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cplusplus:pointers_4_slides [2019/03/31 22:24] – mithatcplusplus:pointers_4_slides [2021/10/24 03:02] – [''malloc'' and ''free''] mithat
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 ===== Dynamic memory allocation ===== ===== Dynamic memory allocation =====
   * **Dynamic memory allocation** allows you to reserve blocks of computer memory at //runtime//.   * **Dynamic memory allocation** allows you to reserve blocks of computer memory at //runtime//.
-  * Typically used without associating a variable name with it.+  * Typically used with pointers.
  
 ===== The new operator ===== ===== The new operator =====
-  * ''new <data-type>'' reserves a block of memory to hold the specified %%<data-type>%% and returns the base address of that block:+  * ''new <data-type>'' 
 +    * reserves a block of memory to hold the specified %%<data-type>%% 
 +    * returns the base address of that block. 
 +    * optional parenthesis around ''<data-type>''
  
 <code cpp> <code cpp>
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 </code> </code>
  
-  * ''foo'' points to a ''double'' that is //not// a variable.+  * ''foo'' points to a ''double'' that isn't associated with a variable identifier.
  
 ===== Example ===== ===== Example =====
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     double *myPtr, *yourPtr;     double *myPtr, *yourPtr;
  
-    myPtr = new (double); +    myPtr = new double; 
-    yourPtr = new (double);+    yourPtr = new double;
  
     cout << "Enter a number: ";     cout << "Enter a number: ";
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 void ninetynine() void ninetynine()
 { {
-    int localVar = 99;+    int localVar = 99;  // localVar is destroyed at end of fcn call
     cout << localVar << endl;     cout << localVar << endl;
 } }
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 void ninetynine() void ninetynine()
 { {
-    int *localPtr = new int;+    int *localPtr = nullptr;  // localPtr is destroyed at end of fcn call 
 +    localPtr = new int;       // but not dynamically allocated storage
  
     *localPtr = 99;     *localPtr = 99;
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 ===== Memory leaks ===== ===== Memory leaks =====
  
-  * Memory leaks, no matter how small, are considered bad programming practice. +  * Memory leaks, no matter how small, are bad programming practice. 
-  * They can be fixed by the proper use of **deallocation**:the process of releasing back to the OS storage that was previously dynamically allocated.  +  * Can be fixed by the proper use of **deallocation**: releasing back to the OS storage that was previously dynamically allocated.  
-  * Deallocation of dynamically allocated storage does not happen automatically in C++ +  * **Deallocation of dynamically allocated storage does not happen automatically.** 
-  * You must explicitly (i.e., manually) deallocate the memory.+    * You must explicitly (i.e., manually) deallocate the memory. 
 + 
 +===== The delete operator =====
   * The ''delete'' operator lets you explicitly deallocate memory that has been dynamically allocated.   * The ''delete'' operator lets you explicitly deallocate memory that has been dynamically allocated.
 +
 +<code cpp>
 +int *myPtr = new int;
 +...
 +delete myPtr; // deallocates block pointed to by myPtr.
 +</code>
 +
   * Principle: All dynamically allocated memory must be deallocated somewhere in the program.   * Principle: All dynamically allocated memory must be deallocated somewhere in the program.
-    * "For every ''new'' a ''delete''.+    * "For every ''new'' a ''delete''."
  
 ===== Example ===== ===== Example =====
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 ===== Deallocating arrays ===== ===== Deallocating arrays =====
  
-To deallocate dynamically allocated arrays, use square brackets: ''delete [] arrayPtr;''+Use square brackets to deallocate dynamically allocated arrays: ''delete [] arrayPtr;''
  
 <file cpp Gaddis-Pr9-14.cpp> <file cpp Gaddis-Pr9-14.cpp>
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 int main() int main()
 { {
-    double *sales = nullptr, // To dynamically allocate an array +    double *sales = nullptr,    // To dynamically allocate an array 
-    total = 0.0, // Accumulator +    total = 0.0,                // Accumulator 
-    average; // To hold average sales +    average;                    // To hold average sales 
-    int numDays, // To hold the number of days of sales +    int numDays,                // To hold the number of days of sales 
-        count; // Counter variable+        count;                  // Counter variable
  
     // Get the number of days of sales.     // Get the number of days of sales.
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 ===== heap vs. stack ===== ===== heap vs. stack =====
  
-  * Local variables and dynamically allocated storage come from different pools of RAM.+  * Local variables and dynamically allocated storage come from pools of RAM.
   * **stack**: a pool of memory whose allocation and deallocation is automatically managed.   * **stack**: a pool of memory whose allocation and deallocation is automatically managed.
     * Local and global variables are allocated from the stack.     * Local and global variables are allocated from the stack.
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   * ''malloc'' and ''free'' can also used be used to allocate and deallocate storage.   * ''malloc'' and ''free'' can also used be used to allocate and deallocate storage.
   * Part of C and so are available in C++ as well.   * Part of C and so are available in C++ as well.
-  * More cumbersome than ''new'' and ''delete'', and their use is discouraged.+  * More cumbersome than ''new'' and ''delete'', so their use is discouraged.
  
 ===== Returning Pointers from Functions ===== ===== Returning Pointers from Functions =====
cplusplus/pointers_4_slides.txt · Last modified: 2021/10/24 03:02 by mithat
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