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Re: array indexing vs pointer arithmetic

Nov 9th, 2008

From the C++ Standard:

•

The expression E1[E2] is identical (by definition) to *((E1)+(E2)).

Sometime pointer arithmetics code is evidently cleaner than "subsripted" one:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int countDigits(const char* str)
{
    int n = 0;
    if (str)
    while (int c = *str++)
        if (c >= '0' && c <= '9')
            ++n;
    return n;
}
int countDigits(const char* str)
{
    int n = 0;
    if (str)
    while (int c = *str++)
        if (c >= '0' && c <= '9')
            ++n;
    return n;
}

Sometimes we have no choice: as usually (but not always) pointer arithmetics code is faster than "subscripted" one on embedded systems where we (often) must save on every microsecond...

It's a far-fetched problem. It's not a language problem...