Function ImFileGetSize

imgui_tiny_app/imgui/imgui.cpp:2592–2592

// We should in theory be using fseeko()/ftello() with off_t and _fseeki64()/_ftelli64() with __int64, waiting for the PR that does that in a very portable pre-C++11 zero-warnings way.
bool    ImFileClose(ImFileHandle f)     { return fclose(f) == 0; }
ImU64   ImFileGetSize(ImFileHandle f)   { long off = 0, sz = 0; return ((off = ftell(f)) != -1 && !fseek(f, 0, SEEK_END) && (sz = ftell(f)) != -1 && !fseek(f, off, SEEK_SET)) ? (ImU64)sz : (ImU64)-1; }
ImU64   ImFileRead(void* data, ImU64 sz, ImU64 count, ImFileHandle f)           { return fread(data, (size_t)sz, (size_t)count, f); }
ImU64   ImFileWrite(const void* data, ImU64 sz, ImU64 count, ImFileHandle f)    { return fwrite(data, (size_t)sz, (size_t)count, f); }
#endif // #ifndef IMGUI_DISABLE_DEFAULT_FILE_FUNCTIONS