DaniWeb Forum Index > Software Development > C++

C++ RSS

Passing data between C++ programs

Please support our C++ advertiser: Intel Parallel Studio Home

Thread Solved

•

Join Date: Apr 2008

Posts: 7

Reputation: wiglaf is an unknown quantity at this point

Solved Threads: 0

wiglaf

Offline

Newbie Poster

Passing data between C++ programs

Mar 15th, 2009

I have been searching my texts, the web, and DaniWeb for information about how to share data between compiled C++ executables. I've been studying extern variables and named pipes without success. A typical program calls another program like this:

float Pi = 3.14;
system("AdjustSeaLevel.exe Pi 5.4 11.2 c f g");

and a typical receiving program looks like this:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int main(int argc, char* argv[])
{
float Pi;
// Confirm the args passed OK
   for(int i=0;i<argc;i++)
     cout << "Parameter argv[" << i << "]  = " << argv[i] << endl;
 
// Then convert literals (5.4, 11.2, etc.) to floats:
   float Celsius = atof(argv[2]);
   float Fahrenheit = atof(argv[3]);
 
// Then confirm literal successfully converted to float:
   Celsius = Celsius / 2; // etc.
 
// Or work with passed literals in other ways:
   if(argv[4][0] == 'c') cout << "Calculate in Celsius! " << endl; // etc.
}
int main(int argc, char* argv[])
{
float Pi;
// Confirm the args passed OK
   for(int i=0;i<argc;i++)
     cout << "Parameter argv[" << i << "]  = " << argv[i] << endl;

// Then convert literals (5.4, 11.2, etc.) to floats:
   float Celsius = atof(argv[2]);
   float Fahrenheit = atof(argv[3]);

// Then confirm literal successfully converted to float:
   Celsius = Celsius / 2; // etc.

// Or work with passed literals in other ways:
   if(argv[4][0] == 'c') cout << "Calculate in Celsius! " << endl; // etc.
}

And everything works fine, but the Pi variable passed by the calling program,

float Pi = 3.14;
system("AdjustSeaLevel.exe Pi 5.4 11.2 c f g");

arrives in called prog as a literal "Pi". I don't know how to substitute
the variable into the calling program's parameters.

One way around this of course is to have the calling prog store the needed piece of data in a disk file and then have the called prog open the file and retrieve the data, which in eff lets the disk function as a "pipe." But that requires a disk read and code that I would rather avoid if possible.

If someone knows a way to do this, I would like to know. Thanks, wiglaf.

Last edited by Ancient Dragon; Mar 15th, 2009 at 10:50 pm. Reason: add code tags

•

Join Date: Aug 2008

Posts: 149

Reputation: monkey_king is on a distinguished road

Solved Threads: 8

monkey_king monkey_king is offline

Offline

Junior Poster

Re: Passing data between C++ programs

Mar 15th, 2009

whats your platform?

•

Join Date: Dec 2004

Posts: 2,413

Reputation: Comatose is a jewel in the rough

Solved Threads: 211

Comatose

Offline

Taboo Programmer

Re: Passing data between C++ programs

Mar 15th, 2009

you can't concatenate it?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
float Pi = 3.14;
system("AdjustSeaLevel.exe " + Pi + " 5.4 11.2 c f g");
float Pi = 3.14;
system("AdjustSeaLevel.exe " + Pi + " 5.4 11.2 c f g");

or make a variable that contains the string to pass in, and then issue that?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
#include <cstdio>
#include <cstring>
#include <sstream>
 
using namespace std;
 
int main(int argc, char **argv)
{
	float Pi = 3.14;
	std::string tosend; 
	std::ostringstream buff;
	buff << Pi;
 
	tosend = buff.str() + " 5.4 11.2 c f g";
	cout << "something " + tosend;
	return 0;
}
#include <iostream>
#include <cstdio>
#include <cstring>
#include <sstream>

using namespace std;

int main(int argc, char **argv)
{
	float Pi = 3.14;
	std::string tosend; 
	std::ostringstream buff;
	buff << Pi;

	tosend = buff.str() + " 5.4 11.2 c f g";
	cout << "something " + tosend;
	return 0;
}

Last edited by Comatose; Mar 15th, 2009 at 3:51 pm.

