C++ string function return statement

Question

I'm trying to add int to string in a return statement like so:

string Birthday::asString() {
    return this -> day + "/" + this -> month + "/" + this -> year;
}

and getting the following error:

Error: expression must have integral or unscoped enum type

I'm kind of new to C++.

sscce.org. Or, in other words: Neither "string" nor "Birthday" nor "this" nor "day" nor "month" nor "year" are actually defined in the code snippet you have posted. — DevSolar
– DevSolar, Commented Apr 25, 2013 at 12:28
Also, this is the first time I saw anyone putting spaces between operands of ->. — milleniumbug
– milleniumbug, Commented Apr 25, 2013 at 13:55

Ivaylo Strandjev · Accepted Answer · 2013-04-25 12:35:24Z

11

Easiest way to do what you are trying to do is to use ostringstream(found in header <sstream>):

string Birthday::asString() {
    std::ostringstream out;
    out << this -> day << "/" << this -> month << "/" << this -> year;
    return out.str();
}

You are getting the error you show because C++ does not know how to add an integer to a string.

EDIT: as suggest in M M.'s answer since C++11 there is another option, namely to use the function std::to_string.

edited Apr 25, 2013 at 12:35

answered Apr 25, 2013 at 12:28

Ivaylo Strandjev

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7 Comments

user1970719 Over a year ago

Is there a way for doing this without creating an object ? I think that is a better practice

Ivaylo Strandjev Over a year ago

@user1970719 you need to convert the integers to strings so you will need to create a new object.

Andrew Tomazos Over a year ago

@user1970719: The object being the ostringstream instance? Actually the ostringstream solution is superior in terms of performance than the std::to_string solution.

syam Over a year ago

No, the easiest way is to use std::to_string. Yes it is C++11, but this is the current standard (and thus the default) so you should probably mention that your solution is for the older C++03.

Ivaylo Strandjev Over a year ago

@syam though I agree I must mention this alternative(and I already did in an edit) I still think what I suggest is a bit easier to both read and write in this case.

|

masoud · Accepted Answer · 2013-04-25 12:38:44Z

7

You can use std::to_string:

string Birthday::asString() {
     return std::to_string(this->day) + "/" +
            std::to_string(this->month) + "/" +
            std::to_string(this->year);
}

Available since C++11

edited Apr 25, 2013 at 12:38

answered Apr 25, 2013 at 12:29

masoud

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1 Comment

alexrider Over a year ago

It is also available in not yet c++11 MSVC10 It lacks some C++11 overloads thru and may require some casts.

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