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2.1.21 -E選項：只進行預處理
NASM允許在一定條件下，單獨進行預處理操作。-E選項（沒有參數）會使NASM只進行預處理操作，即展開所有的宏，移除所有的註釋和預處理指令。並且將預處理結果輸出到標準輸出中，或者是-o選項指定的文件中。
如果源代碼中使用了預處理求值表達式，且表達式的值依賴sysmbols,使用-E時NASM會報錯。如下：
%assign tablesize ($-tablestart)
爲了兼容舊版的NASM，也可以使用小寫的-e。在舊版中-E的作用等同於目前的-Z，參見2.1.15。
2.1.21 -a選項：始終不進行預處理
如果將NASM用作某個編譯的後端，如果編譯器已經完成了所有預處理操作。此時爲了節約時間加快編譯速度，需要完全禁止NASM的預處理。-a選項使NASM不做任何預處理操作。