There're a lot of questions on SO about details of pointer and array declarations in C (and C subset of C++).
I'm more interested in why.
Why do we have to put *
, []
in front of every variable when we declare several pointers/arrays in a row?
int *a, *b;
int c[1], d[1];
Why do we have to type out things after/around variable names in function pointers?
void (*foo_ptr)(int, int);
Why do we have this feature that confuses a lot of newcomers, when even compilers recognize and report these things as part of type? Ex: function foo accepts int** but it was given int*
I guess I'm looking for intuition behind it that caused it being created this way, so that I can apply it to my understanding of the language. Right now I just don't see it...
Kernighan and Ritchie write, in The C Programming Language, 1978, page 90:
The declaration of the pointer
px
is new.
int *px;
is intended as a mnemonic; it says the combination
*px
is anint
, that is, ifpx
occurs in the context*px
, it is equivalent to a variable of the typeint
. In effect, the syntax of the declaration for a variable mimics the syntax of expressions in which the variable might appear. This reasoning is useful in all cases involving complicated declarations. For example,
double atof(), *dp;
says that in an expression
atof()
and*dp
have values of typedouble
.
Thus, we see that, in declarations such as int X, Y, Z
, X
, Y
, and Z
give us “pictures” of expressions, such as b
, *b
, b[10]
, *b[10]
, and so on. The actual type for the declared identifier is derived from the picture: Since *b[10]
is an int
, then b[10]
is a pointer to an int
, so b
is an array of 10 pointers to int
.