Can't seem to find the error here.

Just been doing some coding recently, and I am getting an error in this snippet of code:

Code:

	template <class T>
	void RemoveElement ( vector <T> hay_stack, T needle )
	{
		vector<T>::iterator iter = hay_stack.begin();
		while ( iter != hay_stack.end() && (*iter) != needle ) iter++;
		if ( (*iter) == needle ) hay_stack.erase ( iter );
	}

It tells me " expected `;' before 'iter' ". At first I thought I had forgot a semicolon somewhere else in the file that then caused this error to be thrown, but I don't see any.

Here's the whole file:

Code:

#ifndef __AGENTS_SIMULATION_H
#define __AGENTS_SIMULATION_H

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <vector>

using namespace std;

#include "world.h"

namespace AgentsSimulation
{
	extern World SimulatedWorld;

	void InitializeSimulation ( );
	void RunIteration ( );

	template <class T>
	int FindVectorElement ( vector <T> hay_stack, T needle )
	{
		for ( unsigned int x = 0; x < hay_stack.size(); x++ )
		{
			if ( hay_stack[x] == needle ) return x;
		}

		return -1;
	}

	template <class T>
	void RemoveElement ( vector <T> hay_stack, T needle )
	{
		vector<T>::iterator iter = hay_stack.begin();
		while ( iter != hay_stack.end() && (*iter) != needle ) iter++;
		if ( (*iter) == needle ) hay_stack.erase ( iter );
	}
}

#endif /* __AGENTS_SIMULATION_H */

Try:

Code:

	template <class T>
	void RemoveElement ( vector <T> hay_stack, T needle )
	{
		typename vector<T>::iterator iter = hay_stack.begin();
		while ( iter != hay_stack.end() && (*iter) != needle ) iter++;
		if ( (*iter) == needle ) hay_stack.erase ( iter );
	}

(Since at compile time it is not really known it is a type)

iterator is a qualified dependent type on T so you throw a "typename" in front of it.

Some other things:
"stdio.h, stdlib.h, time.h" - there are C++ headers for these
"vector <T> hay_stack" - that's being passed by value (a copy is made) and can be const for FindVectorElement() since it isn't modified.
"using namespace std" - never in a header
"iter++" - use pre-increment on iterators
"if ( (*iter) == needle )" - iter could be pointer to the end(), check for "!= end()"
"T needle" - could be const reference in both functions
"FindVectorElement" - there's already a general "find()" in <algorithm>
"RemoveElement" - this could also be done with the "remove-erase" idiom if you wanted to remove all instances

gg

I usually like to think like this:
If you are trying to use a type declared in a template class or struct (anything that requires a type, basically) and it is an unknown type (ie T, as in your example), then you must add "typename" before it.
If it is a known type (ie int), then it is not required.

Originally Posted by Elysia

If you are trying to use a type declared in a template class or struct (anything that requires a type, basically) and it is an unknown type (ie T, as in your example), then you must add "typename" before it.

Although that works as a rule of thumb, a more minimalistic rule of thumb would be: if you are trying to use a type name declared in a template and it depends on a template parameter, e.g., T::name where T is a template parameter, then you must use typename to disambiguiate the type name from a member name. This corresponds to the reasoning provided by Codeplug.

Yes, yes, something like that. That is my line of reasoning.
If it is a type that somehow involves an unknown type (eg T), then typename must be used if it is a type.