"Not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation"

Question

I'm beginning a program using heaps in which I must insertSort, mergeSort, and quickSort into the heap. I was instructed to use the code from my textbook as a basis and I cannot even get the example code to compile. I keep receiving the error:

not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation

Now I think it has something to do with the order in which the template<> classes were declared in the Sort.h file. However, I can't imagine a textbook would publish code that simply doesn't compile. Would you guys mind taking a look?

Full errors:

In file included from Driver.cpp:4:0:
Sort.h: In instantiation of 'void heapsort(std::vector<Comparable>&) [with Comparable = int]':
Driver.cpp:47:21:   required from here
Sort.h:79:9: error: 'percDown' was not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation [-fpermissive]
Sort.h:104:6: note: 'template<class Comparable> void percDown(std::vector<Comparable>&, int, int)' declared here, later in the translation unit
Sort.h:83:9: error: 'percDown' was not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation [-fpermissive]
Sort.h:104:6: note: 'template<class Comparable> void percDown(std::vector<Comparable>&, int, int)' declared here, later in the translation unit
Sort.h: In instantiation of 'void mergeSort(std::vector<Comparable>&, std::vector<Comparable>&, int, int) [with Comparable = int]':
Sort.h:150:5:   required from 'void mergeSort(std::vector<Comparable>&) [with Comparable = int]'
Driver.cpp:53:22:   required from here
Sort.h:138:9: error: 'merge' was not declared in this scope, and no declarations were found by argument-dependent lookup at the point of instantiation [-fpermissive]
Sort.h:163:6: note: 'template<class Comparable> void merge(std::vector<Comparable>&, std::vector<Comparable>&, int, int, int)' declared here, later in the translation unit

Sort.h:

#ifndef SORT_H
#define SORT_H

/**
 * Several sorting routines.
 * Arrays are rearranged with smallest item first.
 */

#include <vector>
#include <functional>
using namespace std;

/**
 * Simple insertion sort.
 */
template <typename Comparable>
void insertionSort( vector<Comparable> & a )
{
    for( int p = 1; p < a.size( ); ++p )
    {
        Comparable tmp = std::move( a[ p ] );

        int j;
        for( j = p; j > 0 && tmp < a[ j - 1 ]; --j )
            a[ j ] = std::move( a[ j - 1 ] );
        a[ j ] = std::move( tmp );
    }
}


/**
 * Internal insertion sort routine for subarrays
 * that is used by quicksort.
 * a is an array of Comparable items.
 * left is the left-most index of the subarray.
 * right is the right-most index of the subarray.
 */
template <typename Comparable>
void insertionSort( vector<Comparable> & a, int left, int right )
{
    for( int p = left + 1; p <= right; ++p )
    {
        Comparable tmp = std::move( a[ p ] );
        int j;

        for( j = p; j > left && tmp < a[ j - 1 ]; --j )
            a[ j ] = std::move( a[ j - 1 ] );
        a[ j ] = std::move( tmp );
    }
}



/**
 * Shellsort, using Shell's (poor) increments.
 */
template <typename Comparable>
void shellsort( vector<Comparable> & a )
{
    for( int gap = a.size( ) / 2; gap > 0; gap /= 2 )
        for( int i = gap; i < a.size( ); ++i )
        {
            Comparable tmp = std::move( a[ i ] );
            int j = i;

            for( ; j >= gap && tmp < a[ j - gap ]; j -= gap )
                a[ j ] = std::move( a[ j - gap ] );
            a[ j ] = std::move( tmp );
        }
}

/**
 * Standard heapsort.
 */
template <typename Comparable>
void heapsort( vector<Comparable> & a )
{
    for( int i = a.size( ) / 2 - 1; i >= 0; --i )  /* buildHeap */
        percDown( a, i, a.size( ) );
    for( int j = a.size( ) - 1; j > 0; --j )
    {
        std::swap( a[ 0 ], a[ j ] );               /* deleteMax */
        percDown( a, 0, j );
    }
}

/**
 * Internal method for heapsort.
 * i is the index of an item in the heap.
 * Returns the index of the left child.
 */
inline int leftChild( int i )
{
    return 2 * i + 1;
}

/**
 * Internal method for heapsort that is used in
 * deleteMax and buildHeap.
 * i is the position from which to percolate down.
 * n is the logical size of the binary heap.
 */
template <typename Comparable>
void percDown( vector<Comparable> & a, int i, int n )
{
    int child;
    Comparable tmp;

    for( tmp = std::move( a[ i ] ); leftChild( i ) < n; i = child )
    {
        child = leftChild( i );
        if( child != n - 1 && a[ child ] < a[ child + 1 ] )
            ++child;
        if( tmp < a[ child ] )
            a[ i ] = std::move( a[ child ] );
        else
            break;
    }
    a[ i ] = std::move( tmp );
}

