CODE A:
vector< int >::const_reverse_iterator rcit;
vector< int >::const_reverse_iterator tit=v.rend();
for(rcit = v.rbegin(); rcit != tit; ++rcit)
cout << *rcit << " ";
CODE B:
vector< int >::const_reverse_iterator rcit;
for(rcit = v.rbegin(); rcit != v.rend(); ++rcit)
cout << *rcit << " ";
CODE A works fine but why does CODE B throughs error :
DEV C++\vector_test.cpp no match for 'operator!=' in 'rcit != std::vector<_Tp, _Alloc>::rend() with _Tp = int, _Alloc = std::allocator'.
This is the program I was trying to write.
#include <iostream>
using std::cout;
using std::cin;
using std::endl;
using namespace std;
#include <vector>
using std::vector;
template< typename T > void printVector( const vector< T > &v);
template< typename T >
void printVector( const vector< T > &v)
{
typename vector< T >::const_iterator cit;
for(cit = v.begin(); cit != v.end(); ++cit)
cout << *cit << " ";
}
int main()
{
int number;
vector< int > v;
cout << "Initial size of the vector : " << v.size()
<< " and capacity : " << v.capacity() << endl;
for(int i=0; i < 3; i++)
{
cout << "Enter number : ";
cin >> number;
v.push_back(number);
}
cout << "Now size of the vector : " << v.size()
<< "and capacity : " << v.capacity() << endl;
cout << "output vector using iterator notation " << endl;
printVector(v);
cout << "Reverse of output ";
vector< int >::const_reverse_iterator rcit;
for(rcit = v.rbegin(); v.rend() != rcit ; ++rcit)
cout << *rcit << " ";
cin.ignore(numeric_limits< streamsize >::max(开发者_JS百科), '\n');
cin.get();
return 0;
}
The problem is there are two forms of the rend
method:
reverse_iterator rend();
const_reverse_iterator rend() const;
When doing the comparison it seems the first is being used (though I don't know why), and the operator !=
for comparing a 'const' and a 'non-const' iterator is not defined. When assigning to the variable though, the compiler can deduce the correct function to call and it all works correctly.
I don't get any errors or warnings when I compile the following in Xcode 4 or codepad:
#include <iostream>
#include <vector>
int main () {
using namespace std;
vector< int > v;
vector< int >::const_reverse_iterator rcit;
for(rcit = v.rbegin(); rcit != v.rend(); ++rcit)
cout << *rcit << " ";
}
Does your program differ from this in any significant way? What compiler are you using? Does ognian's suggestion work? And what if you replace the !=
with an ==
? (I know it would cause a run-time error but I curious about the compiler's response to this.)
Try swapping the operands of != like this:
for(rcit = v.rbegin(); v.rend() != rcit; ++rcit)
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