Check array position for null empty

Question

I have an array which might contain empty null positions  e g  array 2  3  array 4  empty unassigned   I want to check in a loop whether the array position is null    array 4   NULL   this doesn t work   I m pretty new to C    Thanks    Edit  Here s more code  A header file contains the following declaration  int y 50     The population of the array is done in another class   geoGraph y x    nums x     The array should be checked for null in the following code       int x 0      for int i 0  i lt sizeof y  i               check for null         p i  SetPoint Recto Height  -x y i            if i gt 0               dc MoveTo p i-1                dc LineTo p i                       x  50

User · Answer

If the array contains integers  the value cannot be NULL  NULL can be used if the array contains pointers   SomeClass  myArray 2   myArray 0    new SomeClass    myArray 1    NULL   if  myArray 0     NULL       this will be executed   if  myArray 1     NULL       this will NOT be executed     As http   en cppreference com w cpp types NULL states  NULL is a null pointer constant

User · Answer

If your array is not initialized then it contains randoms values and cannot be checked    To initialize your array with 0 values   int array 5     0     Then you can check if the value is 0   array 4     0    When you compare to NULL  it compares to 0 as the NULL is defined as integer value 0 or 0L   If you have an array of pointers  better use the nullptr value to check   char  array 5     nullptr      we defined an array of char   initialized to nullptr  if  array 4     nullptr         do something

User · Answer

You can use boost  optional  or std  optional for newer versions   which was developed in particular for decision of your problem   boost  optional lt int gt  y 50        geoGraph y x    nums x        const size t size y   sizeof y  sizeof y 0           correct size of y     for int i 0  i lt size y i        if y i       check for null       p i  SetPoint Recto Height  -x  y i                        P S  Do not use C-type array -  use std  array or std  vector   std  array lt int  50 gt  y      not int y 50

User · Answer

There is no bound checking in array in C programming  If you declare array as   int arr 50     Then you can even write as   arr 51    10    The compiler would not throw an error  Hope this answers your question

[c++] Check array position for null/empty

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