How to write binary data into a string or stringstream?

Asked Jan 04 '21 at 07:43

Active Jan 04 '21 at 07:46

Viewed 39 times

I want to write binary bytes (for example, 0xAA and 0xDD) into a stringstream.

const uint8_t sync_word_1 = 0xAA;
const uint8_t sync_word_2 = 0xDD;

std::stringstream ss;
ss.write((char*)&sync_word_1, sizeof(sync_word_1));
ss.write((char*)&sync_word_2, sizeof(sync_word_2));

// print for debug
for (int i = 0; i < ss.str().size(); i++) {
    printf("0x%02X ", ss.str()[i]);
}

What I expect:

0xAA 0xDD

What I got:

0xFFFFFFAA 0xFFFFFFDD

What did I miss?

edited Jan 04 '21 at 07:46

John Kugelman

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asked Jan 04 '21 at 07:43

Qiao

Try with `1` instead of `sizeof(sync_word_1)` – Basile Starynkevitch Jan 04 '21 at 07:46
@BasileStarynkevitch, nothing changed, thanks anyway. – Qiao Jan 04 '21 at 07:49
2

Your `printf` is wrong, you're printing an integer but passing a character – Alan Birtles Jan 04 '21 at 07:50
1

@Alan Yepp, agree: [**Demo on coliru**](http://coliru.stacked-crooked.com/a/dd27e500b4fd34ea) – Scheff's Cat Jan 04 '21 at 07:52
@Scheff, thank you! – Qiao Jan 04 '21 at 07:55
_What did I miss?_ `printf()` is a function using variadic arguments for the added values. These values are always subject of promotion. Hence, `char` is passed as `int`. To tell `printf()` that it was originally a `char`, you have to use "formatting modifier" - i.e. `%hhx` instead of `%x`. – Scheff's Cat Jan 04 '21 at 07:57
FYI: [Variadic arguments - Default conversions](https://en.cppreference.com/w/cpp/language/variadic_arguments#Default_conversions) – Scheff's Cat Jan 04 '21 at 07:59

How to write binary data into a string or stringstream?

0 Answers0