My mobile phone suddenly shows that there is not enough memory, so I can't receive any short messages. I don't know what happened.

Your mobile phone may be an Android phone at that time, and the storage space is relatively small (less than 4 GB), so it is easy to be full. My dad's mobile phone is like this. In this case, you need to try not to install useless applications, and try to put applications and personal data in external storage (usually SD card). You said that your mobile phone memory (strictly speaking, the storage space of the mobile phone itself) was already a lot, but later it was not enough, and it was useless to delete the application. If this happens, I will use 360 to clean up first, because sometimes the garbage generated by the application installation, uninstallation and transfer cannot be cleaned up in time. Then, if it is not solved, you can try to transfer all the software installed in the mobile phone to the SD card, but I need to tell you that according to experience, even the applications in the SD card occupy the mobile phone's own storage more or less, so try to delete useless applications. Next, you can try to delete the program installation package, application cache, useless personal files, useless mobile phone software (you need to crack ROOT permissions), or restart. These should be all right. It is more troublesome to restore the factory settings, because everything will be erased, so personal data should be backed up, then reset and download the software again ... so I don't recommend it unless it is absolutely necessary.