Proxy checking

[pizzaman66621]

Hi Im working on a C++ checker. Well as of right now Im just testing certain parts out like multi threading and some other shit but I was wondering how would someone check if a proxy is working or not. I do know that sometimes some proxies are presumed as dead but then 5 minutes later they are working. I just dont know how to make a simple proxy checker? Do I like use some type of web api or like setup a socket? 

Thanks