•

Join Date: Apr 2008

Posts: 7

Reputation: wiglaf is an unknown quantity at this point

Solved Threads: 0

wiglaf

Offline

Newbie Poster

Re: Passing data between C++ programs

Mar 15th, 2009

•

Originally Posted by Comatose

you can't concatenate it?
Help with Code Tags

C++ Syntax (Toggle Plain Text)
float Pi = 3.14;
system("AdjustSeaLevel.exe " + Pi + " 5.4 11.2 c f g");
float Pi = 3.14; system("AdjustSeaLevel.exe " + Pi + " 5.4 11.2 c f g");
or make a variable that contains the string to pass in, and then issue that?
Help with Code Tags

C++ Syntax (Toggle Plain Text)
#include <iostream>
#include <cstdio>
#include <cstring>
#include <sstream>
 
using namespace std;
 
int main(int argc, char **argv)
{
	float Pi = 3.14;
	std::string tosend; 
	std::ostringstream buff;
	buff << Pi;
 
	tosend = buff.str() + " 5.4 11.2 c f g";
	cout << "something " + tosend;
	return 0;
}
#include <iostream> #include <cstdio> #include <cstring> #include <sstream> using namespace std; int main(int argc, char **argv) { float Pi = 3.14; std::string tosend; std::ostringstream buff; buff << Pi; tosend = buff.str() + " 5.4 11.2 c f g"; cout << "something " + tosend; return 0; }

Comatose, thanks for your suggestions. I am using Windows XP, Borland Builder 4 and its built-in editor and compiler. I tried your first suggestion--with those headers,

system("AdjustSeaLevel.exe " + Pi + " 5.4 11.2 c f g");

which generated a floating point error, and then I tried your second group of code, which compiles OK, and I confirm in the calling program that the "tosend" string does correctly hold the desired floating poing Pi, and then I try to pass tosend to the receiving program with

system("AdjustSeaLevel.exe tosend");

but a literal "tosend" arrives in the called program (AdjustSeaLevel.exe), so what I'm missing is how to pass the variable to the called program. wiglaf

•

Join Date: Dec 2004

Posts: 2,413

Reputation: Comatose is a jewel in the rough

Solved Threads: 211

Comatose

Offline

Taboo Programmer

Re: Passing data between C++ programs

Mar 15th, 2009

you can't put variables inside double quotes. That means it's a literal string then. You want the value of the variable, so you must take it out of the quotes..... You can't just take it out of quotes either, you must concatenate it.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
system("AdjustSeaLevel.exe " + tosend);
system("AdjustSeaLevel.exe " + tosend);

•

Join Date: Apr 2008

Posts: 7

Reputation: wiglaf is an unknown quantity at this point

Solved Threads: 0

wiglaf

Offline

Newbie Poster

Re: Passing data between C++ programs

Mar 15th, 2009

•

Originally Posted by Comatose

you can't put variables inside double quotes. That means it's a literal string then. You want the value of the variable, so you must take it out of the quotes..... You can't just take it out of quotes either, you must concatenate it.
Help with Code Tags

C++ Syntax (Toggle Plain Text)
system("AdjustSeaLevel.exe " + tosend);
system("AdjustSeaLevel.exe " + tosend);

Comatose, that was my reasoning also, and your suggestion

system("AdjustSeaLevel.exe " + tosend;

was one of the first I tried. It generates these compiler errors:

Cannot convert 'string' to 'const char *' and
Type mismatch in parameter '__command' (wanted 'const char *', got 'string').

