Static array vs dynamic array in C

Question

What is the difference between a static array and a dynamic array in C     I have to do an assignment for my class and it says not to use static arrays  only dynamic arrays  I ve looked in the book and online  but I don t seem to understand    I thought static was created at compile time and dynamic at runtime  but I might be mistaking this with memory allocation     Can you explain the difference between static array and dynamic array in C

User · Accepted Answer

Local arrays are created on the stack  and have automatic storage duration -- you don t need to manually manage memory  but they get destroyed when the function they re in ends  They necessarily have a fixed size   int foo 10     Arrays created with operator new   have dynamic storage duration and are stored on the heap  technically the  free store    They can have any size  but you need to allocate and free them yourself since they re not part of the stack frame   int  foo   new int 10   delete   foo

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Static arrays are allocated memory at compile time and the memory is allocated on the stack  Whereas  the dynamic arrays are allocated memory at the runtime and the memory is allocated from heap      int arr       1  3  4       static integer array     int  arr   new int 3      dynamic integer array

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Static array  Efficiency  No dynamic allocation or deallocation is required    Arrays declared in C  C   in function including  static modifier are static   Example  static int foo 5

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static arrary meens with giving  on  elements in side the array  dynamic arrary meens without giving  on elements in side the array  example        char a 10     static array        char a       dynamic array

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You could have a pseudo dynamic array where the size is set by the user at runtime  but then is fixed after that   int size  cin  gt  gt  size  int dynamicArray size

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I think in this context it means it is static in the sense that the size is fixed  Use std  vector  It has a resize   function

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Yes right the static array is created at the compile time where as the dynamic array is created on the run time  Where as the difference as far is concerned with their memory locations the static are located on the stack and the dynamic are created on the heap  Everything which gets located on heap needs the memory management until and unless garbage collector as in the case of  net framework is present otherwise there is a risk of memory leak

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I think the semantics being used in your class are confusing   What s probably meant by  static  is simply  constant size   and what s probably meant by  dynamic  is  variable size    In that case then  a constant size array might look like this   int x 10     and a  dynamic  one would just be any kind of structure that allows for the underlying storage to be increased or decreased at runtime   Most of the time  the std  vector class from the C   standard library will suffice   Use it like this   std  vector lt int gt  x 10      this starts with 10 elements  but the vector can be resized    std  vector has operator   defined  so you can use it with the same semantics as an array

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Static Array    Static arrays are allocated memory at compile time  Size is fixed  Located in stack memory space  Eg    int array 10      array of size 10  Dynamic Array    Memory is allocated at run time  Size is not fixed  Located in Heap memory space  Eg    int  array   new int 10

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static is a keyword in C and C    so rather than a general descriptive term  static has very specific meaning when applied to a variable or array  To compound the confusion  it has three distinct meanings within separate contexts  Because of this  a static array may be either fixed or dynamic   Let me explain   The first is C   specific    A static class member is a value that is not instantiated with the constructor or deleted with the destructor  This means the member has to be initialized and maintained some other way  static member may be pointers initialized to null and then allocated the first time a constructor is called   Yes  that would be static and dynamic     Two are inherited from C    within a function  a static variable is one whose memory location is preserved between function calls  It is static in that it is initialized only once and retains its value between function calls  use of statics makes a function non-reentrant  i e  not threadsafe  static variables declared outside of functions are global variables that can only be accessed from within the same module  source code file with any other  include s    The question  I think  you meant to ask is what the difference between dynamic arrays and fixed or compile-time arrays  That is an easier question  compile-time arrays are determined in advance  when the program is compiled  and are part of a functions stack frame  They are allocated before the main function runs  dynamic arrays are allocated at runtime with the  new  keyword  or the malloc family from C  and their size is not known in advance  dynamic allocations are not automatically cleaned up until the program stops running

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It s important to have clear definitions of what terms mean  Unfortunately there appears to be multiple definitions of what static and dynamic arrays mean   Static variables are variables defined using static memory allocation  This is a general concept independent of C C    In C C   we can create static variables with global  file  or local scope like this   int x 10     static array with global scope static int y 10     static array with file scope foo         static int z 10     static array with local scope   Automatic variables  are usually implemented using stack-based memory allocation  An automatic array can be created in C C   like this   foo         int w 10     automatic array   What these arrays   x  y  z  and w have in common is that the size for each of them is fixed and is defined at compile time   One of the reasons that it s important to understand the distinction between an automatic array and a static array is that static storage is usually implemented in the data section  or BSS section  of an object file and the compiler can use absolute addresses to access the arrays which is impossible with stack-based storage   What s usually meant by a dynamic array is not one that is resizeable but one implemented using dynamic memory allocation with a fixed size determined at run-time   In C   this is done using the new operator   foo        int  d   new int n     dynamically allocated array with size n        But it s possible to create an automatic array with a fixes size defined at runtime using alloca   foo         int  s    int  alloca n sizeof int     For a true dynamic array one should use something like std  vector in C    or a variable length array in C    What was meant for the assignment in the OP s question   I think it s clear that what was wanted was not a static or automatic array but one that either used dynamic memory allocation using the new operator or a non-fixed sized array using e g  std  vector

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