Mame: Compilation error on older MacOS/Xcode releases, for file 'src/osd/modules/file/posixfile.cpp'

[mascguy]

Mame 0.226 fails to build on MacOS 10.8 and Xcode 5.x, due to compilation errors in file src/osd/modules/files/posixfile.cpp.

Here's one example:

In file included from ../../../../../src/osd/modules/file/posixfile.cpp:41:
In file included from ../../../../../src/osd/modules/file/posixfile.h:12:
In file included from ../../../../../src/osd/osdcore.h:17:
In file included from ../../../../../src/lib/util/strformat.h:174:
In file included from ../../../../../src/lib/util/vecstream.h:25:
In file included from /opt/local/libexec/llvm-9.0/bin/../include/c++/v1/istream:163:
In file included from /opt/local/libexec/llvm-9.0/bin/../include/c++/v1/ostream:140:
/opt/local/libexec/llvm-9.0/bin/../include/c++/v1/locale:1455:16: error: use of undeclared identifier 'snprintf_l'; did you mean 'vswprintf_l'?
    int __nc = __libcpp_snprintf_l(__nar, sizeof(__nar), _LIBCPP_GET_C_LOCALE, __fmt, __v);
               ^

Root cause is the preprocessor logic within C header file /usr/include/xlocale/_stdio.h, determining whether additional stdio functions are defined. One of those being snprintf_l().

Findings:

• In later MacOS/Xcode releases, the logic is #if __DARWIN_C_LEVEL >= 200112L || defined(__cplusplus). The latter condition ensures we don't have to worry about __DARWIN_C_LEVEL.
• But under MacOS 10.8 and Xcode 5.x, the logic is simply #if __DARWIN_C_LEVEL >= 200112L, with no awareness of C++ code. This breaks the Mame build.

The fix is easy: Define _DARWIN_C_SOURCE in posixfile.cpp, before including any library headers:

--- src/osd/modules/file/posixfile.cpp	2020-12-08 16:14:00.000000000 -0500
+++ src/osd/modules/file/posixfile.cpp	2020-12-08 16:15:00.000000000 -0500
@@ -37,6 +37,11 @@
 #endif
 #endif

+// Fix for MacOS compilation errors
+#if defined(__APPLE__) && !defined(_DARWIN_C_SOURCE)
+#define _DARWIN_C_SOURCE
+#endif
+
 // MAME headers
 #include "posixfile.h"
 #include "unicode.h"

I'll submit a pull request with the requested change.