PHP a set of programs how to properly structure the PC-side and mobile Web site automatically switch access to it

Program for the same set, the domain name structure is as follows:
PC-side domain name: www.xxxx.com mobile domain: m.xxxx.com
How to reasonably build the PC end and mobile phone end automatically switch access,
Don't tell me that when I visit my phone I add a function to judge,
In addition to the template is not the same, the terminal should be more reasonable to control

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Program for the same set, the domain name structure is as follows:
PC-side domain name: www.xxxx.com mobile domain: m.xxxx.com
How to reasonably build the PC end and mobile phone end automatically switch access,
Don't tell me that when I visit my phone I add a function to judge,
In addition to the template is not the same, the terminal should be more reasonable to control

The server can be exactly the same ... Render the function of the page to distinguish the front-end template on it

Responsive layout?

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