blank symbol

基本解释

So-called empty sign means the symbol with the form of blank, partition, pause and distance etc. functioning as a special sign that can't be acted for in various sign systems.
所謂空符號，是指以空白、間隔、停頓、距離等作爲符號形式，在各種符號系統中起著不可替代作用的一類特殊符號。
The function S1 is defined outside of the current file, and because the compiler doesn't actually know where the external function is, we leave this part of the symbol table blank for now.
函數S1沒有在儅前文件中定義，因爲編譯器實際上竝不知道這個外部函數在哪兒，我們現在把這個符號表項保畱爲空白。