Added IMGUI_DISABLE_FORMAT_STRING_FUNCTIONS support in imconfig.h (#1038)

imconfig.h

@@ -13,6 +13,9 @@
 //#define IMGUI_API __declspec( dllexport )
 //#define IMGUI_API __declspec( dllimport )
 
+//---- Don't define obsolete functions names. Consider enabling from time to time or when updating to reduce like hood of using already obsolete function/names
+//#define IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+
 //---- Include imgui_user.h at the end of imgui.h
 //#define IMGUI_INCLUDE_IMGUI_USER_H
 
@@ -24,13 +27,13 @@
 //---- It is very strongly recommended to NOT disable the test windows. Please read the comment at the top of imgui_demo.cpp to learn why.
 //#define IMGUI_DISABLE_TEST_WINDOWS
 
-//---- Don't define obsolete functions names. Consider enabling from time to time or when updating to reduce like hood of using already obsolete function/names
-//#define IMGUI_DISABLE_OBSOLETE_FUNCTIONS
+//---- Don't implement ImFormatString(), ImFormatStringV() so you can reimplement them yourself.
+//#define IMGUI_DISABLE_FORMAT_STRING_FUNCTIONS
 
 //---- Pack colors to BGRA instead of RGBA (remove need to post process vertex buffer in back ends)
 //#define IMGUI_USE_BGRA_PACKED_COLOR
 
-//---- Implement STB libraries in a namespace to avoid conflicts
+//---- Implement STB libraries in a namespace to avoid linkage conflicts
 //#define IMGUI_STB_NAMESPACE     ImGuiStb
 
 //---- Define constructor and implicit cast operators to convert back<>forth from your math types and ImVec2/ImVec4.

imgui.cpp

@@ -1011,6 +1011,7 @@ static const char* ImAtoi(const char* src, int* output)
 
 // MSVC version appears to return -1 on overflow, whereas glibc appears to return total count (which may be >= buf_size). 
 // Ideally we would test for only one of those limits at runtime depending on the behavior the vsnprintf(), but trying to deduct it at compile time sounds like a pandora can of worm.
+#ifndef IMGUI_DISABLE_FORMAT_STRING_FUNCTIONS
 int ImFormatString(char* buf, int buf_size, const char* fmt, ...)
 {
     IM_ASSERT(buf_size > 0);
@@ -1033,6 +1034,7 @@ int ImFormatStringV(char* buf, int buf_size, const char* fmt, va_list args)
     buf[w] = 0;
     return w;
 }
+#endif // #ifdef IMGUI_DISABLE_FORMAT_STRING_FUNCTIONS
 
 // Pass data_size==0 for zero-terminated strings
 // FIXME-OPT: Replace with e.g. FNV1a hash? CRC32 pretty much randomly access 1KB. Need to do proper measurements.