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Pointers,Command Line & Dynamic memory allocation
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Pointers,Command Line & Dynamic memory allocation
JELLYCORN
12-2-2021
POINTERS
AGENDA
- Pointers
- Pointers to pointers
- Pointer Arithmetic
- Dangling Pointer
- Function Pointer
AGENDA
C Pointers
The pointer in C language is a variable which stores the address of another variable. This variable can be of type int, char, array, function, or any other pointer. The size of the pointer depends on the architecture. However, in 32-bit architecture the size of a pointer is 2 byte.
POINTERS
Declaring a pointer
The pointer in c language can be declared using * (asterisk symbol). It is also known as indirection pointer used to dereference a pointer.
int *a;//pointer to int
char *c;//pointer to char
Declaring a pointer
example
#include<stdio.h>
int main(){
int number=50;
int *p;
p=&number;//stores the address of number variable
printf("Address of p variable is %x \n",p); // p contains the address of the number therefore printing p gives the address of number.
printf("Value of p variable is %d \n",*p); // As we know that * is used to dereference a pointer therefore if we print *p, we will get the value stored at the address contained by p.
return 0;
}
POINTERS
Advantage of pointer
1) Pointer reduces the code and improves the performance, it is used to retrieving strings, trees, etc. and used with arrays, structures, and functions.
2) We can return multiple values from a function using the pointer.
3) It makes you able to access any memory location in the computer's memory.
USAGE OF POINTER
POINTERS
There are many applications of pointers in c language.
1) Dynamic memory allocation
In c language, we can dynamically allocate memory using malloc() and calloc() functions where the pointer is used.
2) Arrays, Functions, and Structures
Pointers in c language are widely used in arrays, functions, and structures. It reduces the code and improves the performance
PLACEMENT
POINTERS
https://www.indiabix.com/c-programming/pointers/
https://www.geeksforgeeks.org/c-language-2-gq/pointers-gq/
Double pointer
or
pointer to pointer
https://www.youtube.com/watch?v=Wjhbt3ICbJg
POINTERS
Pointer Arithmetic
Pointer
Arithmetic
We can perform arithmetic operations on the pointers like addition, subtraction, etc. However, as we know that pointer contains the address, the result of an arithmetic operation performed on the pointer will also be a pointer if the other operand is of type integer. In pointer-from-pointer subtraction, the result will be an integer value. Following arithmetic operations are possible on the pointer in C language:
- Increment
- Decrement
- Addition
- Subtraction
- Comparison
Dangling Pointer
Dangling
Pointer
Dangling
Pointer
Dangling
Pointer
Function pointer
we can also create a pointer pointing to a function. The code of a function always resides in memory, which means that the function has some address. We can get the address of memory by using the function pointer.
Function
pointer
Example
Example
#include <stdio.h>
int main()
{
printf("Address of main() function is %p",main);
return 0;
}
Command Line Arguments
The arguments passed from command line are called command line arguments. These arguments are handled by main() function.
To support command line argument, you need to change the structure of main() function as given below.
int main(int argc, char *argv[] )
- Here, argc counts the number of arguments. It counts the file name as the first argument.
- The argv[] contains the total number of arguments. The first argument is the file name always.
Command
Line
Arguments
Example
Example
#include <stdio.h>
void main(int argc, char *argv[] ) {
printf("Program name is: %s\n", argv[0]);
if(argc < 2){
printf("No argument passed through command line.\n");
}
else{
printf("First argument is: %s\n", argv[1]);
}
}
OUTPUT
Run this program as follows in Linux:
---------------------------------------------------
./program hello
---------------------------------------------------
Run this program as follows in Windows from command line:
program.exe hello
-----------------------------------------------------
Output:
Program name is: program
First argument is: hello
If you pass many arguments, it will print only one.
------------------------------------------------------
./program hello c how r u
Output:
Program name is: program
First argument is: hello
But if you pass many arguments within double quote, all arguments will be treated as a single argument only.
--------------------------------------------------------
./program "hello c how r u"
Output:
Program name is: program
First argument is: hello c how r u
Dynamic
Memory
Allocation
The concept of dynamic memory allocation in c language enables the C programmer to allocate memory at runtime. Dynamic memory allocation in c language is possible by 4 functions of stdlib.h header file.
- malloc()
- calloc()
- realloc()
- free()