When comparing characters, is ischar(x) && x == 'b' equivalent to strcmp(x, 'b')?

Question

In MATLAB, I often use this to check if a variable contains a certain single character:

if ischar(x) && x == 'b'

to reduce clutter I'm thinking of changing it to this:

if strcmp(x, 'b')

because if x isn't a character or isn't equivalent to 'b', the comparison returns false as you would expect. Are these statements equivalent in this case or are there gotchas?

More info: x == 'b' isn't enough because this returns true when x == 98, but in certain cases (like validating user input), 98 may be invalid input while b is valid input. Also, the first one fails if x isn't a standard data type (if it's an object for example). Take this (stupid) example:

x = table();
x == 'b'

This throws an error because eq isn't defined for tables, but strcmp(x, 'b') returns 0 because it appears that strcmp also performs a type check. Whether or not this exception handling is desirable probably depends on the circumstances though.

Answer 1

strcmp is the way to go. The == operator is element-wise. If x is not a single character, then the test returns a logical array instead of one:

>> x = 'abc';
>> x == 'b'
ans =
     0     1     0
>> x = 'bbb';
>> x == 'b'
ans =
     1     1     1

Neither are equal, the second one satisfies the if statement.

Also note that while == (eq) is element-wise, isequal tests for object equality. The caveat is that isequal does not consider data type in the test. That is:

>> isequal('abc',[97 98 99])
ans =
     1
>> strcmp('abc',[97 98 99])
ans =
     0
>> eq('abc',[97 98 99])
ans =
     1     1     1

If you care about data type, use strcmp, if not, use isequal.

Consider also using strcmpi to ignore case or strncmp to compare the first N elements.