printf and string s

[Joah Senegal]

Hello all,

I'm trying to print a string on my screen... But the string comes from a
variable string... This is the code

#include <cstdlib>
#include <iostream>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
string t = "tes";
printf ("%s", t );
system("PAUSE") ;
return EXIT_SUCCESS;
}
But this isn;t working.... the program is crashing when doing printf...
anyone know how to fix this ?

[Tim Love]

"Joah Senegal" <bl****@hva.nlw rites:

>Hello all,

>I'm trying to print a string on my screen... But the string comes from a
variable string... This is the code

>#include <cstdlib>
#include <iostream>
#include <string>

>using namespace std;

>int main(int argc, char *argv[])
{
string t = "tes";
printf ("%s", t );
system("PAUSE") ;
return EXIT_SUCCESS;
}

>But this isn;t working.... the program is crashing when doing printf...
anyone know how to fix this ?

printf's expecting a C-style char-array "string". Give it what it wants
by using
printf ("%s", t.c_string());
or (better) use C++'s
cout << t;

[Stephane Wirtel]

Joah Senegal said the following on 14/09/2006 14:44:

Hello all,

I'm trying to print a string on my screen... But the string comes from a
variable string... This is the code

#include <cstdlib>
#include <iostream>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
string t = "tes";
printf ("%s", t );
system("PAUSE") ;
return EXIT_SUCCESS;
}

You try tu use std::string with printf.

printf is a function of library C

now, you can do it with t.c_str(), but it's not very c++ compliant.

try this code:

#include <iostream>
#include <string>

int main( int argc, char *argv[] ) {
std::string t = "tes";
std::cout << t;
return EXIT_SUCCESS;
}

[red floyd]

Joah Senegal wrote:

>
#include <cstdlib>
#include <iostream>
#include <string>

using namespace std;

int main(int argc, char *argv[])
{
string t = "tes";
printf ("%s", t );

cout << t << endl;

system("PAUSE") ;
return EXIT_SUCCESS;
}

If you *must* use printf, then pass t.c_str(), and you must include
<cstdio>. A std::string does not automagically convert to a char*. Why
did you include <iostreamif you weren't going to use it?

[Pete Becker]

Stephane Wirtel wrote:

You try tu use std::string with printf.

printf is a function of library C

now, you can do it with t.c_str(), but it's not very c++ compliant.

Code that uses it is well-formed and portable, so "compliant" here must
mean something else. Care to elaborate?

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.

[Stephane Wirtel]

Code that uses it is well-formed and portable, so "compliant" here must

mean something else. Care to elaborate?

I don't want to use C and C++ in the same source, it's C (printf, libc)
or C++ (std::cout, std::string, STL, ...) and not both.

Stephane

[Pete Becker]

Stephane Wirtel wrote:

>Code that uses it is well-formed and portable, so "compliant" here must
mean something else. Care to elaborate?

I don't want to use C and C++ in the same source, it's C (printf, libc)
or C++ (std::cout, std::string, STL, ...) and not both.

printf is C, but it's also C++. Does the fact that it's part of C
somehow pollute it? Do you also refuse to use sin, cos, etc. because
they're C?

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.

[Stephane Wirtel]

printf is C, but it's also C++. Does the fact that it's part of C

somehow pollute it? Do you also refuse to use sin, cos, etc. because
they're C?

You are right, sorry for my previous answer.

[Kai-Uwe Bux]

Pete Becker wrote:

Stephane Wirtel wrote:

>>Code that uses it is well-formed and portable, so "compliant" here must
mean something else. Care to elaborate?

I don't want to use C and C++ in the same source, it's C (printf, libc)
or C++ (std::cout, std::string, STL, ...) and not both.

printf is C, but it's also C++. Does the fact that it's part of C
somehow pollute it?

To some degree, it does: you are loosing a bit of typesafety by using the
printf() family. Otherwise, the compiler would have complained about the
OPs attempt to pass a std::string. This relates to their C heritage in that
strict typing is not that much of an issue in C (after all C does not use
type information for overload resolution and templates).

Besides, "pollute" is a loaded term and has a non-technical aspect to its
meaning. In that aesthetical sense, printf() clearly pollutes a program --
at least in my eyes :)

Do you also refuse to use sin, cos, etc. because they're C?

Nope, those are typesafe despite coming from C. (However, in my eyes these
also polute a program but for a different reason: you are calling a
function with a somewhat ill-defined contract: the standard says that
sin(x) computes the sin of x, which is a lie for almost all values of x.
What it actually computes is some unspecified approximation to the sin of
x. Thus, precision guarantess become a portability issue.)
Best

Kai-Uwe Bux

[Pete Becker]

Kai-Uwe Bux wrote:

Pete Becker wrote:

>Stephane Wirtel wrote:

>>>Code that uses it is well-formed and portable, so "compliant" here must
mean something else. Care to elaborate?
I don't want to use C and C++ in the same source, it's C (printf, libc)
or C++ (std::cout, std::string, STL, ...) and not both.

printf is C, but it's also C++. Does the fact that it's part of C
somehow pollute it?

To some degree, it does: you are loosing a bit of typesafety by using the
printf() family.

That's different. There are reasons to choose C++ streams, and reasons
to choose printf. There is no reason for a blanket refusal to use C,
which is what I was replying to.

>
Besides, "pollute" is a loaded term and has a non-technical aspect to its
meaning.

Yes, that's why I used it.

In that aesthetical sense, printf() clearly pollutes a program --
at least in my eyes :)

But, again, this wasn't about the merits of printf, but of C in general.

--

-- Pete

Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." For more information about this book, see
www.petebecker.com/tr1book.