c++11 on GNU for cxx_constexpr.
+ # main.cpp will be compiled with -std=gnu++11 on GNU for cxx_constexpr.
add_executable(myexe main.cpp)
target_link_libraries(myexe mylib)
@@ -84,16 +84,13 @@ Feature requirements are evaluated transitively by consuming the link
implementation. See :manual:`cmake-buildsystem(7)` for more on
transitive behavior of build properties and usage requirements.
-Note that new use of compile feature requirements may expose
-cross-platform bugs in user code. For example, the GNU compiler uses the
-``gnu++98`` language by default as of GCC version 4.8. User code may
-be relying on that by expecting the ``typeof`` GNU extension to work.
-However, if the :command:`target_compile_features` command is used to
-specify the requirement for ``cxx_constexpr``, a ``-std=c++11`` flag may
-be added, and the ``typeof`` extension would no longer be available. The
-solution is to specify that compiler extensions are relied upon by setting
-the :prop_tgt:`CXX_EXTENSIONS` target property to ``ON`` when starting to
-use the :command:`target_compile_features` command.
+Because the :prop_tgt:`CXX_EXTENSIONS` target property is ``ON`` by default,
+CMake uses extended variants of language dialects by default, such as
+``-std=gnu++11`` instead of ``-std=c++11``. That target property may be
+set to ``OFF`` to use the non-extended variant of the dialect flag. Note
+that because most compilers enable extensions by default, this could
+expose cross-platform bugs in user code or in the headers of third-party
+dependencies.
Optional Compile Features
=========================
diff --git a/Help/prop_tgt/CXX_EXTENSIONS.rst b/Help/prop_tgt/CXX_EXTENSIONS.rst
index d7f87a4..67c5cb0 100644
--- a/Help/prop_tgt/CXX_EXTENSIONS.rst
+++ b/Help/prop_tgt/CXX_EXTENSIONS.rst
@@ -5,7 +5,8 @@ Boolean specifying whether compiler specific extensions are requested.
This property specifies whether compiler specific extensions should be
used. For some compilers, this results in adding a flag such
-as ``-std=gnu++11`` instead of ``-std=c++11`` to the compile line.
+as ``-std=gnu++11`` instead of ``-std=c++11`` to the compile line. This
+property is ``ON`` by default.
See the :manual:`cmake-compile-features(7)` manual for information on
compile features.
diff --git a/Help/prop_tgt/CXX_STANDARD.rst b/Help/prop_tgt/CXX_STANDARD.rst
index 8f299bb..b50cdf9 100644
--- a/Help/prop_tgt/CXX_STANDARD.rst
+++ b/Help/prop_tgt/CXX_STANDARD.rst
@@ -5,7 +5,7 @@ The C++ standard whose features are requested to build this target.
This property specifies the C++ standard whose features are requested
to build this target. For some compilers, this results in adding a
-flag such as ``-std=c++11`` to the compile line.
+flag such as ``-std=gnu++11`` to the compile line.
Supported values are ``98`` and ``11``.
@@ -17,9 +17,9 @@ means that using:
set_property(TARGET tgt PROPERTY CXX_STANDARD 11)
-with a compiler which does not support ``-std=c++11`` or an equivalent
+with a compiler which does not support ``-std=gnu++11`` or an equivalent
flag will not result in an error or warning, but will instead add the
-``-std=c++98`` flag if supported. This "decay" behavior may be controlled
+``-std=gnu++98`` flag if supported. This "decay" behavior may be controlled
with the :prop_tgt:`CXX_STANDARD_REQUIRED` target property.
See the :manual:`cmake-compile-features(7)` manual for information on
diff --git a/Help/prop_tgt/C_EXTENSIONS.rst b/Help/prop_tgt/C_EXTENSIONS.rst
index 0772ecc..dc48cc6 100644
--- a/Help/prop_tgt/C_EXTENSIONS.rst
+++ b/Help/prop_tgt/C_EXTENSIONS.rst
@@ -5,7 +5,8 @@ Boolean specifying whether compiler specific extensions are requested.
This property specifies whether compiler specific extensions should be
used. For some compilers, this results in adding a flag such
-as ``-std=gnu11`` instead of ``-std=c11`` to the compile line.
+as ``-std=gnu11`` instead of ``-std=c11`` to the compile line. This
+property is ``ON`` by default.
See the :manual:`cmake-compile-features(7)` manual for information on
compile features.
diff --git a/Help/prop_tgt/C_STANDARD.rst b/Help/prop_tgt/C_STANDARD.rst
index a0c939a..88ca926 100644
--- a/Help/prop_tgt/C_STANDARD.rst
+++ b/Help/prop_tgt/C_STANDARD.rst
@@ -5,7 +5,7 @@ The C standard whose features are requested to build this target.
This property specifies the C standard whose features are requested
to build this target. For some compilers, this results in adding a
-flag such as ``-std=c11`` to the compile line.
+flag such as ``-std=gnu11`` to the compile line.
Supported values are ``90``, ``99`` and ``11``.
@@ -17,9 +17,9 @@ means that using:
set_property(TARGET tgt PROPERTY C_STANDARD 11)
-with a compiler which does not support ``-std=c11`` or an equivalent
+with a compiler which does not support ``-std=gnu11`` or an equivalent
flag will not result in an error or warning, but will instead add the
-``-std=c99`` or ``-std=c90`` flag if supported. This "decay" behavior may
+``-std=gnu99`` or ``-std=gnu90`` flag if supported. This "decay" behavior may
be controlled with the :prop_tgt:`C_STANDARD_REQUIRED` target property.
See the :manual:`cmake-compile-features(7)` manual for information on