A CPP int to string in a statement question

Question

I have to write something like

q.push_back(q1); ... to ... q.push_back(q100);

I am writing this as

for (int i = 1; i <= 100; i++) {
    try {
        std::string s = boost::lexical_cast<std::string > (i);
        "q.push_back(q" + s + ");";
    } catch (boost::bad_lexical_cast &) {
        std::cout << "Some error message \n";
    }
}

It compiles (no syntax errors) but does not work. I don't know how to mix cpp statements and strings to make a compound statement.

Any help here would be highly appreciated. Thanks!

It works perfectly. I just doesn't do what you want it to, but that's an entirely different matter. But to make sure I'm not misunderstanding you: You have a hundred variables q1, q2, q3, ... q100 and you want to put them into one vector, right? — user395760
– user395760, Commented Sep 19, 2011 at 15:44
"q.push_back(q" + s + ");"; what did you expect this string literal to do? — AJG85
– AJG85, Commented Sep 19, 2011 at 16:02
Yes I want a shortcut way to write q.push_back(q1); .. to q.push_back(q100); in the code. — Ayesha Kalra
– Ayesha Kalra, Commented Sep 19, 2011 at 16:03
@AJG85 - I kind of knew this would not work as this is just a string literal and not a statement. — Ayesha Kalra
– Ayesha Kalra, Commented Sep 19, 2011 at 16:06
@Ayesha You'll probably need a macro if you want to generate the code that does this. — AJG85
– AJG85, Commented Sep 19, 2011 at 16:08

Oliver Charlesworth · Accepted Answer · 2011-09-19 15:44:13Z

1

How about:

for (int i = 1; i <= 100; i++)
{
    std::cout << "q.push_back(q" << i << ");\n";
}

answered Sep 19, 2011 at 15:44

Oliver Charlesworth

274k34 gold badges591 silver badges687 bronze badges

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

Comments

RageD · Accepted Answer · 2011-09-19 15:44:31Z

0

If you're using std::string (which it looks like you are) try s.append(str);

answered Sep 19, 2011 at 15:44

RageD

6,8434 gold badges32 silver badges37 bronze badges

Comments

Cătălin Pitiș · Accepted Answer · 2011-09-19 15:49:07Z

0

std::ostringstream os;
for( int i = 1; i < 100; ++i)
{
   os << "s.push_back( q" << i << "); ";
}
std::string result = os.str();
// Do what you need with result

Your output string was put inside the for loop, so at each loop the string is initialized, the content generated in the previous loop was lost.

answered Sep 19, 2011 at 15:49

Cătălin Pitiș

14.4k2 gold badges41 silver badges63 bronze badges

Comments

Tom Kerr · Accepted Answer · 2011-09-19 15:50:38Z

0

You aren't telling it where to put that string, it just creates a temporary. Try appending to s.

std::string s = "q.push_back(q";
s.append(boost::lexical_cast<std::string > (i));
s.append(");");

It isn't clear what you expect to do with the string. If you are printing it to std::cout, then your error message will get mixed in with the results. You should use std::cerr instead.

std::cerr << "Some error message" << std::endl;

edited Sep 19, 2011 at 15:50

answered Sep 19, 2011 at 15:44

Tom Kerr

10.8k2 gold badges33 silver badges46 bronze badges

Comments

Keith Thompson · Accepted Answer · 2011-09-19 16:13:07Z

0

The variables q1, q2, ..., q100 should have been an array in the first place.

answered Sep 19, 2011 at 16:13

Keith Thompson

266k46 gold badges447 silver badges668 bronze badges

Comments

Bogdan Matican · Accepted Answer · 2011-09-20 09:28:27Z

0

If my understanding of what you are trying to do is correct, then you basically want to automatically generate some code. For that, people normally use simple macro definitions...

You can just define a macro that takes your respective integer from the for loop as a parameter and expands to the code you require with it...

Take a quick look at [ http://en.wikipedia.org/wiki/C_preprocessor#Token_concatenation ]. You can use ## in macros to glue things together, so you could use something like the following, inside a for loop for i:

#define MY_PUSH(vector, i) vector.push_back(q##i);

But as people have suggested, it might have been better to use an array of variables in the first place, as macros are basically evil for anything other than raw code generation tools...

edited Sep 20, 2011 at 9:28

answered Sep 19, 2011 at 15:49

Bogdan Matican

295 bronze badges

3 Comments

Ayesha Kalra Over a year ago

This is exactly what I want, could you provide an example please? Thanks!

Ayesha Kalra Over a year ago

I haven't used a Macro before.

Bogdan Matican Over a year ago

and you should aim at never using them, especially in a C++ environment, as they can get you in a lot more trouble than they can get you out...

Collectives™ on Stack Overflow

A CPP int to string in a statement question

6 Answers 6

Comments

Comments

Comments

Comments

Comments

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

Comments

Comments

Comments

Comments

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related