與NASM彙編中使用％SUBSTR

Question

我複製粘貼在NASM文檔PDF頁面46下面的代碼：

`%substr` requires string as second parameter 

但atfer：

%substr mychar ’xyzw’ 1 ; equivalent to %define mychar ’x’ 

而且組裝它，我收到以下錯誤後我把'xyzw'改爲'xyzw'或者'xyzw'，它的效果很好。那麼我在這裏錯過了什麼？

Answer 1

正確的語法示於online documentation

%substr mychar 'xyzw' 1  ; equivalent to %define mychar 'x' 

一般地，對於它談論字符串和字符串文字，其被解釋here，並且可以通過單引號包圍，雙引號和反引號預處理器字符串函數：

String constants are character strings used in the context of some pseudo-instructions, namely the DB family and INCBIN (where it represents a filename.) They are also used in certain preprocessor directives.

A string constant looks like a character constant, only longer.

而關於character constants（其中分隔符實際上解釋）：

A character string consists of up to eight characters enclosed in either single quotes ('...'), double quotes ("...") or backquotes (`...`). Single or double quotes are equivalent to NASM (except of course that surrounding the constant with single quotes allows double quotes to appear within it and vice versa); the contents of those are represented verbatim. Strings enclosed in backquotes support C-style -escapes for special characters.

至於說在註釋中，最有可能的PDF是由文字處理器急於排版漂亮的字符，而不是正確的人搞砸了。