Question

I am using the built in qsort to sort an array of structs. But after the call to qsort the last element in the array seems to have had its value that I am sorting by set to empty.

Here is my code…

int numEntries = 5;
TvEntry* entries[numEntries]; //create array

//Entries get added to the array here...

qsort( *entries, numEntries, sizeof(TvEntry*), &compareByName ); //sort

displayAll( entries, numEntries ); //display

//here is my sort method
int compareByName( const void* val1, const void* val2 )
{
    const TvEntry* entry1 = (TvEntry*)val1;
    const TvEntry* entry2 = (TvEntry*)val2;
    return strcasecmp( entry1->title, entry2->title );
}   

//here is my display method
void displayAll( TvEntry* entries[], int length )
{
    if( entries == NULL )
    {
        printf( "List is empty\n" );
    }
    else
    {
        int i = 0;
        for( i = 0; i < length; i++ )
        {
            printf( "ENTRY: %s\n", entries[i]->title );
        }
    }
}

I should mention that if i comment out the line which calls qsort then all entries are displayed correctly but when qsort is called then the entries are all displayed (Not Sorted) and printing a blank value for title for the last entry.

Answer 1

 qsort( *entries, numEntries, sizeof(TvEntry*), &compareByName);

is wrong, you don’t want to dereference the first element of your array. Make it

 qsort(entries, numEntries, sizeof(TvEntry*), &compareByName);

Furthermore, your compare funciton will receive pointers to the elements, and the elements are pointers, so it should be e.g.

int compareByName( const void* val1, const void* val2 )
{
    const TvEntry** entry1 = (TvEntry**)val1;
    const TvEntry** entry2 = (TvEntry**)val2;
    return strcasecmp( (*entry1)->title, (*entry2)->title );
}