1CMAKE-COMPILE-FEATURES(7) CMake CMAKE-COMPILE-FEATURES(7)
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6 cmake-compile-features - CMake Compile Features Reference
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9 Project source code may depend on, or be conditional on, the availabil‐
10 ity of certain features of the compiler. There are three use-cases
11 which arise: Compile Feature Requirements, Optional Compile Features
12 and Conditional Compilation Options.
13 While features are typically specified in programming language stan‐
15 dards, CMake provides a primary user interface based on granular han‐
16 dling of the features, not the language standard that introduced the
17 feature.
18 The CMAKE_C_KNOWN_FEATURES, CMAKE_CUDA_KNOWN_FEATURES, and
20 CMAKE_CXX_KNOWN_FEATURES global properties contain all the features
21 known to CMake, regardless of compiler support for the feature. The
22 CMAKE_C_COMPILE_FEATURES, CMAKE_CUDA_COMPILE_FEATURES , and
23 CMAKE_CXX_COMPILE_FEATURES variables contain all features CMake knows
24 are known to the compiler, regardless of language standard or compile
25 flags needed to use them.
26 Features known to CMake are named mostly following the same convention
28 as the Clang feature test macros. There are some exceptions, such as
29 CMake using cxx_final and cxx_override instead of the single cxx_over‐
30 ride_control used by Clang.
31 Note that there are no separate compile features properties or vari‐
33 ables for the OBJC or OBJCXX languages. These are based off C or C++
34 respectively, so the properties and variables for their corresponding
35 base language should be used instead.
36
38 Compile feature requirements may be specified with the target_com‐
39 pile_features() command. For example, if a target must be compiled
40 with compiler support for the cxx_constexpr feature:
41 add_library(mylib requires_constexpr.cpp)
43 target_compile_features(mylib PRIVATE cxx_constexpr)
44 In processing the requirement for the cxx_constexpr feature, cmake(1)
46 will ensure that the in-use C++ compiler is capable of the feature, and
47 will add any necessary flags such as -std=gnu++11 to the compile lines
48 of C++ files in the mylib target. A FATAL_ERROR is issued if the com‐
49 piler is not capable of the feature.
50 The exact compile flags and language standard are deliberately not part
52 of the user interface for this use-case. CMake will compute the appro‐
53 priate compile flags to use by considering the features specified for
54 each target.
55 Such compile flags are added even if the compiler supports the particu‐
57 lar feature without the flag. For example, the GNU compiler supports
58 variadic templates (with a warning) even if -std=gnu++98 is used.
59 CMake adds the -std=gnu++11 flag if cxx_variadic_templates is specified
60 as a requirement.
61 In the above example, mylib requires cxx_constexpr when it is built it‐
63 self, but consumers of mylib are not required to use a compiler which
64 supports cxx_constexpr. If the interface of mylib does require the
65 cxx_constexpr feature (or any other known feature), that may be speci‐
66 fied with the PUBLIC or INTERFACE signatures of target_compile_fea‐
67 tures():
68 add_library(mylib requires_constexpr.cpp)
70 # cxx_constexpr is a usage-requirement
71 target_compile_features(mylib PUBLIC cxx_constexpr)
72 # main.cpp will be compiled with -std=gnu++11 on GNU for cxx_constexpr.
74 add_executable(myexe main.cpp)
75 target_link_libraries(myexe mylib)
76 Feature requirements are evaluated transitively by consuming the link
78 implementation. See cmake-buildsystem(7) for more on transitive behav‐
79 ior of build properties and usage requirements.
80 Requiring Language Standards
82 In projects that use a large number of commonly available features from
83 a particular language standard (e.g. C++ 11) one may specify a
84 meta-feature (e.g. cxx_std_11) that requires use of a compiler mode
85 that is at minimum aware of that standard, but could be greater. This
86 is simpler than specifying all the features individually, but does not
87 guarantee the existence of any particular feature. Diagnosis of use of
88 unsupported features will be delayed until compile time.
89 For example, if C++ 11 features are used extensively in a project's
91 header files, then clients must use a compiler mode that is no less
92 than C++ 11. This can be requested with the code:
93 target_compile_features(mylib PUBLIC cxx_std_11)
95 In this example, CMake will ensure the compiler is invoked in a mode of
97 at-least C++ 11 (or C++ 14, C++ 17, ...), adding flags such as
98 -std=gnu++11 if necessary. This applies to sources within mylib as
99 well as any dependents (that may include headers from mylib).
100 Availability of Compiler Extensions
102 Because the CXX_EXTENSIONS target property is ON by default, CMake uses
103 extended variants of language dialects by default, such as -std=gnu++11
104 instead of -std=c++11. That target property may be set to OFF to use
105 the non-extended variant of the dialect flag. Note that because most
106 compilers enable extensions by default, this could expose cross-plat‐
107 form bugs in user code or in the headers of third-party dependencies.
