std::string and integers

**Tim Love** · Jul 22 '05, 04:01 PM

Re: std::string and integers

"Glen Able" <smeREMOVEckler s@hotMEmail.com > writes:
[color=blue]
>Obviously the following doesn't work:[/color]
[color=blue]
>int i = 5;
>std::string myString = "Number is " + i + " thankyou please";[/color]
[color=blue]
>So can anyone give me some idea what's the nicest way to this sort of thing?
>I'm sure it's not using sprintf.[/color]

You can use cout-style formatting to print to a string. See the FAQ

Miscellaneous technical issues, C++ FAQ

http://www.parashift.com/c++-faq-lite/misc-technical-issues.html#faq-38.1

**Gwar** · Jul 22 '05, 04:01 PM

Re: std::string and integers

On Thu, 8 Jul 2004, Glen Able wrote:
[color=blue]
> Obviously the following doesn't work:
>
> int i = 5;
> std::string myString = "Number is " + i + " thankyou please";
>
> So can anyone give me some idea what's the nicest way to this sort of thing?
> I'm sure it's not using sprintf.
>
> with thanks,
> G.A.
>
>
>[/color]
// one way:

#include <sstream>
#include <string>
#include <iostream>

using namespace std;

int main()
{
int i = 5;
string myString1 = "The number is ";
string myString2 = " thank you, please";

ostringstream os;

os << myString1 << i << myString2;
string msgString = os.str();

cout << msgString << endl;

}

**Anders Persson** · Jul 22 '05, 04:02 PM

Re: std::string and integers

try
int i = 5;
std::string myString;
myString = "Number is " + i + " thankyou please";
// ANders

On Thu, 08 Jul 2004 09:28:58 +0100, Glen Able wrote:
[color=blue]
> Obviously the following doesn't work:
>
> int i = 5;
> std::string myString = "Number is " + i + " thankyou please";
>
> So can anyone give me some idea what's the nicest way to this sort of thing?
> I'm sure it's not using sprintf.
>
> with thanks,
> G.A.[/color]

**Rolf Magnus** · Jul 22 '05, 04:02 PM

Re: std::string and integers

Anders Persson wrote:
[color=blue]
> try
> int i = 5;
> std::string myString;
> myString = "Number is " + i + " thankyou please";
> // ANders[/color]

This won't compile, since it's illegal in C++ to add two pointers
together.

myString = "Number is " + i;

would compile, but it would for sure not do what was intended.

**Glen Able** · Jul 22 '05, 04:02 PM

Re: std::string and integers

"Gwar" <xeno@xor.qua > wrote in message
news:2004070801 4542.U17241@syn ergy.transbay.n et...[color=blue]
>[color=green][color=darkred]
>> > Obviously the following doesn't work:[/color]
> >
> > int i = 5;
> > std::string myString = "Number is " + i + " thankyou please";[/color]
>[/color]
[color=blue]
> int i = 5;
> string myString1 = "The number is ";
> string myString2 = " thank you, please";
>
> ostringstream os;
>
> os << myString1 << i << myString2;
> string msgString = os.str();
>
> cout << msgString << endl;[/color]

Eek! Why isn't there anything nice, like a std::string ctor that takes an
int, so I could then do
"blah " + std::string(i) + " blah";

**Evan Carew** · Jul 22 '05, 04:02 PM

Re: std::string and integers

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Glen Able wrote:[color=blue]
> "Gwar" <xeno@xor.qua > wrote in message
> news:2004070801 4542.U17241@syn ergy.transbay.n et...
>[color=green][color=darkred]
>>>>Obviously the following doesn't work:
>>>
>>>int i = 5;
>>>std::strin g myString = "Number is " + i + " thankyou please";[/color]
>>[/color]
>[color=green]
>> int i = 5;
>> string myString1 = "The number is ";
>> string myString2 = " thank you, please";
>>
>> ostringstream os;
>>
>> os << myString1 << i << myString2;
>> string msgString = os.str();
>>
>> cout << msgString << endl;[/color]
>
>
> Eek! Why isn't there anything nice, like a std::string ctor that takes an
> int, so I could then do
> "blah " + std::string(i) + " blah";
>[/color]
There is, its called lexical cast & is part of the Boost library. look
at http://boost.org/libs/conversion/lexical_cast.htm

The code looks like the following:

string mystring;
mystring = "The number is " + lexical_cast<sh ort>(5) + " thank you, please";

Evan

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**John Harrison** · Jul 22 '05, 04:02 PM

Re: std::string and integers

> There is, its called lexical cast & is part of the Boost library. look[color=blue]
> at http://boost.org/libs/conversion/lexical_cast.htm
>
> The code looks like the following:
>
> string mystring;
> mystring = "The number is " + lexical_cast<sh ort>(5) + " thank you,[/color]
please";[color=blue]
>[/color]

