Berkeley CSUA MOTD:Entry 32241
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2025/05/24 [General] UID:1000 Activity:popular
5/24    

2004/7/12-13 [Computer/SW/Languages/C_Cplusplus] UID:32241 Activity:very high
7/12    In C, what should be the data type for array indices?  I usually just
        use "int".  Thx.
        \_ YES!  The 'trivial C question troll' is back!  I love you, man!
        \_ int is fine, but I often find myself using unsigned int, especially
           in for loops where I compare unsigned int i against some maximum-
           value variable that is also unsigned int.
        \_ It's an integer type.  a[i] is the same as *(a + i).  Can be signed,
           can be negative.  Why do you care?
           \_ I'm just wonder if the K&R spec says anything about it.  I don't
              have the spec here.
        \_ size_t
           \_ Are you sure?  It's not, say, ptrdiff_t?  Isn't a[-1] legal?
                \_ You can use ssize_t if you like, I personally prefer
                   size_t since stuff like a[-1] can often lead to bugs
                   if you aren't completely sure what a points to.
                   \_ The original question wasn't what type /should/ be
                      used; it was what it *is*.  Section 6.5.2.1 of the
                      C99 standard says merely, "integer type" and (as I
                      said before) that a[i] is identical to *(a + i) (from
                      which it should be obvious that the index is an integer
                      type).
        \_ To settle this question once and for all, just look at the C
           standard? It says the subscript shall be an integral type.
           Integral type is defined as char, an unsigned or signed integer
           type, or an enumerated type. A signed integer type is signed
           char, short int, int, or long int, and unsigned integer type is
           the corresponding unsigned type. Clear enough?
           \_ You could have just said:  The C standard (post URL) says the
              index can be an integral type (signed/unsigned short/long
              char, int, enum), and negative values are permitted.
              \_ There is no URL for the C standard. Or not a legal one,
                 anyway. There are various draft standards, though.
           \_ what about long long?
              \_ above is for C90. C99 draft standard has somewhat different
                 verbiage, but the spirit is the same. basically all integer
                 types can be subscripts.
2025/05/24 [General] UID:1000 Activity:popular
5/24    

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