108
110 Compile features may be preferred if available, without creating a hard
111 requirement. This can be achieved by not specifying features with
112 target_compile_features() and instead checking the compiler capabili‐
113 ties with preprocessor conditions in project code.
114 In this use-case, the project may wish to establish a particular lan‐
116 guage standard if available from the compiler, and use preprocessor
117 conditions to detect the features actually available. A language stan‐
118 dard may be established by Requiring Language Standards using tar‐
119 get_compile_features() with meta-features like cxx_std_11, or by set‐
120 ting the CXX_STANDARD target property or CMAKE_CXX_STANDARD variable.
121 See also policy CMP0120 and legacy documentation on Example Usage of
123 the deprecated WriteCompilerDetectionHeader module.
124
126 Libraries may provide entirely different header files depending on re‐
127 quested compiler features.
128 For example, a header at with_variadics/interface.h may contain:
130 template<int I, int... Is>
132 struct Interface;
133 template<int I>
135 struct Interface<I>
136 {
137 static int accumulate()
138 {
139 return I;
140 }
141 };
142 template<int I, int... Is>
144 struct Interface
145 {
146 static int accumulate()
147 {
148 return I + Interface<Is...>::accumulate();
149 }
150 };
151 while a header at no_variadics/interface.h may contain:
153 template<int I1, int I2 = 0, int I3 = 0, int I4 = 0>
155 struct Interface
156 {
157 static int accumulate() { return I1 + I2 + I3 + I4; }
158 };
159 It may be possible to write an abstraction interface.h header contain‐
161 ing something like:
162 #ifdef HAVE_CXX_VARIADIC_TEMPLATES
164 #include "with_variadics/interface.h"
165 #else
166 #include "no_variadics/interface.h"
167 #endif
168 However this could be unmaintainable if there are many files to ab‐
170 stract. What is needed is to use alternative include directories de‐
171 pending on the compiler capabilities.
172 CMake provides a COMPILE_FEATURES generator expression to implement
174 such conditions. This may be used with the build-property commands
175 such as target_include_directories() and target_link_libraries() to set
176 the appropriate buildsystem properties:
177 add_library(foo INTERFACE)
179 set(with_variadics ${CMAKE_CURRENT_SOURCE_DIR}/with_variadics)
180 set(no_variadics ${CMAKE_CURRENT_SOURCE_DIR}/no_variadics)
181 target_include_directories(foo
182 INTERFACE
183 "$<$<COMPILE_FEATURES:cxx_variadic_templates>:${with_variadics}>"
184 "$<$<NOT:$<COMPILE_FEATURES:cxx_variadic_templates>>:${no_variadics}>"
185 )
186 Consuming code then simply links to the foo target as usual and uses
188 the feature-appropriate include directory
189 add_executable(consumer_with consumer_with.cpp)
191 target_link_libraries(consumer_with foo)
192 set_property(TARGET consumer_with CXX_STANDARD 11)
193 add_executable(consumer_no consumer_no.cpp)
195 target_link_libraries(consumer_no foo)
196
198 CMake is currently aware of the C++ standards and compile features
199 available from the following compiler ids as of the versions specified
200 for each:
201 • AppleClang: Apple Clang for Xcode versions 4.4+.
203 • Clang: Clang compiler versions 2.9+.
205 • GNU: GNU compiler versions 4.4+.
207 • MSVC: Microsoft Visual Studio versions 2010+.
209 • SunPro: Oracle SolarisStudio versions 12.4+.
211 • Intel: Intel compiler versions 12.1+.
213 CMake is currently aware of the C standards and compile features avail‐
215 able from the following compiler ids as of the versions specified for
216 each:
217 • all compilers and versions listed above for C++.
219 • GNU: GNU compiler versions 3.4+
221 CMake is currently aware of the C++ standards and their associated
223 meta-features (e.g. cxx_std_11) available from the following compiler
224 ids as of the versions specified for each:
225 • Cray: Cray Compiler Environment version 8.1+.
227 • PGI: PGI version 12.10+.
229 • NVHPC: NVIDIA HPC compilers version 11.0+.
231 • TI: Texas Instruments compiler.
233 • XL: IBM XL version 10.1+.
235 CMake is currently aware of the C standards and their associated
237 meta-features (e.g. c_std_99) available from the following compiler ids
238 as of the versions specified for each:
239 • all compilers and versions listed above with only meta-features for
241 C++.
242 CMake is currently aware of the CUDA standards and their associated
244 meta-features (e.g. cuda_std_11) available from the following compiler
245 ids as of the versions specified for each:
246 • Clang: Clang compiler 5.0+.
248 • NVIDIA: NVIDIA nvcc compiler 7.5+.
250
252 2000-2021 Kitware, Inc. and Contributors
2533.20.3 May 30, 2021 CMAKE-COMPILE-FEATURES(7)