/**
 * Internal method that makes recursive calls.
 * a is an array of Comparable items.
 * tmpArray is an array to place the merged result.
 * left is the left-most index of the subarray.
 * right is the right-most index of the subarray.
 */
template <typename Comparable>
void mergeSort( vector<Comparable> & a,
                vector<Comparable> & tmpArray, int left, int right )
{
    if( left < right )
    {
        int center = ( left + right ) / 2;
        mergeSort( a, tmpArray, left, center );
        mergeSort( a, tmpArray, center + 1, right );
        merge( a, tmpArray, left, center + 1, right );
    }
}

/**
 * Mergesort algorithm (driver).
 */
template <typename Comparable>
void mergeSort( vector<Comparable> & a )
{
    vector<Comparable> tmpArray( a.size( ) );

    mergeSort( a, tmpArray, 0, a.size( ) - 1 );
}


/**
 * Internal method that merges two sorted halves of a subarray.
 * a is an array of Comparable items.
 * tmpArray is an array to place the merged result.
 * leftPos is the left-most index of the subarray.
 * rightPos is the index of the start of the second half.
 * rightEnd is the right-most index of the subarray.
 */
template <typename Comparable>
void merge( vector<Comparable> & a, vector<Comparable> & tmpArray,
            int leftPos, int rightPos, int rightEnd )
{
    int leftEnd = rightPos - 1;
    int tmpPos = leftPos;
    int numElements = rightEnd - leftPos + 1;

    // Main loop
    while( leftPos <= leftEnd && rightPos <= rightEnd )
        if( a[ leftPos ] <= a[ rightPos ] )
            tmpArray[ tmpPos++ ] = std::move( a[ leftPos++ ] );
        else
            tmpArray[ tmpPos++ ] = std::move( a[ rightPos++ ] );

    while( leftPos <= leftEnd )    // Copy rest of first half
        tmpArray[ tmpPos++ ] = std::move( a[ leftPos++ ] );

    while( rightPos <= rightEnd )  // Copy rest of right half
        tmpArray[ tmpPos++ ] = std::move( a[ rightPos++ ] );

    // Copy tmpArray back
    for( int i = 0; i < numElements; ++i, --rightEnd )
        a[ rightEnd ] = std::move( tmpArray[ rightEnd ] );
}


/**
 * Return median of left, center, and right.
 * Order these and hide the pivot.
 */
template <typename Comparable>
const Comparable & median3( vector<Comparable> & a, int left, int right )
{
    int center = ( left + right ) / 2;

    if( a[ center ] < a[ left ] )
        std::swap( a[ left ], a[ center ] );
    if( a[ right ] < a[ left ] )
        std::swap( a[ left ], a[ right ] );
    if( a[ right ] < a[ center ] )
        std::swap( a[ center ], a[ right ] );

        // Place pivot at position right - 1
    std::swap( a[ center ], a[ right - 1 ] );
    return a[ right - 1 ];
}

/**
 * Internal quicksort method that makes recursive calls.
 * Uses median-of-three partitioning and a cutoff of 10.
 * a is an array of Comparable items.
 * left is the left-most index of the subarray.
 * right is the right-most index of the subarray.
 */
template <typename Comparable>
void quicksort( vector<Comparable> & a, int left, int right )
{
    if( left + 10 <= right )
    {
        const Comparable & pivot = median3( a, left, right );

            // Begin partitioning
        int i = left, j = right - 1;
        for( ; ; )
        {
            while( a[ ++i ] < pivot ) { }
            while( pivot < a[ --j ] ) { }
            if( i < j )
                std::swap( a[ i ], a[ j ] );
            else
                break;
        }

        std::swap( a[ i ], a[ right - 1 ] );  // Restore pivot

        quicksort( a, left, i - 1 );     // Sort small elements
        quicksort( a, i + 1, right );    // Sort large elements
    }
    else  // Do an insertion sort on the subarray
        insertionSort( a, left, right );
}

/**
 * Quicksort algorithm (driver).
 */
template <typename Comparable>
void quicksort( vector<Comparable> & a )
{
    quicksort( a, 0, a.size( ) - 1 );
}


/**
 * Internal selection method that makes recursive calls.
 * Uses median-of-three partitioning and a cutoff of 10.
 * Places the kth smallest item in a[k-1].
 * a is an array of Comparable items.
 * left is the left-most index of the subarray.
 * right is the right-most index of the subarray.
 * k is the desired rank (1 is minimum) in the entire array.
 */
template <typename Comparable>
void quickSelect( vector<Comparable> & a, int left, int right, int k )
{
    if( left + 10 <= right )
    {
        const Comparable & pivot = median3( a, left, right );