The entire program now looks like:

#include <conio.h>
#include <iostream.h>
#include <cstdio.h>
#include <cstring.h>
#include <sstream.h>
using namespace std;
#pragma argsused
int main(int argc, char* argv[])
{
float Pi = 3.14;
std::string tosend;
std::ostringstream buff;
buff << Pi;
tosend = buff.str() + " 5.4 11.2 c f g";
system("AdjustSeaLevel.exe " + tosend);
getch();
return 0;
}
I appreciate the time you've spent looking at this code. wiglaf

•

Join Date: Mar 2009

Posts: 33

Reputation: Zcool31 is an unknown quantity at this point

Solved Threads: 1

Zcool31

Offline

Light Poster

Re: Passing data between C++ programs

Mar 15th, 2009

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
#include <sstream>
int main(int argc, char** argv){
//...
//your code here
//...
 
stringstream toPass;
 
toPass << "AdjustSealevel.exe" << Pi;
 
system(toPass.cstr());   //it might me c_str() instead of cstr() not too sure
 
EXIT_SUCCESS;
}
#include <sstream>
int main(int argc, char** argv){
//...
//your code here
//...

stringstream toPass;

toPass << "AdjustSealevel.exe" << Pi;

system(toPass.cstr());   //it might me c_str() instead of cstr() not too sure

EXIT_SUCCESS;
}

Help with Code Tags

(Toggle Plain Text)

class NoClass {
	~NoClass () { delete this; }
};

•

Join Date: Dec 2004

Posts: 2,413

Reputation: Comatose is a jewel in the rough

Solved Threads: 211

Comatose

Offline

Taboo Programmer

Re: Passing data between C++ programs

Mar 15th, 2009

Yeah, it's .c_str()

•

Join Date: Oct 2007

Posts: 792

Reputation: siddhant3s has much to be proud of

Solved Threads: 135

siddhant3s siddhant3s is offline

Offline

Master Poster

Re: Passing data between C++ programs

Mar 16th, 2009

>>Yeah, it's .c_str()
NO. it is .str() for string streams.It will return a string object on which you will have to do a .c_str(). So the corrected code would be somewhat like this:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include<iostream>
#include<sstream>
int main()
{
    std::stringstream arg;
    const float pi=3.145745;
    arg<<"AdjustSealevel.exe "<<pi;
 
    std::cout<<arg.str().c_str();
    system(  arg.str().c_str()  );
}
#include<iostream>
#include<sstream>
int main()
{
    std::stringstream arg;
    const float pi=3.145745;
    arg<<"AdjustSealevel.exe "<<pi;

    std::cout<<arg.str().c_str();
    system(  arg.str().c_str()  );
}

Siddhant Sanyam
(Not posting much)
Migrate to Standard C++ :When to tell your C++ Code is Non-Standard.
Please Read before posting: How To Ask Questions The Smart Way

•

Join Date: Apr 2008

Posts: 7

Reputation: wiglaf is an unknown quantity at this point

Solved Threads: 0

wiglaf

Offline

Newbie Poster

Re: Passing data between C++ programs

#10

Mar 16th, 2009

•

Originally Posted by siddhant3s

>>Yeah, it's .c_str()
NO. it is .str() for string streams.It will return a string object on which you will have to do a .c_str(). So the corrected code would be somewhat like this:
Help with Code Tags

C++ Syntax (Toggle Plain Text)
#include<iostream>
#include<sstream>
int main()
{
    std::stringstream arg;
    const float pi=3.145745;
    arg<<"AdjustSealevel.exe "<<pi;
 
    std::cout<<arg.str().c_str();
    system(  arg.str().c_str()  );
}
#include<iostream> #include<sstream> int main() { std::stringstream arg; const float pi=3.145745; arg<<"AdjustSealevel.exe "<<pi; std::cout<<arg.str().c_str(); system( arg.str().c_str() ); }

siddhant3s, your code works. I can now successfully pass the variable pi from a calling program, and it is received by the called program, and I verify it is a true float. I have also succ mixed literals with the passed string, as in

arg << "AdjustSealevel.exe c d e " << pi ;

and confirmed they are succ passed, but one task I have not solved is how to pass more than one variable, as in

float DO_Reading = 99.99;
arg << "AdjustSealevel.exe c d e " << pi + DO_Reading +
OtherVarsEtc ; // error

Can you tell me what mistake I am making? wiglaf