char array string confusion

Question

I'm in trouble and I cannot wrap my head around this myself..

// string::operator+= vs +
#include <iostream>
#include <string>
using namespace std;


int main ()
{
    unsigned char array[6]= { 'f','o','o','b','a','r' };
    string name ("works and not");
    cout << name<< endl;
    name ="";
    for(int i=0; i < 6;  i++)
        name += array[i];
    cout << "working: "<< name << endl;
    name ="";
    name = array[1] + array[0] + array[0] + array[3] + array[4] + array[5]; 
    cout <<"not working: "<<  name << endl;
    return 0;
}

Now I understand that there's some hidden conversion going on in += notation, and I get, that the plus symbol adds the integers of my characters, and just converts the final value (to 'p').

But I need to combine various chars into one string.. in one line if possible.. since I need to do that more than once (600++ times) and it's already messing the code up.

since this is the first, and most likely last time I need to convert my "array" values to a string, I'd rather NOT change my char array btw.

thank you!

"I need to do that more than once (600++ times)" Huge code smell here. — Lightness Races in Orbit
– Lightness Races in Orbit, Commented Mar 1, 2015 at 18:34

Lightness Races in Orbit · Accepted Answer · 2015-03-01 18:42:35Z

2

name = array[1] + array[0] + array[0] + array[3] + array[4] + array[5];

The requirement to do this all in one line is your problem. The right-hand side of the = is evaluated before the fact that name is even considered. And, yes, since those are all unsigned chars, all you're getting is unsigned char addition.

If your array were of char, there'd be a shortcut:

name = std::string() + array[1] + array[0] + array[0] + array[3] + array[4] + array[5];

Now the RHS is being built up from a series of operator+ as applied to a (temporary) std::string, and the final concatenated result copy-assigned into name. It's pretty ugly but...

But you can't use this with your unsigned chars, because there is no operator+ for std::string and unsigned char. You've basically designed yourself into a corner so, if you can't use loops or use a std::string to start with in the first place, you're SOL.

If you don't mind a bit of refactoring, though, here's a 2015 solution:

#include <iostream>
#include <string>

int main()
{
    unsigned char array[6] = { 'f','o','o','b','a','r' };
    std::string name;

    for (auto i : {1,0,0,3,4,5})
        name += array[i];

    std::cout << name << '\n';
}

(live demo)

edited Mar 1, 2015 at 18:42

answered Mar 1, 2015 at 18:32

Lightness Races in Orbit

387k77 gold badges670 silver badges1.1k bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

itsid Over a year ago

Oh.. it's soo easy sometimes, isn't it's not actually too difficult to use signed chars for me, one more line of code.. no big deal, but that didn't came to my mind AT ALL! So thanks a million!!!!

Lightness Races in Orbit Over a year ago

@itsid: No problem. As a bonus, I've put a proper, modern solution into my answer.

itsid Over a year ago

Oh I like the 2015 solution! ... hmm.. time to step up I guess :D

Collectives™ on Stack Overflow

char array string confusion

1 Answer 1

(live demo)

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

(live demo)

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related