# 2020-07-22 starting at FreeFileSync 10.25 in 2020-06, we need g++-10 to compile but all EL targets (6, 7, and 8) do not have gcc 10 so this patch is not usable as is. But it should get the gtk3 fix if any CentOS targets get gcc-10.
The cstddef discovery is from https://stackoverflow.com/questions/52567517/freefilesync-c-error-byte-is-not-a-member-of-std
Some changes just make the application work better in an installed setting (e.g., the hard-coded resouce path).
Tricking the wxWidgets ABI version comes from https://stackoverflow.com/questions/45123664/wxwidgets-runtime-error-mismatch-version/47822976#47822976
FreeFileSync 10.11 updated the default compile flags to -std=c++2a, but this fails on gcc 4.8.5 on el7. Reverting to -std=c++17 allows the application to compile.
diff -Naur 10.13-0/FreeFileSync/Source/ffs_paths.cpp 10.13-1/FreeFileSync/Source/ffs_paths.cpp
--- 10.13-0/FreeFileSync/Source/ffs_paths.cpp	2019-06-14 20:23:07.615661499 -0400
+++ 10.13-1/FreeFileSync/Source/ffs_paths.cpp	2019-06-14 20:36:28.178274292 -0400
@@ -55,7 +55,8 @@
 
 Zstring fff::getResourceDirPf()
 {
-    return getProcessParentFolderPath() + FILE_NAME_SEPARATOR + Zstr("Resources") + FILE_NAME_SEPARATOR;
+    // For Fedora, EL and Devuan, install to /usr/share/freefilesync specificly
+    return Zstr("/usr/share/freefilesync/");
 }
 
 
diff -Naur -x '*.orig' -x '*.rej' -x '*.swp' 10.11-0/FreeFileSync/Source/Makefile 10.11-1/FreeFileSync/Source/Makefile
--- 10.11-0/FreeFileSync/Source/Makefile	2019-04-12 07:59:45.042147902 -0400
+++ 10.18-1/FreeFileSync/Source/Makefile	2019-11-21 20:59:25.548277619 -0500
@@ -1,10 +1,10 @@
-exeName = FreeFileSync_$(shell arch)
+exeName = FreeFileSync
 
-cxxFlags = -std=c++2a -pipe -DWXINTL_NO_GETTEXT_MACRO -I../.. -I../../zenXml -include "zen/i18n.h" -include "zen/warn_static.h" \
+cxxFlags = -std=c++17 -pipe -DWXINTL_NO_GETTEXT_MACRO -I../.. -I../../zenXml -include "zen/i18n.h" -include "zen/warn_static.h" \
            -Wall -Wfatal-errors -Wmissing-include-dirs -Wswitch-enum -Wcast-align -Wshadow -Wnon-virtual-dtor \
-           -O3 -DNDEBUG `wx-config --cxxflags --debug=no` -pthread
+           -O3 -DNDEBUG -fPIC `wx-config --version=3.0 --cxxflags --debug=no` -pthread
 
-linkFlags = -s -no-pie `wx-config --libs std, aui --debug=no` -pthread
+linkFlags = -s -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -Wl,-z,relro  -no-pie `wx-config --version=3.0 --libs std, aui --debug=no | sed -r -e 's/-[^[:space:]]+web[^[:space:]]+//;'` -lz -pthread
 
 
 cxxFlags  += `pkg-config --cflags openssl`
@@ -17,6 +17,7 @@
 linkFlags += `pkg-config --libs   libssh2`

 cxxFlags  += `pkg-config --cflags gtk+-2.0`
+linkFlags += `pkg-config --libs   gtk+-2.0`
 #treat as system headers so that warnings are hidden:
 cxxFlags  += -isystem/usr/include/gtk-2.0

diff -Naur -x '*.orig' -x '*.rej' -x '*.swp' 10.11-0/FreeFileSync/Source/RealTimeSync/application.h 10.11-1/FreeFileSync/Source/RealTimeSync/application.h
--- 10.11-0/FreeFileSync/Source/RealTimeSync/application.h	2019-04-12 07:59:45.035147580 -0400
+++ 10.11-1/FreeFileSync/Source/RealTimeSync/application.h	2019-04-12 10:19:57.227913415 -0400
@@ -7,6 +7,8 @@
 #ifndef APPLICATION_H_18506781708176342677
 #define APPLICATION_H_18506781708176342677
 
+#define __GXX_ABI_VERSION 1002
+
 #include <wx/app.h>
 
 
diff -Naur -x '*.orig' -x '*.rej' -x '*.swp' 10.11-0/FreeFileSync/Source/RealTimeSync/Makefile 10.11-1/FreeFileSync/Source/RealTimeSync/Makefile
--- 10.11-0/FreeFileSync/Source/RealTimeSync/Makefile	2019-04-12 07:59:45.008146336 -0400
+++ 10.18-1/FreeFileSync/Source/RealTimeSync/Makefile	2019-11-22 10:14:04.326175203 -0500
@@ -1,13 +1,14 @@
-exeName = RealTimeSync_$(shell arch)
+exeName = RealTimeSync

