Difference between dangling pointer and memory leak

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I don t understand the difference between a dangling pointer and a memory leak  How are these two terms related

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A pointer pointing to a memory location that has been deleted (or freed) is called dangling pointer. There are three different ways where Pointer acts as dangling pointer.

De-allocation of memory

Function Call

Variable goes out of scope

—— from https://www.geeksforgeeks.org/dangling-void-null-wild-pointers/

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Pointer helps to create user defined scope to a variable  which is called Dynamic variable  Dynamic Variable can be single variable or group of variable of same type  array  or group of variable of different types  struct   Default local variable scope starts when control enters into a function and ends when control comes out of that function  Default global vairable scope starts at program execution and ends once program finishes    But scope of a dynamic variable which holds by a pointer can start and end at any point in a program execution  which has to be decided by a programmer  Dangling and memory leak comes into picture only if a programmer doesnt handle the end of scope    Memory leak will occur if a programmer  doesnt write the code  free of pointer  for end of scope for dynamic variables  Any way once program exits complete process memory will be freed  at that time this leaked memory also will get freed  But it will cause a very serious problem for a process which is running long time   Once scope of dynamic variable comes to end freed   NULL should be assigned to pointer variable  Otherwise if the code wrongly accesses it undefined behaviour will happen  So dangling pointer is nothing but a pointer which is pointing a dynamic variable whose scope is already finished

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Dangling Pointer  If any pointer is pointing the memory address of any variable but after some variable has deleted from that memory location while pointer is still pointing such memory location  Such pointer is known as dangling pointer and this problem is known as dangling pointer problem    include lt stdio h gt     int  call       void main           int  ptr        ptr call           fflush stdin         printf   d   ptr           int   call        int x 25       x     return  amp x       Output  Garbage value     Note  In some compiler you may get warning message returning address   of local variable or temporary   Explanation  variable x is local variable  Its scope and lifetime is within the function call hence after returning address of x variable x became dead and pointer is still pointing ptr is still pointing to that location   Solution of this problem  Make the variable x is as static variable  In other word we can say a pointer whose pointing object has been deleted is called dangling pointer   Memory Leak  In computer science  a memory leak occurs when a computer program incorrectly manages memory allocations  As per simple we have allocated the memory and not Free other language term say not release it call memory leak it is fatal to application and unexpected crash

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A dangling pointer is one that has a value  not NULL  which refers to some memory which is not valid for the type of object you expect   For example if you set a pointer to an object then overwrote that memory with something else unrelated or freed the memory if it was dynamically allocated   A memory leak is when you dynamically allocate memory from the heap but never free it  possibly because you lost all references to it   They are related in that they are both situations relating to mismanaged pointers  especially regarding dynamically allocated memory   In one situation  dangling pointer  you have likely freed the memory but tried to reference it afterwards  in the other  memory leak   you have forgotten to free the memory entirely

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A dangling pointer points to memory that has already been freed  The storage is no longer allocated  Trying to access it might cause a Segmentation fault   Common way to end up with a dangling pointer   char  func        char str 10      strcpy str   Hello        return str       returned pointer points to str which has gone out of scope     You are returning an address which was a local variable  which would have gone out of scope by the time control was returned to the calling function   Undefined behaviour   Another common dangling pointer example is an access of a memory location via pointer  after free has been explicitly called on that memory   int  c   malloc sizeof int    free c    c   3    writing to freed location      A memory leak is memory which hasn t been freed  there is no way to access  or free it  now  as there are no ways to get to it anymore   E g  a pointer which was the only reference to a memory location dynamically allocated  and not freed  which points somewhere else now    void func        char  ch   malloc 10       ch not valid outside  no way to access malloc-ed memory   Char-ptr ch is a local variable that goes out of scope at the end of the function  leaking the dynamically allocated 10 bytes

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You can think of these as the opposites of one another   When you free an area of memory  but still keep a pointer to it  that pointer is dangling   char  c   malloc 16   free c   c 1     a     invalid access through dangling pointer    When you lose the pointer  but keep the memory allocated  you have a memory leak   void myfunc         char  c   malloc 16       after myfunc returns  the the memory pointed to by c is not freed  leak

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Memory leak  When there is a memory area in a heap but no variable in the stack pointing to that memory   char  myarea  char   malloc 10    char  newarea  char   malloc 10    myarea newarea    Dangling pointer  When a pointer variable in a stack but no memory in heap   char  p  NULL    A dangling pointer trying to dereference without allocating space will result in a segmentation fault

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A pointer pointing to a memory location that has been deleted (or freed) is called dangling pointer. There are three different ways where Pointer acts as dangling pointer.

De-allocation of memory

Function Call

Variable goes out of scope

—— from https://www.geeksforgeeks.org/dangling-void-null-wild-pointers/

[c] Difference between dangling pointer and memory leak

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