            // Begin partitioning
        int i = left, j = right - 1;
        for( ; ; )
        {
            while( a[ ++i ] < pivot ) { }
            while( pivot < a[ --j ] ) { }
            if( i < j )
                std::swap( a[ i ], a[ j ] );
            else
                break;
        }

        std::swap( a[ i ], a[ right - 1 ] );  // Restore pivot

            // Recurse; only this part changes
        if( k <= i )
            quickSelect( a, left, i - 1, k );
        else if( k > i + 1 )
            quickSelect( a, i + 1, right, k );
    }
    else  // Do an insertion sort on the subarray
        insertionSort( a, left, right );
}

/**
 * Quick selection algorithm.
 * Places the kth smallest item in a[k-1].
 * a is an array of Comparable items.
 * k is the desired rank (1 is minimum) in the entire array.
 */
template <typename Comparable>
void quickSelect( vector<Comparable> & a, int k )
{
    quickSelect( a, 0, a.size( ) - 1, k );
}


template <typename Comparable>
void SORT( vector<Comparable> & items )
{
    if( items.size( ) > 1 )
    {
        vector<Comparable> smaller;
        vector<Comparable> same;
        vector<Comparable> larger;

        auto chosenItem = items[ items.size( ) / 2 ];

        for( auto & i : items )
        {
            if( i < chosenItem )
                smaller.push_back( std::move( i ) );
            else if( chosenItem < i )
                larger.push_back( std::move( i ) );
            else
                same.push_back( std::move( i ) );
        }

        SORT( smaller );     // Recursive call!
        SORT( larger );      // Recursive call!

        std::move( begin( smaller ), end( smaller ), begin( items ) );
        std::move( begin( same ), end( same ), begin( items ) + smaller.size( ) );
        std::move( begin( larger ), end( larger ), end( items ) - larger.size( ) );

/*
        items.clear( );
        items.insert( end( items ), begin( smaller ), end( smaller ) );
        items.insert( end( items ), begin( same ), end( same ) );
        items.insert( end( items ), begin( larger ), end( larger ) );
*/
    }
}

/*
 * This is the more public version of insertion sort.
 * It requires a pair of iterators and a comparison
 * function object.
 */
template <typename RandomIterator, typename Comparator>
void insertionSort( const RandomIterator & begin,
                    const RandomIterator & end,
                    Comparator lessThan )
{
    if( begin == end )
        return;

    RandomIterator j;

    for( RandomIterator p = begin+1; p != end; ++p )
    {
        auto tmp = std::move( *p );
        for( j = p; j != begin && lessThan( tmp, *( j-1 ) ); --j )
            *j = std::move( *(j-1) );
        *j = std::move( tmp );
    }
}

/*
 * The two-parameter version calls the three parameter version, using C++11 decltype
 */
template <typename RandomIterator>
void insertionSort( const RandomIterator & begin,
                    const RandomIterator & end )
{
    insertionSort( begin, end, less<decltype(*begin )>{ } );
}



#endif

And Driver.cpp

//Driver.cpp

#include <iostream>
#include "Sort.h"
#include <vector>
#include <string>
#include <time.h> 

using namespace std;

void checkSort( const vector<int> & a )
{
    for( int i = 0; i < a.size( ); ++i )
        if(a.size( ) != i )
            cout << "Error at " << i << endl;
    cout << "Finished checksort" << endl;
}

int main( )
{
    srand(time(NULL)); 

    int vec_length;

    cout << "What would you like the length of the vector to be?" << endl;
    cin >> vec_length;

    vector<int> a(vec_length);

    for(int i = 0; i < a.size(); i++)
    {
        a[i] = rand() % 100 + 1;
    }

    //vector<string> a( NUM_ITEMS );        // This input adds factor of N to running time
    //for( int i = 1; i < a.size( ); ++i )  // but we want to test std::move logic
      //  a[ i ] = a[ i - 1 ] + 'a';

    for( int theSeed = 0; theSeed < 10; ++theSeed )
    {
        insertionSort( a );
        checkSort( a );

        insertionSort( begin( a ), end( a ) );
        checkSort( a );

        heapsort( a );
        checkSort( a );

        shellsort( a );
        checkSort( a );

        mergeSort( a );
        checkSort( a );

        quicksort( a );
        checkSort( a );

        SORT( a );
        checkSort( a );

        quickSelect( a, vec_length / 2 );
        //cout << a[vec_length / 2 - 1].size( ) << " " << vec_length / 2 << endl;
    }

    cout << "Checking SORT, Fig 7.13" << endl;
    int N = vec_length * vec_length;
    vector<int> b( N );
    for( int i = 0; i < N; ++i )
        b[ i ] = i;
    SORT( b );
    for( int i = 0; i < N; ++i )
        if( b[ i ] != i )
            cout << "OOPS!!" << endl;

    return 0;
}

Answer 1

The order of declarations in C++ is very important. Template functions in particular have to be declared before they're used. The solution is to move the definition for e.g. percDown higher up in the file than its first use.