Errm

lexical_cast<st ring>(5)

john

**John Harrison** · Jul 22 '05, 04:02 PM

Re: std::string and integers

"Glen Able" <smeREMOVEckler s@hotMEmail.com > wrote in message
news:ccjbi2$dua $1$8300dec7@new s.demon.co.uk.. .[color=blue]
>
> "Gwar" <xeno@xor.qua > wrote in message
> news:2004070801 4542.U17241@syn ergy.transbay.n et...[color=green]
> >[color=darkred]
> >> > Obviously the following doesn't work:
> > >
> > > int i = 5;
> > > std::string myString = "Number is " + i + " thankyou please";[/color]
> >[/color]
>[color=green]
> > int i = 5;
> > string myString1 = "The number is ";
> > string myString2 = " thank you, please";
> >
> > ostringstream os;
> >
> > os << myString1 << i << myString2;
> > string msgString = os.str();
> >
> > cout << msgString << endl;[/color]
>
> Eek! Why isn't there anything nice, like a std::string ctor that takes an
> int, so I could then do
> "blah " + std::string(i) + " blah";
>[/color]

Why would that be a good idea exactly?

If you want an operator to concatenate strings with integers there is
nothing stopping you writing it.

string operator+(const string& lhs, int rhs)
{
...
}

string operator+(int lhs, const string& rhs)
{
...
}

Don't blame me if the results don't match your expectations though.

john

**Glen Able** · Jul 22 '05, 04:02 PM

Re: std::string and integers

> If you want an operator to concatenate strings with integers there is[color=blue]
> nothing stopping you writing it.
>
> string operator+(const string& lhs, int rhs)
> {
> ...
> }[/color]

Ooh, didn't know you could do global operator overloads, ta.
In my excitement I just tried defining float operator+(float f1, float f2),
but the compiler's on to me :)
[color=blue]
> Don't blame me if the results don't match your expectations though.
>
> john[/color]

Do you have some specific problem in mind, John?

ta,
G.A.

**Rolf Magnus** · Jul 22 '05, 04:02 PM

Re: std::string and integers

Glen Able wrote:
[color=blue][color=green]
>> If you want an operator to concatenate strings with integers there is
>> nothing stopping you writing it.
>>
>> string operator+(const string& lhs, int rhs)
>> {
>> ...
>> }[/color]
>
> Ooh, didn't know you could do global operator overloads, ta.
> In my excitement I just tried defining float operator+(float f1, float
> f2), but the compiler's on to me :)[/color]

You can't overload operators with only built-in types as parameters.

**Glen Able** · Jul 22 '05, 04:03 PM

Re: std::string and integers

"Rolf Magnus" <ramagnus@t-online.de> wrote in message
news:ccjq8s$af7 $02$1@news.t-online.com...[color=blue]
> Glen Able wrote:
>[color=green][color=darkred]
> >> If you want an operator to concatenate strings with integers there is
> >> nothing stopping you writing it.
> >>
> >> string operator+(const string& lhs, int rhs)
> >> {
> >> ...
> >> }[/color]
> >
> > Ooh, didn't know you could do global operator overloads, ta.
> > In my excitement I just tried defining float operator+(float f1, float
> > f2), but the compiler's on to me :)[/color]
>
> You can't overload operators with only built-in types as parameters.[/color]

Evidently :)

Shame though. Would have been nice on a few occasions to help me trap dodgy
floating point operations. I did once even try globally redefining 'float'
as 'MyFloat' and supplying all the relevant operators, but ISTR there were
some unresolvable problems which would've meant fixing the usage in numerous
places. Actually, let me start a new thread on that...

cheers,
G.A.

**SaltPeter** · Jul 22 '05, 04:04 PM

Re: std::string and integers

"Glen Able" <smeREMOVEckler s@hotMEmail.com > wrote in message
news:ccj0ng$53r $1$830fa7a5@new s.demon.co.uk.. .[color=blue]
> Obviously the following doesn't work:
>
> int i = 5;
> std::string myString = "Number is " + i + " thankyou please";
>
> So can anyone give me some idea what's the nicest way to this sort of[/color]
thing?[color=blue]
> I'm sure it's not using sprintf.
>
> with thanks,
> G.A.
>[/color]

Why not consider a templated function? This way you can ostream other types,
not just an int.

// TtoStr.h
#include <string>
#include <sstream>

template<class T> std::string TtoStr(const T& r_t)
{
std::ostringstr eam ossbuffer;
ossbuffer << r_t;
return ossbuffer.str() ;
}

// main
#include <iostream>
#include "TtoString. h"

int main()
{
int i = 5;
double d = 2.0;

std::string s("int i = ");
s += TtoStr(i);
s += " and double d = ";
s += TtoStr(d);

std::cout << s << std::endl;

return 0;
}

**Rolf Magnus** · Jul 22 '05, 04:07 PM

Re: std::string and integers

Glen Able wrote:
[color=blue]
> Eek! Why isn't there anything nice, like a std::string ctor that
> takes an int,[/color]

There is. It will create a string of the specified size.