Is it true that using pointers is significantly faster than using array syntax in C?

Question

With current C compilers, is it true that using array syntax (a [i]) is slower than using pointers (* (p + i))?

Answer 1

They must be the same. But:

for( i = 0; i < ...; ++ i ) ... array[i] ...

may be slower than:

for( p = array; *p; ++ p ) ... *p ...

because in the first case, the compiler may be needed *(array+i), and in the second you are simple (*p).

In trivial cases, however, the compiler must be able to optimize and generate the same machine code.

Answer 2

. - .

Answer 3

, C ++ a[i] *(a+i). , a[1] 1[a]. :)

Answer 4

! a[i] *(a+i).

a[i] = *(a + i) = *(i + a) =i[a];

Answer 5

x86 x86_64 p[i] *(p+i) ( : C) , p , , i - . x86 /, , 2.

, i p, , , . x86:

• a (static extern global) , PIC, a[i] *p ( i) (, 0xdeadbeef(,%ecx,4) vs (%esi)).
• a ( ), , a[i] *p (, 12(%esp,%ecx,4) vs (%esi) %esp, ).
• a PIC, a[i], , , *p, i .
• a , , a[i] , *p (, (%eax,%ecx,4) vs (%esi)).

Answer 6

, -

while (*s++ = *d++)
   ;

,

while (s[i] = d[i])
   i++;

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Answer 7

, .

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Answer 8

. , ,

int a[];
for (int n = 0; n < size; n++) { ... Do stuff with a[n]; }

a,

int a[size];
int *end = a + size;
for (int *i = a; i != end; ++i) { ... Do the same stuff with *i ; }

, .

Answer 9

, , , .

// which is faster? *t or t[i]?
process_some_array(T *t, size_t n)
{
    T *end = &t[n];
    for (T *t = t; t < end; ++t)
        // do stuff with *t
    for (size_t i = 0; i < n; ++i)
        // do stuff with t[i]
}

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Answer 10

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