strings and referencing

Atomical · #1 04-Jul-2005, 19:29

I'm using the string library and I thought that because strings were passed by reference that I didn't need pointers. Right now the program isn't sending anything to standard output like it should be.

CPP / C++ / C Code:

#include <iostream>
#include <sys/types.h> 
#include <sys/stat.h> 
#include <fcntl.h> 
#include <unistd.h> 
#include <assert.h> 
#include <cstring>
#include <ctype.h>

using namespace std;

void test ( string s );


int main (int argc, char * const argv[]) {

string s;
test(s);
cout << s;

return 1;

}


void test ( string s ){
s = "asdfadfs";
}

cable_guy_67 · #2 04-Jul-2005, 20:46

First off, you will be more likely to get help by reading the how to post requests thread which will tell you how to use code tags. It gives some good pointers on including information as well.

Quote:

Originally Posted by Atomical

I'm using the string library and I thought that because strings were passed by reference that I didn't need pointers. Right now the program isn't sending anything to standard output like it should be.

Your problem is that you are not passing by reference you are passing by value. When s ends up in your test routine it sets the local variable s to "asdfadfs". The variable s in main is a different variable of the same name (with different scope if you will) and never gets set to anything.

Now, as you will see I will put the code between the code tags.

Code:


  CPP / C++ / C Code:
  // code will be here

CPP / C++ / C Code:

void test ( string s ){
s = "asdfadfs";
}

In order to charnge this change your function just a bit.

CPP / C++ / C Code:

void test ( string& s ){

Now you will be operating on the s from main when you are in test().

Is there a reason for all the excess in your includes? For your simple example you just need the following.

CPP / C++ / C Code:

#include <iostream>
#include <string>

using std::cout;
using std::string;
// using namespace std;

As you see, I commented out the using namespace std; and just used the using std::cout and string. They accomplish the same end result but are more limiting in what they actually include. There are quite a few posts that a search of the forum can dig up. If you don't like my method you could just go back to the using namespace std way and get rid of the using statement.

Mark

Atomical · #3 05-Jul-2005, 07:44

I should I be using the string library or should I be using character arrays? Is one faster than the other? Also, I put in the code you suggested and got the same result.

CPP / C++ / C Code:

#include <cstring>
#include <ctype.h>
#include <iostream>

using std::cout;
using std::string;


void test ( string s );


int main (int argc, char * const argv[]) {

string s;
test(s);
cout << s;

return 1;

}


void test ( string s ){
s = "asdfadfs";
}

Sokar · #4 05-Jul-2005, 08:01

Quote:

Originally Posted by Atomical

I should I be using the string library or should I be using character arrays? Is one faster than the other?

That question can bring a lot of debate. But I would say use string. They are easier to use and have many helpful member functions.

Quote:

Originally Posted by Atomical

Also, I put in the code you suggested and got the same result.

CPP / C++ / C Code:

#include <cstring>
#include <ctype.h>
#include <iostream>

using std::cout;
using std::string;


void test ( string s );


int main (int argc, char * const argv[]) {

string s;
test(s);
cout << s;

return 1;

}


void test ( string s ){
s = "asdfadfs";
}

That is not what was suggested. Add the "&".

CPP / C++ / C Code:

//#include <cstring>//string not here
#include <string>//string here
//#include <ctype.h>//old
#include <cctype>//standard
#include <iostream>

using namespace std;

void test ( string& s );

int main () {

	string s;
	test(s);
	cout << s;

	return 1;

}

void test ( string& s )
{
	s = "asdfadfs";
}

Also
Header Files
http://msdn.microsoft.com/library/de...eaders_stl.asp

<string>
http://msdn.microsoft.com/library/de...ing_header.asp

is not the same as
<cstring>
http://msdn.microsoft.com/library/de...ing_header.asp

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