Syntax bug R2011a: x ==y

12 次查看（过去 30 天）
Daniel Shub
Daniel Shub 2012-9-20
In coming up with an answer to another question I was playing around and think I found a bug in R2011a in Linux. Can anyone explain
>> x = randi(2, 10, 1)-1; % Dummy data
>> x == 0;
>> x ==0;
??? Error: "x" was previously used as a variable,
conflicting with its use here as the name of a function or command.
See MATLAB Programming, "How MATLAB Recognizes Function Calls That Use
Command Syntax" for details.
The 2nd and 3rd line differ in the presence (works) and absence (errors) of a space after ==. I cannot think of why the space matters. The error message also doesn't make sense to me. Is this reproducible? Is it a bug?
  3 个评论
显示 1更早的评论
Javier
Javier 2012-9-20
编辑：Javier 2012-9-20
Hello Tom
You have to give an additional space in the second x definition. No error in Matlab R2012a for Mac
>> x = randi(2, 10, 1)-1; % Dummy data
>> x == 0;
>> x == 0; %differs from x ==0; or
>> x=randi(2, 10, 1)-1; % Dummy data
>> x==0;
>> x==0;
Daniel Shub
Daniel Shub 2012-9-20
@Javier, but I am specifically asking about the odd case of x ==0 (with a space before, but not after, ==). I think of MATLAB as being generous about the usage of white space. This is a case where you need to follow a few rules.

请先登录，再进行评论。

请先登录，再回答此问题。

采纳的回答

Sean de Wolski
Sean de Wolski 2012-9-20
编辑：Sean de Wolski 2012-9-20
It is seeing ==0 as a string and x as a function. I.e. equivalent to:
x '==0';
This is not a bug. From the doc:
Space after an identifier, but not after a potential operator, implies a function call using command syntax. For example:
ls ./d
Reference
  4 个评论
显示 2更早的评论
Sean de Wolski
Sean de Wolski 2012-9-20
编辑：Sean de Wolski 2012-9-20
Hence it throws the error for the conflict (it wants to call x as a function but can't because it's a variable)
Also:
x('==0') is equivalent to >>x '==0' and apparently >>x ==0
Jan
Jan 2013-3-5
The different behavior between "x == 0" and "x ==0" might be a documented bug. The smartness of Matlab intelligent auto-parsing of the non-functional form exceeds the intuition of programmers. Now I'm unsure avour "x>0" and "x >=0" also.
The number of forum users struggeling with save(FileName) compared to save FileName decreases. I assume the newer documentation is better.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Desktop 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by