C++ - Efficient way to change endianness of arbitrary string

Asked Apr 20 '18 at 13:46

Active Apr 20 '18 at 14:36

Viewed 96 times

I want to change the endianness of arbitrary C++ string (std::string)

Ex : 01234567 change to 32107654. I do this

char *bswap32(const char *src) 
{
    char *dest = (char *)malloc(sizeof(char) * strlen(src));
    int idx = 0;
    while (idx < strlen(src)) {
        for (int i = 0; i<4; i++) {
            dest[i + idx] = src[idx + 3 - i];
        }
        idx += 4;
    }
    return dest;
}

And call like this

char *swapped = bswap32("01234567");
std::cout << swapped << std::endl;

But I'm not sure, is it the efficient way in C++ .....

Updated with use of std::string

std::string Sbswap32(const std::string src) 
{
    std::string dest (src.length(), ' ');
    size_t idx = 0;
    while (idx < src.length()) {
        for (int i = 0; i<4; i++) {
            dest.insert(i + idx, 1, src[idx + 3 - i]);
        }
        idx += 4;
    }
    return dest;
}

std::string sTest = "01234567";
std::string Sswapped = Sbswap32(sTest _8);
std::cout << Sswapped << std::endl;

edited Apr 20 '18 at 14:36

asked Apr 20 '18 at 13:46

LeMoussel

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4

Have you looked into `std::rotate`? – NathanOliver Apr 20 '18 at 13:48
8

But strings don't have endianness? What you're trying to do has no meaning. – Some programmer dude Apr 20 '18 at 13:48
3

Why `malloc` instead of using decent C++ features? – Fred Larson Apr 20 '18 at 13:49
2

@FredLarson Not to mention the UB that comes by using an unterminated C-style string. – Some programmer dude Apr 20 '18 at 13:49
1

@FredLarson Though I agree the design decision is questionable, strictly speaking there isn't a memory leak. It's still possible to `free` the allocation with `char *swapped`. – François Andrieux Apr 20 '18 at 13:50
@FredLarson I start in C ++ – LeMoussel Apr 20 '18 at 13:50
2

What should happen if `strlen(src) % 8 != 0`? Also `strlen` should be called only once, and certainly not in a loop. – Dialecticus Apr 20 '18 at 13:51
5

What's a string's endianness? – Ron Apr 20 '18 at 13:51
You state in your first sentence that you want to use `std::string` but your code is not using it. – DodgyCodeException Apr 20 '18 at 13:53
2

If I were to make a guess, I'd say that this is an academic exercise OP was given that tries to somehow "simulate" byte ordering modification using string manipulation functions. OP can confirm that this might be simply a 4-tuple-wise reversal that is not actually related to endianness. – SirDarius Apr 20 '18 at 13:55
If you're just starting in C++, then please [get a few good books](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list/388282#388282) and learn it properly. – Some programmer dude Apr 20 '18 at 13:56
@NathanOliver you mean `std::reverse` – Raymond Chen Apr 20 '18 at 14:05
@RaymondChen Yes, yes I did ;) good catch – NathanOliver Apr 20 '18 at 14:10
@ALL Upadte with with use of `std::string` – LeMoussel Apr 20 '18 at 14:37

C++ - Efficient way to change endianness of arbitrary string

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