C++, function using references not working. Advice?

[kyeana]

I just started using C++, and im currently working on using references to do multiple returns.

This sample code simply swaps two ints:
[cpp]
#include <iostream>
using namespace std;

int main()
{
int x =12;
int y =21;

cout << "x is: " << x <<endl;
cout << "y is: " << y << endl;

swap(x,y);

cout << "new x is: " << x << endl;
cout << "new y is: " << y << endl;

return 0;
}

void swap(int &rX, int &rY)
{
int temp;

temp = rX;
rX = rY;
rY = temp;
}
[/cpp]

This code works fine, they get swapped and all is happy.

However, when i try doing the same thing but swapping 3 ints i get a compiler error "basic_ref.cpp:15: error: no matching function for call to ‘swap(int&, int&, int&)'". Is there a limit to the number of references i can pass into a function? Or am i just doing something wrong with my code?

[cpp]
#include <iostream>
using namespace std;

int main()
{
int x =12;
int y =21;
int z = 17;

cout << "x is: " << x <<endl;
cout << "y is: " << y << endl;
cout << "z is: " << z << endl;

swap(x,y,z);

cout << "new x is: " << x << endl;
cout << "new y is: " << y << endl;
cout << "new z is: " << z << endl;

return 0;
}

void swap(int &rX, int &rY, int &rZ)
{
int temp;

temp = rX;
rX = rY;
rY = rZ;
rZ = temp;
}
[/cpp]

BTW, i am using the GCC 4.4.1 compiler if that makes any difference.

 

[saint19]

maybe this can help you

http/msdn.microsoft.com/en-us/library/s5120k8y%28VS.71%29.aspx

How i see, you don't load the <string> library

 

[kyeana]

No offense, but did you even look at my code? I am using integers, not strings, therefore there is no reason to #include <string>.

The first code that i posted (with only 2 references being passed in) works, and the integers are swapped. However the second code (with 3 references being passed in) gives me an error at compile time.

Any other advice as to why this might not be working? Could it be a limitation of C++? a compiler issue? just bad coding on my part?

Thanks

 

[randomizer]

If it is anything like C# I don't think there's any (practical) limit to the number of references you can send, however my knowledge of C++ is pretty poor. It's a rather odd error, I can't see anything glaringly wrong with the function call or signature. It's possible that because there is a "built-in" swap function (or appears to be based on the article linked above) there might be issues with overloading it. Have you tried calling the function something else?

 

[kyeana]

When i initally wrote this code it had a different name and didn't work, however ill try it again when i get home.

My first thought is that the name shouldn't be a problem for two reasons. First, the swap method shown above is part of <string>, and sense i haven't included that it seems like there would be nothing there to overload, and secondly the first swap function works while the second one doesn't.

Ill try it again with a different name, and if that doesn't work ill try a different compiler and post back with how it fares

 

[mindless728]

you need a function prototype

void swap(int &, int &, int &);

before main and it is generally accepted to have this after the include and using statements

 

[randomizer]

you need a function prototype

void swap(int &, int &, int &);

before main and it is generally accepted to have this after the include and using statements

I vaguely remember something about that from my basic C++ classes years ago.

 

[kyeana]

Done and done. Thanks for the info.

Do you know why it worked with the 2 references but failed with the 3 references without the prototype? Not that it really matters, i will make sure to include these in the prototype in the cpp or header file from now on, i am just curious.

Thanks for the help.

 

[mindless728]

my guess, there is a function prototype for it in one of the header files used for iostream, though you would have to look closely at what gcc includes

 

[Zenthar]

As mindless728 said, one way is to declare a function prototype, but you can also just declare the function before using it (put swap() before main()).

 

[randomizer]

As mindless728 said, one way is to declare a function prototype, but you can also just declare the function before using it (put swap() before main()).

Bah, now I remember one of the first things I learned back in C++ classes. Put main() at the bottom! :lol: I've been working with C# now mostly, and positioning doesn't make a difference, so those kinds of "rules" quickly get forgotten.

 

[mindless728]

Bah, now I remember one of the first things I learned back in C++ classes. Put main() at the bottom! :lol: I've been working with C# now mostly, and positioning doesn't make a difference, so those kinds of "rules" quickly get forgotten.

or you can put the prototypes on top and then the definitions on the bottom
or put them in a header file and include that

 

[randomizer]

They don't teach you that in basic C++. This was very basic high school stuff.

 

[mindless728]

well, i never took c++ in high school, i learned asm for the z80 and m68k, not until college did i get into c++ work

 

[randomizer]

Well if you know asm, you can consider yourself 1337 right? 😀 You can now write programs to run precisely how you want them, it just might take you a bit longer 😉

 

[mindless728]

well for my major you would have to know asm (at least one)