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Soulstorm
Jan 22, 2006, 09:58 AM
I am stydying C++ for my exams. So, I am trying to do an exercise concerning templates . You don't need to know the question, since my question is not related to how can I do the exercise but rather a strange thing I want to verify:

My code is this:
#include <iostream>
#include <string>
using namespace std;


template<class T>
void set(T p[], int num, char *name){
int i;
for(i=0; i<num; i++){
cout << name << "[" << i << "]=";
cin >> p[i];
}
}

template<class T>
void show(T p[], int num, char *name){
int i;
for(i=0; i<num; i++){
cout << name << "[" << i << "]=" << p[i] << "\n";
}
}

template<class T>
int greater(T a, T b){return(a>b);}
int greater(char *a, char *b){return strcmp(a,b)>0;}

template<class T>
void swap(T &a, T &b){
T temp = a;
a = b;
b = temp;
}
void swap(char *a, char *b){
char temp[20];
strcpy(temp, a);
strcpy(a,b);
strcpy(b,temp);
}

template <class T>

void sort(T p[], int size){
int i,k;
for(k=1;k<size;k++)
for(i=0;i<size-k;i++)
if (greater(p[i],p[i+1])>0){
swap(p[i],p[i+1]);
}
}


int main(){
char names[4][21]; int n=4;
set(names,n,"names");
cout<<"\nunsorted names a\n";
show(names,n,"names");
sort(names,n);
cout<<"\nsorted names\n";
show(names,n,"names");
int numbers[4];
set(numbers,3,"numbers");
cout<<"\nunsorted numbers b\n";
show(numbers,3,"numbers");
sort(numbers,3);
cout<<"\nsorted numbers\n";
show(numbers,3,"numbers");

}

And it shows many errors in xCode. The errors have something to do with ambiguous declarations.

I change my code to this:
#include <iostream.h>
#include <string.h>


template<class T>
void set(T p[], int num, char *name){
int i;
for(i=0; i<num; i++){
cout << name << "[" << i << "]=";
cin >> p[i];
}
}

template<class T>
void show(T p[], int num, char *name){
int i;
for(i=0; i<num; i++){
cout << name << "[" << i << "]=" << p[i] << "\n";
}
}

template<class T>
int greater(T a, T b){return(a>b);}
int greater(char *a, char *b){return strcmp(a,b)>0;}

template<class T>
void swap(T &a, T &b){
T temp = a;
a = b;
b = temp;
}
void swap(char *a, char *b){
char temp[20];
strcpy(temp, a);
strcpy(a,b);
strcpy(b,temp);
}

template <class T>

void sort(T p[], int size){
int i,k;
for(k=1;k<size;k++)
for(i=0;i<size-k;i++)
if (greater(p[i],p[i+1])>0){
swap(p[i],p[i+1]);
}
}


int main(){
char names[4][21]; int n=4;
set(names,n,"names");
cout<<"\nunsorted names a\n";
show(names,n,"names");
sort(names,n);
cout<<"\nsorted names\n";
show(names,n,"names");
int numbers[4];
set(numbers,3,"numbers");
cout<<"\nunsorted numbers b\n";
show(numbers,3,"numbers");
sort(numbers,3);
cout<<"\nsorted numbers\n";
show(numbers,3,"numbers");

}
and it compiles fine. (Note that I have changed the headers and removed the namespace). Lastly, with a little thought, I ended up using this code:
#include <iostream>
#include <string>

using std::cout;
using std::cin;

template<class T>
void set(T p[], int num, char *name){
int i;
for(i=0; i<num; i++){
cout << name << "[" << i << "]=";
cin >> p[i];
}
}

template<class T>
void show(T p[], int num, char *name){
int i;
for(i=0; i<num; i++){
cout << name << "[" << i << "]=" << p[i] << "\n";
}
}

template<class T>
int greater(T a, T b){return(a>b);}
int greater(char *a, char *b){return strcmp(a,b)>0;}

template<class T>
void swap(T &a, T &b){
T temp = a;
a = b;
b = temp;
}
void swap(char *a, char *b){
char temp[20];
strcpy(temp, a);
strcpy(a,b);
strcpy(b,temp);
}

template <class T>

void sort(T p[], int size){
int i,k;
for(k=1;k<size;k++)
for(i=0;i<size-k;i++)
if (greater(p[i],p[i+1])>0){
swap(p[i],p[i+1]);
}
}


int main(){
char names[4][21]; int n=4;
set(names,n,"names");
cout<<"\nunsorted names a\n";
show(names,n,"names");
sort(names,n);
cout<<"\nsorted names\n";
show(names,n,"names");
int numbers[4];
set(numbers,3,"numbers");
cout<<"\nunsorted numbers b\n";
show(numbers,3,"numbers");
sort(numbers,3);
cout<<"\nsorted numbers\n";
show(numbers,3,"numbers");

}
(note that I included the specific statements to be used from the std namespace).

So i figured out it is a namespace problem. What are the commands that conflict with each other exactly?

Finally, do you know of any good reference to the commands each available namespace includes? I figured out that if I want to do some serious programming, I should get involved with namespaces and templates a lot, even if my exams don't require that.



kainjow
Jan 22, 2006, 11:23 AM
Are you compiling with GCC 4?

Soulstorm
Jan 22, 2006, 02:36 PM
Are you compiling with GCC 4?
yup. But it has the same problems under GCC 3.x

it doesn't matter what compiler I use. I get errors.

anyway this is a namespace problem. Do you know of any good reference on namespaces?

AlmostThere
Jan 22, 2006, 05:23 PM
"greater" and "swap" are both part of the standard library as is "sort" for that matter but the definitions do not clash.

Don't use "using namespace std"

Any (in fact every) c++ reference should tell you this.