Winter2015 COMP 2130 Intro Computer Systems Computing Science
Thompson Rivers University C: Advanced Topics
Slide 2
Unit Learning Objectives TRU-COMP2130 C: Advanced Topics 2 Use
pointers for dynamic memory management. Structures and unions Use
open(), read(), write(), close(), and FILE* functions to manipulate
files. Use user-defined data structures. More coming
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Unit Contents TRU-COMP2130 C: Advanced Topics 3 1. Pointers and
Arrays 2. Input and Output 3. Structures 4. Self Referential
structures
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TRU-COMP2130 C Programming 4 Dynamic memory management #include
void *malloc(int size); // allocate size bytes // and return the
addr void free(void *); // free the memory space... int *p, n;
scanf(%d, &n); // space for n-many integer variables. p =
(int*)malloc(sizeof(int) * n); p[0] = 10; *(p+1) = 20; *(p+2) = 30;
p++; *p = 4;
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Structures Introduction 5 It is a way to have a single name
referring to a group of a related values. Structures provide a way
of storing many different values in variables of potentially
different types under the same name. its design makes things more
compact. Structs are generally useful whenever a lot of data needs
to be grouped together Example: a contact group may have {name,
address, phone number, and mobile number} TRU-COMP2130
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Example Introduction 6 struct database { int id_number; int
age; float salary; }; int main() { struct database employee; /*
There is now an employee variable that has modifiable variables
inside it.*/ employee.age = 22; employee.id_number = 1;
employee.salary = 12000.21; printf(Employee ID = %d, Age = %d and
Salary = %7.2f, employee.id, employee.age, employee.salary); }
TRU-COMP2130
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2. Structures TRU-COMP2130 C: Advanced Topics 7 User-defined
data structure struct student_rcd {// class without methods in Java
intstudent_number; charname[128];... };... struct student_rcd
record[10], *rp; struct student_rcd test;// how to declare a struct
variable test.student_number = 10;// how to access a member
print_rcd(test); read_rcd(&test); record[0].student_number =
5;
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TRU-COMP2130 C: Advanced Topics 8 void print_rcd(struct
student_rcd rcd) { printf(Number: %d\n, rcd.student_number);
printf(Name: %s\n, rcd.name); // name is an array. // not
&(rcd.name) } void read_rcd(struct student_rcd *rcd) {
printf(Enter number: ); scanf(%d, &(rcd->student_number));
// reference rqd printf(Enter name: ); scanf(%s, rcd->name); //
name is an array. // not &(rcd->name) }
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Typedef TRU-COMP2130 C: Advanced Topics 9 typedef int Length;
// Now Length is a data type. typedef char *String; // Now String
is a data type. typedef struct tnode { /* the tree node: */ char
*word; /* points to the text */ int count; /* number of occurrences
*/ struct tnode *left, *right; /* children */ struct tnode *parent;
} Treenode; // Now Treenode is a data type.... Length len, maxlen;
Length *lengths[]; String p, lineptr[MAXLINES];
Treenodetnode1;
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Union TRU-COMP2130 10 A union is a special data type available
in C that enables you to store different data types in the same
memory location like structures The main difference is that a union
may have many members, but only one member can contain a value at
any given time. Unions provide an efficient way of using the same
memory location for multi-purpose. #include union Data { int i;
float f; char str[20]; }; int main( ) { union Data data; data.i =
10; printf( "data.i : %d\n", data.i); return 0; }
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Self-Referential Structures TRU-COMP2130 C: Advanced Topics 11
struct tnode { /* the tree node: */ char word[50]; int count;
struct tnode *next; /* next child */ }; struct tnode root;
root.next = (struct tnode *)malloc(...);
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Dynamic Memory Allocation TRU-COMP2130 C: Advanced Topics 12
struct Student { char name[128]; int number; Student *next; };
typedef struct Student Student; Student *head = null; // important
Student *new, *tmp; new = create_student(); // create a record,
read data from the user, // store them into the record
add_student(head, new); // add the new record at the end of the
list tmp = find_student(head, 968374); // find the record whose
number is.. printf(%d: %s\n, tmp->number, tmp->name); //
print the record delete_student(head, 968374); Name Number next
Name Number next Name Number next Head null
Malloc() TRU-COMP2130 Introduction 14 The name malloc stands
for "memory allocation". The function malloc() reserves a block of
memory of specified size and return a pointer of type void which
can be casted into pointer of any form. Syntax of malloc()
ptr=(cast-type*)malloc(byte-size) ptr is pointer of cast-type. The
malloc() function returns a pointer to an area of memory with size
of byte size. If the space is insufficient, allocation fails and
returns NULL pointer. Example: ptr=(int*)malloc(100*sizeof(int));
will allocate either 200 or 400 according to size of int 2 or 4
bytes respectively and the pointer points to the address of first
byte of memory.
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Calloc() TRU-COMP2130 Introduction 15 The name calloc stands
for "contiguous allocation". The only difference between malloc()
and calloc() is that, malloc() allocates single block of memory
whereas calloc() allocates multiple blocks of memory each of same
size and sets all bytes to zero. Syntax of calloc()
ptr=(cast-type*)calloc(n,element-size); This statement will
allocate contiguous space in memory for an array of n elements.
Example: ptr=(float*)calloc(25,sizeof(float)); This statement
allocates contiguous space in memory for an array of 25 elements
each of size of float, i.e, 4 bytes.
Slide 16
Free() TRU-COMP2130 Introduction 16 Dynamically allocated
memory with either calloc() or malloc() does not get return on its
own. The programmer must use free() explicitly to release space.
syntax of free() free(ptr); This statement cause the space in
memory pointer by ptr to be deallocated.
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realloc TRU-COMP2130 Introduction 17 If the previously
allocated memory is insufficient or more than sufficient. Then, you
can change memory size previously allocated using realloc(). Syntax
of realloc() ptr=realloc(ptr,newsize); Here, ptr is reallocated
with size of newsize.
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TRU-COMP2130 C: Advanced Topics 18... create_student(... ) //
create a record, read data from the user, { // store them into the
record Student *new = (... )malloc(... ); scanf(%s,...) // read
name scanf(%d,...) // read number new->next = null; // very
important; (*new).next = null return...; };... add_student(...
head,... new) // add the new record at the end of the list {
Student *tmp; if (head == null) // when there is no record yet head
= new; else { while((*tmp).next != null) // move to the last record
tmp = (*tmp).next; // You cannot use array syntaxes (*tmp).next =
new; // because the Student objects were not } // consecutively
created. return; }