-cxxFlags = -std=c++2a -pipe -DWXINTL_NO_GETTEXT_MACRO -I../../.. -I../../../zenXml -include "zen/i18n.h" -include "zen/warn_static.h" \
+cxxFlags = -std=c++17 -pipe -DWXINTL_NO_GETTEXT_MACRO -I../../.. -I../../../zenXml -include "zen/i18n.h" -include "zen/warn_static.h" \
            -Wall -Wfatal-errors -Wmissing-include-dirs -Wswitch-enum -Wcast-align -Wshadow -Wnon-virtual-dtor \
-           -O3 -DNDEBUG `wx-config --cxxflags --debug=no` -pthread
+           -O3 -DNDEBUG -fPIC `wx-config --version=3.0 --cxxflags --debug=no` -pthread

-linkFlags = -s -no-pie `wx-config --libs std, aui --debug=no` -pthread
+linkFlags = -s -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -no-pie `wx-config --version=3.0 --cxxflags --libs std, aui --debug=no | sed -r -e 's/-[^[:space:]]+web[^[:space:]]+//;'` -lz -pthread

 #Gtk - support "no button border"
 cxxFlags  += `pkg-config --cflags gtk+-2.0`
+linkFlags += `pkg-config --libs   gtk+-2.0`
 #treat as system headers so that warnings are hidden:
 cxxFlags  += -isystem/usr/include/gtk-2.0

diff -x '*.swp' -x '.git*' -x '*.orig' -x '*.rej' -Naur 10.19-0/FreeFileSync/Source/ui/small_dlgs.cpp 11.12-1/FreeFileSync/Source/ui/small_dlgs.cpp
--- 10.11-0/FreeFileSync/Source/ui/small_dlgs.cpp	2019-12-27 07:56:06.714625467 -0500
+++ 11.12-1/FreeFileSync/Source/ui/small_dlgs.cpp  2021-07-15 09:03:57.753183052 -0400
@@ -93,6 +93,8 @@
     build += LTR_MARK; //fix Arabic
     build += utfTo<wxString>(cpuArchName);
 
+    build += L" for CentOS";
+
     build += SPACED_BULLET;
     build += utfTo<wxString>(formatTime(formatDateTag, getCompileTime()));
 
diff -Naur -x '*.orig' -x '*.rej' -x '*.swp' 10.11-0/wx+/app_main.h 10.11-1/wx+/app_main.h
--- 10.11-0/wx+/app_main.h	2019-04-12 07:59:44.936143019 -0400
+++ 10.11-1/wx+/app_main.h	2019-04-12 10:19:57.228913439 -0400
@@ -7,6 +7,8 @@
 #ifndef APP_MAIN_H_08215601837818347575856
 #define APP_MAIN_H_08215601837818347575856
 
+#define __GXX_ABI_VERSION 1002
+
 #include <wx/window.h>
 #include <wx/app.h>
 
diff -Naur -x '*.orig' -x '*.rej' -x '*.swp' 10.11-0/zen/ring_buffer.h 10.11-1/zen/ring_buffer.h
--- 10.11-0/zen/ring_buffer.h	2019-04-12 07:59:46.098196548 -0400
+++ 10.11-1/zen/ring_buffer.h	2019-04-12 10:19:57.228913439 -0400
@@ -9,6 +9,7 @@
 
 #include <cassert>
 #include "scope_guard.h"
+#include <cstddef>
 
 
 namespace zen
diff -Naur -x '*.orig' -x '*.rej' -x '*.swp' 10.11-0/zen/serialize.h 10.19-1/zen/serialize.h
--- 10.11-0/zen/serialize.h	2019-04-12 07:59:46.080195719 -0400
+++ 10.19-1/zen/serialize.h	2019-12-27 11:35:50.379901321 -0500
@@ -10,6 +10,7 @@
 #include <functional>
 #include <cstdint>
 #include <stdexcept>
+#include <cstddef>
 #include "string_base.h"
 //keep header clean from specific stream implementations! (e.g.file_io.h)! used by abstract.h!
 
Message: For -std=c++17 we do not get to use charconv. It appears it is not actually in use, because the application compiles with this patch.
diff -Naur -x '*.orig' -x '.git*' -x '*.swp' -x '*.rej' 10.18-0/zen/legacy_compiler.cpp 10.18-1/zen/legacy_compiler.cpp
--- 10.18-0/zen/legacy_compiler.cpp	2019-11-21 20:59:02.633016149 -0500
+++ 10.18-1/zen/legacy_compiler.cpp	2019-11-21 20:59:31.042340308 -0500
@@ -5,7 +5,7 @@
 // *****************************************************************************
 
 #include "legacy_compiler.h"
-#include <charconv>
+//#include <charconv>
 //1. including this one in string_tools.h blows up VC++:
 //  "An internal error has occurred in the compiler. (compiler file 'd:\agent\_work\1\s\src\vctools\Compiler\Utc\src\p2\p2symtab.c', line 2618)"
 //2. using inside PCH: "fatal error C1076: compiler limit: internal heap limit reached"