Quick-x 文件读写

Cocos2d-x Lua
#1 
function writelog(content)
    if (Launcher.platform == "android" or Launcher.platform == "ios") then
        local path = CCFileUtils:sharedFileUtils():getWritablePath()
        local fileName = path.. "debug.log"
        
        local newContent = ""..(os.time{year=2010, month=1, day=1, hour=0,min=1, sec=1}).."] "..content.."\n"
        local mode = "a"
       
        local file = io.open(fileName, mode)
        if file then
            if file:write(newContent) == nil then 
                print('write failed '..newContent)
            end
            io.close(file)
        else
            print('open log failed')
        end
    end
end

想做个真机的log，在ios上没有问题，android上无法创建文件，哪位大哥知道什么问题?

#2

mode好象应该是"a+"？另外看一下有没有写权限