Question

I’m a new code monkey in training, and I’m currently having issues working with arrays and structs.
Currently I have a main file where I have a an Array of Records declared. I pass that array to an external function, where a quick sort is performed on the with of the fields in the record. Mainly the first name. I’m having an issues where I copy elements in the array of records, to a temporary array for the sorting algorith. I know that c++ does have a qsort function built in, but for what I’m working on right now, I need to have the algoritm written out the way it is. I was able to get this to work using only any array.

I’m getting the following error when trying to compile with the make file.

make
g++    -c -o main2.o main2.cpp
g++ -c externArray2.cpp -o externArray2.o
externArray2.cpp: In function ‘void copytemp(EmployeeRecord*, EmployeeRecord*, int, int)’:
externArray2.cpp:52: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:53: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:54: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:55: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:56: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:57: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:58: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:59: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
externArray2.cpp:60: error: cannot convert ‘float’ to ‘void*’ for argument ‘1’ to ‘void* memcpy(void*, const void*, size_t)’
make: *** [externArray2.o] Error 1

Make File

test1:  main.o ExternArray.o
        g++ main.o ExternArray.o -o test1

externArray.o: ExternArray.cpp
        g++ -c ExternArray.cpp -o ExternArray.o

main.o: main.cpp
        g++ -c main.cpp -o main.o

Header.h

#ifndef _INCL_GUARD
#define _INCL_GUARD
const int maxEmployee =10;
const int NAMES = 5;
const int LENGTH = 15;


typedef struct EmployeeRecord
{
char first[10];
char last[10];
float reghours;
float ovrhours;
float pay;
float gross;
float defer;
float state;
float fed;
float ssi;
float net;
} EmployeeRecord;
#endif

main.cpp

#include <iostream>
#include <cstring>
using namespace std;
#include "./Header2.h"

void showArray(EmployeeRecord employees[], int, const char*);  //Function Prototype 3.1

extern void qsortArray(EmployeeRecord employees[], int, int);     //Funvtion Prototype      3.2

int main(void)
{
    EmployeeRecord myEmployee[maxEmployee];
    strcpy(myEmployee[0].first,"John");
    strcpy(myEmployee[0].last,"Doe");
    strcpy(myEmployee[1].first,"Ed");
    strcpy(myEmployee[1].last, "Whittle");
    strcpy(myEmployee[2].first, "Louise");
    strcpy(myEmployee[2].last, "Marion");
    strcpy(myEmployee[3].first,"Paula");
    strcpy(myEmployee[3].last, "Prentiss");
    strcpy(myEmployee[4].first, "Carl");
    strcpy(myEmployee[4].last, "Davidson");


    showArray(myEmployee, NAMES, "Before Sort");
    qsortArray(myEmployee, 0, 4 );
    showArray(myEmployee, NAMES, "After Sort");

return 0;               
}



void showArray(EmployeeRecord employees[], int emp, const char *message)
{
cout << message << endl;
for (int test = 0; test < emp; test++)
    {
    cout << "First Name: " << employees[test].first << endl;
    cout << "Last Name: " << employees[test].last << endl;

    }
}

ExternArray.cpp

#include <cstring>
#include <iostream>
#include <iomanip>
#include <stdio.h>
using namespace std;
#include "./Header2.h"

void qsortArray(EmployeeRecord employees[], int, int);     //Funvtion Prototype         3.2

void copytemp(EmployeeRecord tmpEmp[], EmployeeRecord emp[], int, int);

void qsortArray(EmployeeRecord employees[], int start, int finish)
{

int left=start,
    right=finish;
char  pivot[15];
strcpy(pivot, employees[(start+finish)/2].first);
  while (left < right) {
  cout << pivot << " pivot " << endl;
  cout << "outer loop" << endl;
    // find left candidate
    while (strcmp(employees[left].first,pivot) <0) left++; 
    // find right candidate 
    cout << "First Inner Loop" << endl;
    while (strcmp(employees[right].first,pivot) > 0 )right--; 
    cout << "Inner Loop" << endl;
    if (left <= right) 
        {
        EmployeeRecord tmpEmployee[1];
        cout << "Create new struct" << endl;
        copytemp(tmpEmployee, employees, 0, left);
        cout << "copy to temp" << endl;
        copytemp(tmpEmployee, employees, 1, right);
        copytemp(employees, tmpEmployee, left, 1);
        copytemp(employees, tmpEmployee, right, 0);

        left++;
        right--;
        cout << "All copy done" <<endl;
        } 
  } // while left < right
  cout << "Back out of outer Loop" << endl;
  if (start < right) qsortArray(employees,start,right);
  if (left < finish) qsortArray(employees,left,finish);
}

void copytemp(EmployeeRecord tmpEmp[], EmployeeRecord emp[], int first, int secound)
{
memcpy(tmpEmp[first].first, emp[secound].first, sizeof(emp[secound].first));
memcpy(tmpEmp[first].last, emp[secound].last, sizeof(emp[secound].last));
memcpy(tmpEmp[first].reghours, emp[secound].reghours, sizeof(emp[secound].reghours));
memcpy(tmpEmp[first].ovrhours, emp[secound].ovrhours, sizeof(emp[secound].ovrhours));
memcpy(tmpEmp[first].pay, emp[secound].pay, sizeof(emp[secound].pay));
memcpy(tmpEmp[first].gross, emp[secound].gross, sizeof(emp[secound].gross));
memcpy(tmpEmp[first].defer, emp[secound].defer, sizeof(emp[secound].defer));
memcpy(tmpEmp[first].state, emp[secound].state, sizeof(emp[secound].state));
memcpy(tmpEmp[first].fed, emp[secound].fed, sizeof(emp[secound].fed));
memcpy(tmpEmp[first].ssi, emp[secound].ssi, sizeof(emp[secound].ssi));
memcpy(tmpEmp[first].net, emp[secound].net, sizeof(emp[secound].net));
}

Answer 1

In C you can copy an entire struct with a plain assignment

tmpElm[first] = emp[secound];

This is only problematic if the struct contains members which are pointers, which is not your case.