如何检查编译器对特定关键字/属性的支持？CMake检测C编译器特性方法

Great question! Checking compiler support for specific keywords or attributes is a must for cross-platform C development, and CMake gives you all the tools you need to do this reliably. Let's break this down step by step, covering both general strategies and your specific use cases.

General Ways to Check Compiler Support #

Before diving into your specific checks, here are the two most reliable approaches for verifying compiler features:

• Leverage compiler-specific predefined macros: Most compilers define macros (like __GNUC__ for GCC/clang, _MSC_VER for MSVC) that let you conditionally check for compiler families and versions directly in your code.
• Test compilation of minimal code snippets: This is the gold standard—CMake provides modules like CheckCSourceCompiles that attempt to compile a tiny piece of code using the feature you're checking. If it compiles successfully, you know the feature is supported.

Detecting Visibility Attributes (__hidden / visibility("hidden")) #

First, note that __hidden is less common; most compilers use attribute-based syntax instead:

• GCC, clang, and other GNU-compatible compilers use __attribute__((visibility("hidden")))
• MSVC uses __declspec(hidden)

Here's how to detect these with CMake:

Step 1: Use CMake's CheckCSourceCompiles Module #

Add this to your CMakeLists.txt:

include(CheckCSourceCompiles)

# Check for GCC-style visibility attribute
check_c_source_compiles("
#include <stdio.h>
__attribute__((visibility(\"hidden\"))) void test_hidden() {}
int main() { test_hidden(); return 0; }
" HAVE_VISIBILITY_HIDDEN)

# Check for MSVC-style __declspec(hidden)
check_c_source_compiles("
#include <stdio.h>
__declspec(hidden) void test_hidden() {}
int main() { test_hidden(); return 0; }
" HAVE_DECLSPEC_HIDDEN)

# Define a unified macro for your code to use
if(HAVE_VISIBILITY_HIDDEN)
    add_compile_definitions(HAVE_HIDDEN_ATTRIBUTE=1)
    add_compile_definitions(HIDDEN_ATTRIBUTE="__attribute__((visibility(\"hidden\")))")
elif(HAVE_DECLSPEC_HIDDEN)
    add_compile_definitions(HAVE_HIDDEN_ATTRIBUTE=1)
    add_compile_definitions(HIDDEN_ATTRIBUTE="__declspec(hidden)")
else()
    # Fallback to empty if no support
    add_compile_definitions(HIDDEN_ATTRIBUTE="")
endif()

Step 2: Use the Macro in Your C Code #

Now you can use HIDDEN_ATTRIBUTE to mark functions/variables with hidden visibility portably:

HIDDEN_ATTRIBUTE void my_internal_function() {
    // Implementation
}

Detecting the restrict Keyword #

restrict is a C99 standard keyword for optimizing pointer access, but some compilers use alternatives (like MSVC's __restrict for older versions). Here's how to detect support:

CMake Check Code #

Add this to your CMakeLists.txt:

# Check for standard C99 restrict
check_c_source_compiles("
#include <stdio.h>
void test_restrict(int* restrict ptr) { *ptr = 0; }
int main() { int x; test_restrict(&x); return 0; }
" HAVE_RESTRICT)

# Check for MSVC's __restrict as a fallback
check_c_source_compiles("
#include <stdio.h>
void test_restrict(int* __restrict ptr) { *ptr = 0; }
int main() { int x; test_restrict(&x); return 0; }
" HAVE___RESTRICT)

# Define a unified macro for your code
if(HAVE_RESTRICT)
    add_compile_definitions(RESTRICT_KEYWORD="restrict")
elif(HAVE___RESTRICT)
    add_compile_definitions(RESTRICT_KEYWORD="__restrict")
else()
    add_compile_definitions(RESTRICT_KEYWORD="")
endif()

Use the Macro in Your Code #

Now you can write portable code with the restrict keyword:

void process_data(int* RESTRICT_KEYWORD input, int* RESTRICT_KEYWORD output, size_t size) {
    // Optimized implementation that assumes no pointer aliasing
}

Bonus: Global Visibility Control #

If you want to set hidden visibility for all symbols (common in shared libraries), you can check for compiler flags like -fvisibility=hidden (GCC/clang) with CMake's CheckCCompilerFlag module:

include(CheckCCompilerFlag)
check_c_compiler_flag("-fvisibility=hidden" SUPPORTS_FVISIBILITY_HIDDEN)
if(SUPPORTS_FVISIBILITY_HIDDEN)
    add_compile_options(-fvisibility=hidden)
endif()

This complements the per-symbol attribute checks if you want a global default.

内容的提问来源于stack exchange，提问作者einpoklum