Can't get fullPath in IOS

std::string fullPath = CCFileUtils::sharedFileUtils()->fullPathForFilename(“config/g”);
with coding like this, the value of fullPath is “config/g”,
std::string fullPath = CCFileUtils::sharedFileUtils()->fullPathForFilename(“g”);
this value of fullPath is “…app\g”, got the fullPath

why?

no problem in Android,but in iOS i always can’t get the fullPath
such as
CCSprite::create(“UI/star.png”); //can’t load the data;

thanks for help