How does GetLastError() work ?

[ffoorr]

Does the last error remain in the  GetLastError() fonction until a new error come

Or does the   GetLastError() fonction is reset ?

[Keith Watford]

Does the last error remain in the  GetLastError() fonction until a new error come

Yes 

Or does the   GetLastError() fonction is reset ?

No, unless you reset it with ResetLastError()

Usually , when calling a function, you can check the return value to see if there was an error or not. If there was an error call GetLastError() 

[ffoorr]

Thank's

[honest_knave]

From GetLastError():

"After the function call, the contents of _LastError are reset."

[William Roeder]

honest_knave: From GetLastError(): "After the function call, the contents of _LastError are reset."

And that used to be true before Build 600. Then the documentation said ResetLastError - MQL4 Documentation (29 Jul 2014) Note It should be noted that the GetLastError() function doesn't zero the _LastError variable. Usually the ResetLastError() function is called before calling a function, after which an error appearance is checked. And now it says Note The GetLastError() function  zero the _LastError variable.