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[WIP] Detect presence of flockfile #4737

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[WIP] Detect presence of flockfile #4737

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[DRAFT, WIP] Detect presence of flockfile
mvastola Apr 9, 2026
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mvastola Apr 9, 2026
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16 changes: 16 additions & 0 deletions CMakeLists.txt
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Original file line number Diff line number Diff line change
Expand Up @@ -128,6 +128,7 @@ endif ()
list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/support/cmake")

include(CheckCXXCompilerFlag)
include(CheckCXXSourceCompiles)
include(JoinPaths)

if (FMT_MASTER_PROJECT AND NOT DEFINED CMAKE_CXX_VISIBILITY_PRESET)
Expand Down Expand Up @@ -307,6 +308,21 @@ else ()
message(WARNING "Feature cxx_std_11 is unknown for the CXX compiler")
endif ()

check_cxx_source_compiles(
[[
#include <stdio.h>
int main() {
// Use stdout just to prove we can pass a FILE* to it
flockfile(stdout);
funlockfile(stdout);
return 0;
}
]]
HAVE_FLOCKFILE_COMPILE_TEST)
target_compile_definitions(
fmt
PRIVATE FMT_HAVE_FLOCKFILE_COMPILE_TEST=$<BOOL:HAVE_FLOCKFILE_COMPILE_TEST>)

# Set FMT_LIB_NAME for pkg-config fmt.pc. We cannot use the OUTPUT_NAME target
# property because it's not set by default.
set(FMT_LIB_NAME fmt)
Expand Down
6 changes: 5 additions & 1 deletion include/fmt/format-inl.h
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Expand Up @@ -1490,7 +1490,11 @@ template <typename F> auto getc_unlocked(F* f) -> decltype(_fgetc_nolock(f)) {
#endif

#ifndef FMT_USE_FLOCKFILE
# define FMT_USE_FLOCKFILE 1
# ifdef FMT_HAVE_FLOCKFILE_COMPILE_TEST
# define FMT_USE_FLOCKFILE FMT_HAVE_FLOCKFILE_COMPILE_TEST
# else
# define FMT_USE_FLOCKFILE 1
# endif
#endif

template <typename F = FILE, typename Enable = void>
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