I don't what is the meaning of these errors

[nanger]

in the debugging of my program below, I found that before that the sort_merge(b,size) is about to return to the main()
the local variable array b[]=2 3 4 5 5 7 9
so the sort_merge() seems to function successfully
why the errors happen when this function is about to return?

#include <iostream> 
#include <fstream>
#include <string>
using namespace std; 
 

int main()
{
  int b[]={2,9,5,7,4,3,5};
  int size=sizeof(b)/sizeof(b[0]);
  cout<<size<<endl;
  sort_merge(b,size);
  for(int i=0;i<size;i++)
  {
    cout<<b[i]<<" ";
  }
  cout<<endl;
 return 0;
}

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

nanger@nanger-laptop:~/Desktop/try$ ./test 7 *** glibc detected *** ./test: double free or corruption (!prev): 0x0804a018 *** ======= Backtrace: ========= /lib/tls/i686/cmov/libc.so.6[0xb7d75a85] /lib/tls/i686/cmov/libc.so.6(cfree+0x90)[0xb7d794f0] /usr/lib/libstdc++.so.6(_ZdlPv+0x21)[0xb7f41b11] /usr/lib/libstdc++.so.6(_ZdaPv+0x1d)[0xb7f41b6d] ./test(__gxx_personality_v0+0x399)[0x8048aad] ./test[0x8048b2e] /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe0)[0xb7d20450] ./test(__gxx_personality_v0+0x3d)[0x8048751] ======= Memory map: ======== 08048000-08049000 r-xp 00000000 08:09 196042 /home/nanger/Desktop/try/test 08049000-0804a000 rw-p 00000000 08:09 196042 /home/nanger/Desktop/try/test 0804a000-0806b000 rw-p 0804a000 00:00 0 [heap] b7c00000-b7c21000 rw-p b7c00000 00:00 0 b7c21000-b7d00000

b7d09000-b7d0a000 rw-p b7d09000 00:00 0 b7d0a000-b7e53000 r-xp 00000000 08:09 343633 /lib/tls/i686/cmov/libc-2.7.so b7e53000-b7e54000 r--p 00149000 08:09 343633 /lib/tls/i686/cmov/libc-2.7.so b7e54000-b7e56000 rw-p 0014a000 08:09 343633 /lib/tls/i686/cmov/libc-2.7.so b7e56000-b7e59000 rw-p b7e56000 00:00 0 b7e59000-b7e63000 r-xp 00000000 08:09 310084 /lib/libgcc_s.so.1 b7e63000-b7e64000 rw-p 0000a000 08:09 310084 /lib/libgcc_s.so.1 b7e64000-b7e65000 rw-p b7e64000 00:00 0 b7e65000-b7e88000 r-xp 00000000 08:09 343637 /lib/tls/i686/cmov/libm-2.7.so b7e88000-b7e8a000 rw-p 00023000 08:09 343637 /lib/tls/i686/cmov/libm-2.7.so b7e8a000-b7f72000 r-xp 00000000 08:09 751292 /usr/lib/libstdc++.so.6.0.9 b7f72000-b7f75000 r--p 000e8000 08:09 751292 /usr/lib/libstdc++.so.6.0.9 b7f75000-b7f77000 rw-p 000eb000 08:09 751292 /usr/lib/libstdc++.so.6.0.9 b7f77000-b7f7d000 rw-p b7f77000 00:00 0 b7f8c000-b7f8f000 rw-p b7f8c000 00:00 0 b7f8f000-b7f90000 r-xp b7f8f000 00:00 0 [vdso] b7f90000-b7faa000 r-xp 00000000 08:09 310101 /lib/ld-2.7.so b7faa000-b7fac000 rw-p 00019000 08:09 310101 /lib/ld-2.7.so bfd28000-bfd3d000 rw-p bffeb000 00:00 0 [stack] Aborted

[nanger]

the function definition is as below:

void sort_merge(int* a,int size)
{
  if (size==1) return;
  int middle=size/2;
  int *first =new int[middle];
  int *second =new int[size-middle];
  for(int i=0;i<middle;i++)
  {
    first[i]=a[i];
  }
  
  for(int i=0;i<size-middle;i++)
  {
    second[i]=a[i+middle];
  }  
  
  sort_merge(first,middle); 
  sort_merge(second,size-middle);
  
  int j=0;
  int k=0;
  *(first+middle)=2000000; (used as an INF)
  *(second-middle+size)=200000;
  
  for(int i=0;i<size;i++)
  {
    if(*(first+j)<=*(second+k))
    {
      a[i]=*(first+j);
      j++;
    }
    else
    {
      a[i]=*(second+k);
      k++;
    }
  }
  delete[] first;
  delete[] second;
} 

[helios]

Uhh, you know? You don't need to make a copy of the array to perform a merge sort.
A properly written merge sort can take less than twenty lines.

And what is line 24 supposed to be? You know it's the same as second[size-middle];?

[nanger]

the line 24 is written in this way because it has been allocated a space of size-middle integers

int *second =new int[size-middle];

[nanger]

anyway, before the function returns( line 12 in the main())
sort_merge(b,size);

the array has been sorted in the right order
but when this function returns to the main() domain
the error happens
what is wrong with this?

[dfarmer]

In lines 23 and 24, you appear to be assigning an element that is out of the range of the declared int array (e.g. *(first+middle) = 2000000). Have you tried increasing the size of the allocated arrays by 1?

That is:
int first* = new int[middle+1];
int second* = new int[size-middle+1];

That will make the assignments *(first+middle) = 2000000 and *(second-middle+size) = 2000000 legal. I believe it will also resolve the error you're getting.

[nanger]

In lines 23 and 24, you appear to be assigning an element that is out of the range of the declared int array (e.g. *(first+middle) = 2000000). Have you tried increasing the size of the allocated arrays by 1?

That is:
int first* = new int[middle+1];
int second* = new int[size-middle+1];
____________________________________

It is not neccessary, as I said the sort_merge function finally provided the right ordering
but it just can't return to main()
andn if I allocate one unit more the sort_merge will not be suitabe