0xC0000005 Access violation reading location 0x00000000

Question

I m having a very strange issue with a space invaders game I m working on  Basically I get an access violation error      Unhandled exception at 0x5edad442  msvcr100d dll  in   SpaceInvaders exe  0xC0000005  Access violation reading location   0x00000000    when I include the piece of code below   visual studio takes me to  strcmp asm  when debugging  Note that Im not using strcmp   in any of my code  Is there anything wrong with the code  or is this a problem beyond the scope of what I ve included  Thanks for any help  const char  invarray       invader0 png    invader1 png    invader2 png    invader3 png    invader4 png     int i 0    Creates 55 invaders for  int y 0  y lt 250  y  50       for  int x 0  x lt 550 x  50           Invader inv invarray y 50   x 50  y 550  15  15  1  false  250           invaders i    inv            Invader constructor   Invader  Invader const char  pic  int x  int y  int w  int h  bool dir  bool des  int point    MovingObject pic  x  y  w  h    direction dir   destroyed des   b 0   points point       MovingObject Constructor  MovingObject  MovingObject const char  pic  int x  int y  int w  int h  picture pic   positionX x   positionY y   width w   height h

User · Accepted Answer

This line looks suspicious   invaders i    inv    You re never incrementing i  so you keep assigning to invaders 0    If this is just an error you made when reducing your code to the example  check how you calculate i in the real code  you could be exceeding the size of invaders   If as your comment suggests  you re creating 55 invaders  then check that invaders has been initialised correctly to handle this number

User · Answer

Access violation reading location 0x00000000  means that you re derefrencing a pointer that hasn t been initialized and therefore has garbage values  Those garbage values could be anything  but usually it happens to be 0 and so you try to read from the memory address 0x0  which the operating system detects and prevents you from doing   Check and make sure that the array invaders   is what you think it should be    Also  you don t seem to be updating i ever - meaning that you keep placing the same Invader object into location 0 of invaders   at every loop iteration

User · Answer

The problem here  as explained in other comments  is that the pointer is being dereference without being properly initialized  Operating systems like Linux keep the lowest addresses  eg first 32MB  0x00 0000 -0x200 0000  out of the virtual address space of a process  This is done because dereferencing zeroed non-initialized pointers is a common mistake  like in this case  So when this type of mistake happens  instead of actually reading a random variable that happens to be at address 0x0  but not the memory address the pointer would be intended for if initialized properly   the pointer would be reading from a memory address outside of the process s virtual address space  This causes a page fault  which results in a segmentation fault  and a signal is sent to the process to kill it  That s why you are getting the access violation error

[c++] 0xC0000005: Access violation reading location 0x00000000

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