copy tick 函数经常无法取到tick；function “copy tick”sometimes cannot get tick

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CopyTicks(NULL,tickay,COPY_TICKS_TRADE,1,50);

这个函数经常无法取到tick，请问用法上有什么要注意的吗？成因可能是什么？

this function sometimes cannot get ticks， are there anything wrong with my usage？ What might be the cause？

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应该要先定义symbol，我一般选择COPY_TICKS_INFO，数据信息更多。如

CopyTicks("XAUUSD",tick_array,COPY_TICKS_INFO,0,ticks);