Memory Management in C Memory Management in C Personal Software - PowerPoint PPT Presentation

Memory Management in C Memory Management in C Personal Software Engineering Personal Software Engineering

Memory Organization Memory Organization  The call stack grows from the The call stack grows from the Function Call The top of memory down top of memory down Stack Frames  Code is at the bottom of Code is at the bottom of sp memory. memory.  Global data follows the code. Global data follows the code. Available The for  What's left What's left – the "heap" the "heap" - is is Heap allocation available for allocation. available for allocation. Global Variables Binary Code 0

Allocating Memory Allocating Memory void *malloc( unsigned nbytes ) ; void *malloc( unsigned nbytes ) ; – Allocates 'nbytes' of memory in the heap. Allocates 'nbytes' of memory in the heap. – Guaranteed not to overlap other allocated memory. Guaranteed not to overlap other allocated memory. – Returns pointer to the first byte (or NULL if the heap is full). Returns pointer to the first byte (or NULL if the heap is full). – Similar to constructor in Java Similar to constructor in Java – allocates space. allocates space. – Space allocated uninitialized (random garbage). Space allocated uninitialized (random garbage). void free( void *ptr ) ; void free( void *ptr ) ; – Frees the memory assigned to ptr. Frees the memory assigned to ptr. – The space must have been allocated by malloc. The space must have been allocated by malloc. – No garbage collection in C (or C++). No garbage collection in C (or C++). – Can slowly consume memory if not careful Can slowly consume memory if not careful

How Much Space Is Needed? How Much Space Is Needed? - 1 1 sizeof sizeof ( type type ) ) – – gives the size of a type in bytes. gives the size of a type in bytes. Allocation Examples Allocation Examples ip int int *ip ip ; ????

How Much Space Is Needed? How Much Space Is Needed? - 1 1 sizeof sizeof ( type type ) ) – – gives the size of a type in bytes. gives the size of a type in bytes. Allocation Examples Allocation Examples ip int int *ip ip ; ???? ip ???? ip = ip = (int int *) *) malloc malloc( ( sizeof sizeof(int int) ) ) ) ;

How Much Space Is Needed? How Much Space Is Needed? - 1 1 sizeof sizeof ( type type ) ) – – gives the size of a type in bytes. gives the size of a type in bytes. Allocation Examples Allocation Examples ip int *ip int ip ; ???? ip ???? ip ip = = (int int *) *) malloc malloc( ( sizeof sizeof(int int) ) ) ) ; ip 1234 *ip ip = 1234 ; = 1234 ;

How Much Space Is Needed? How Much Space Is Needed? - 1 1 sizeof sizeof ( type type ) ) – – gives the size of a type in bytes. gives the size of a type in bytes. Allocation Examples Allocation Examples ip int int *ip ip ; ???? ip ???? ip = ip = (int int *) *) malloc malloc( ( sizeof sizeof(int int) ) ) ) ; ip 1234 *ip ip = 1234 ; = 1234 ; ip ip = ( = (int int *) *)malloc malloc( ( sizeof sizeof(int int) ) ; ) ) ; ip 1234 ????

How Much Space Is Needed? How Much Space Is Needed? - 1 1 sizeof sizeof ( type type ) ) – – gives the size of a type in bytes. gives the size of a type in bytes. Allocation Examples Allocation Examples ip int int *ip ip ; ???? ip ???? ip = ip = (int int *) *) malloc malloc( ( sizeof sizeof(int int) ) ) ) ; ip 1234 *ip ip = 1234 ; = 1234 ; orphan storage ip = ( ip = (int int *) *)malloc malloc( ( sizeof sizeof(int int) ) ; ) ) ; ip 1234 ????

How Much Space Is Needed? How Much Space Is Needed? - 1 1 sizeof sizeof ( type type ) ) – – gives the size of a type in bytes. gives the size of a type in bytes. Allocation Examples Allocation Examples ip int *ip int ip ; ???? ip ???? ip ip = = (int int *) *) malloc malloc( ( sizeof sizeof(int int) ) ) ) ; ip 1234 *ip ip = 1234 ; = 1234 ; ip free( free(ip ip) ; ) ; ???? 1234

How Much Space Is Needed? How Much Space Is Needed? - 1 1 sizeof sizeof ( type type ) ) – – gives the size of a type in bytes. gives the size of a type in bytes. Allocation Examples Allocation Examples ip int int *ip ip ; ???? ip ???? ip ip = = (int int *) *) malloc malloc( ( sizeof sizeof(int int) ) ) ) ; ip 1234 *ip ip = 1234 ; = 1234 ; ip free(ip free( ip) ; ) ; ???? 1234 ip ip = ( = (int int *) *)malloc malloc( ( sizeof sizeof(int int) ) ; ) ) ; ip ????

How Much Space Is Needed? How Much Space Is Needed? - 2 2 char * char *make_copy make_copy( char * ( char *orig orig ) { ) { char *copy = (char *) char *copy = (char *) malloc malloc( ( sizeof sizeof(char) * (char) * strlen strlen(orig orig) + 1 ) ; ) + 1 ) ; (void) (void) strcpy strcpy( copy, ( copy, orig orig ) ; ) ; return copy ; return copy ; } char *copy char orig[4] ; 'J' 'o' 'e' '\0' 'J' 'o' 'e' '\0' char **create_string_vector char ** create_string_vector( ( int int nstrings nstrings ) { ) { char ** char **str_vector str_vector ; str_vector str_vector = (char **) = (char **) malloc malloc( ( nstrings nstrings * * sizeof sizeof(char *) ) ; (char *) ) ; return return str_vector str_vector ; } nstrings nstrings str_vector str_vector

Linked Lists Linked Lists  Structures with values and link (pointer) to next Structures with values and link (pointer) to next – and and  possibly previous possibly previous - structure. structure.  Example: List of strings: Example: List of strings:  typedef struct node { top string "New Years" next char *string ; struct node *next ; } node ; string "4th of July" next node *top ; string "Labor Day" next