关于逻辑操作符|,&与||,&&的区别

zhouyang664

    在进行逻辑操作时，符号|，&在遇到空矩阵时均返回[]，如下：
>> 4|[]  %只要操作数有[]，就返回[]
ans =
     []
>> 4&[]
ans =
     []
>> 1|[]
ans =
     []
>> 0&[]
ans =
     []
   而符号||，&&则在第一个条件满足时就返回判断结果，不再判断第二个条件，如下：
>> 4||[]  %4为真，直接返回1
ans =
     1
>> 0&&[] %0为假，直接返回0
ans =
     0
   但||，&&似乎不支持[]作为有效操作数，如下：
>> 0||[] % 根据0，不能判断操作结果，执行第二个操作数，出错：
??? Operands to the || and && operators must be convertible to logical scalar
values.
>> 1&&[] % 根据1，不能判断操作结果，执行第二个操作数，出错：
??? Operands to the || and && operators must be convertible to logical scalar
values.

    但在if语句中 |，&和||，&&的行为就相同了：
if 4 | []
    disp('Must be true')
end
Must be true
if 4 || []
    disp('Must be true')
end
Must be true
   官方文件称||，&&的这种行为为short-circuit，常用于if和while语句中！

欢迎大家一起探讨！

qibbxxt

按照help中的解释，区别是

1. Note the difference between the elementwise and short-circuit logical operators. Short-circuit operators, such as && and ||, test only as much of the input expression as necessary. In the second part of this example, it makes no difference that B is undefined because the state of A alone determines that the expression is false:
   
2. 
   
3. A = 0;
   
4. A & B
   
5. ??? Undefined function or variable 'B'.
   
6. 
   
7. A && B
   
8. ans =
   
9.      0

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当然，还有

1. 
   
2. &   Element-wise Logical AND.
   
3.       A & B is a matrix whose elements are logical 1 (TRUE) where both A
   
4.       and B have non-zero elements, and logical 0 (FALSE) where either has
   
5.       a zero element. A and B must have the same dimensions (or one can
   
6.       be a scalar).
   
7. && Short-Circuit Logical AND.
   
8.       A && B is a scalar value that is the logical AND of scalar A and B.
   
9.       This is a "short-circuit" operation in that MATLAB evaluates B only
   
10.       if the result is not fully determined by A. For example, if A equals
    
11.       0, then the entire expression evaluates to logical 0 (FALSE), regard-
    
12.       less of the value of B. Under these circumstances, there is no need
    
13.       to evaluate B because the result is already known.

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当然在实际运用过程中，需要达到自己的效果是，如果用&不行，就用&&，反正也不多，试一试呗

zhouyang664

好，学习学习！

ChaChing

0||[]及1&&[], 不支持[]作为有效操作数
新学到, 谢谢分享!