What is the significance of single quotes vs double quotes in comparisons?

Question

This returns an error:

return (arg[0] == "-" && arg[1] == "-") ? true : false;

error: ISO C++ forbids comparison between pointer and integer

However, this does not:

return (arg[0] == '-' && arg[1] == '-') ? true : false;

What is the difference between ' and " ?

score 22 · Accepted Answer · edited Jan 07 '12 at 06:26

22

Single-quotes denote a character literal. Double-quotes denote a string literal.

So '-' is of type char¹, whereas "-" is of type const char[2] (which typically decays to const char *).

_{1 int in C.}

edited Jan 07 '12 at 06:26

Martin York

answered Jan 07 '12 at 03:26

`'-'` is of type `char`. – James McNellis Jan 07 '12 at 03:28
@JamesMcNellis: Interesting, I didn't realised this differed between C++ and C. – Oliver Charlesworth Jan 07 '12 at 03:31
1

"An ordinary character lineral that contains a signle c-char has type **char**, with the value equal to the numerical value of the encoding of the c-char in the execution character set." (03 C++ standard) – Don Reba Jan 07 '12 at 03:33
Indeed. If it were a multicharacter literal (e.g. `'--'`), then it would be of type `int`. – James McNellis Jan 07 '12 at 03:51

1 Answers1