Dear members, can any one tell me what exactly meaning of:- Variable constant( const <data type> variable_name); pointer to a constant constant pointer
constant variable say const int a=10; then u cant change a to any other value... ie., a=11; would be an error.. constant pointer int i=10,j; int *const a=&i; then that pointer is a constant pointer to that memory location..so that pointer can't be used to point to other location... a=&j; //would be an error pointer to a constant int i=10; const int *p=&i; then the value pointed to by the pointer cant be changed. *p=11; would be an error..
dear IndiraP, i agree with u what u are saying about constant variable, but i get confused when i access constant variable through a pointer, it not only allow me to access the value but through this i can also modify the value of constant variable. main() { const int a=10; a=11; // generates error int *ptr; ptr =&a; *ptr =11; printf("\n Now value of constant variable a is : %d",a); getch(); return 0; } plz tell me how variable a become constant.
see...wat do u mean by constant variable first of all??? u r actually making a variable hold a constant value in it instead of allowing it to handle multiple varibale values..rite..??? now in the program u mentioned..u made "a" variable constant..means "a" can only hold 10...so it can't take any other value not even 11..!!! n when u created a pointer for it...look carefully...u created a pointer to "a" which is constant n which holds only 10 ..rite??? it means.. a pointer to a constant...so wat happens..even the pointer can't change the value that it is pointing to...afterall "a"-->can only hold 10....n when u r manipulating *p..u r actually trying to change "a'"s value ..so will it allow.??? no ...rite?? n "a" is nothing but the name of the memory location where 10 resides...so p=&a..makes p point to the memory location of "a"...n *p is value at &a...where that memory is locked to hold only 10 by specifying it constant...so *p=11 is error.. n refer to pointer to constant..for any better understanding.. got it???
Dear Indira P I got u and also agree with u but first copy the below program and run then see what i am asking:- Code: #include<stdio.h> #include<conio.h> int main() { const int a=10; int *ptr; ptr=&a; printf("\n Now the value at memory : %u is : %d ",&a,a); *ptr=11; printf("\n Now the value at memory : %u is : %d ",&a,a); getch(); return 0 ; }
yeah..i did run it..n u get error at p=&a; stating that "const int * can't be converted into int * " rite???.. it's because...tha variable is constant...so the pointer that it points to becomes pointer to a constant..rite??? but *p is declared as normal integer...so in order to eliminate the error make *p a const int *p; and coming to *p=11...u can't change the value anyway..!!!
