Add C11 API with type-safe formatting (#4663) (#4671)

CMakeLists.txt

@@ -533,3 +533,51 @@ if (FMT_MASTER_PROJECT AND EXISTS ${gitignore})
   set(CPACK_RESOURCE_FILE_README ${PROJECT_SOURCE_DIR}/README.md)
   include(CPack)
 endif ()
+
+# C API Wrapper
+add_library(fmt_c STATIC src/fmt-c.cc)
+
+target_compile_features(fmt_c PUBLIC cxx_std_11)
+target_link_libraries(fmt_c PUBLIC fmt::fmt)
+
+target_include_directories(fmt_c PUBLIC
+        $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
+        $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+)
+
+set_target_properties(fmt_c PROPERTIES
+        VERSION ${FMT_VERSION}
+        SOVERSION ${CPACK_PACKAGE_VERSION_MAJOR}
+        DEBUG_POSTFIX "${CMAKE_DEBUG_POSTFIX}"
+        C_VISIBILITY_PRESET default
+        CXX_VISIBILITY_PRESET hidden
+)
+
+add_library(fmt::fmt_c ALIAS fmt_c)
+if(FMT_INSTALL)
+  install(TARGETS fmt_c
+          EXPORT fmt-targets
+          ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
+)
+  install(FILES include/fmt/fmt-c.h
+          DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/fmt
+)
+endif()
+
+if(FMT_TEST)
+  enable_language(C)
+  message(STATUS "Adding C API test executable")
+
+  add_executable(test-c-api test/test_c.c)
+  target_link_libraries(test-c-api PRIVATE fmt::fmt_c)
+  set_target_properties(test-c-api PROPERTIES
+          C_STANDARD 11
+          C_STANDARD_REQUIRED ON
+  )
+  if(MSVC)
+    target_compile_options(test-c-api PRIVATE /Zc:preprocessor)
+  endif()
+
+  add_test(NAME c-api-test COMMAND test-c-api)
+endif()
+