Why is the following code valid for a char pointer but not for a int pointer?
I am confused as to why I cant use the same approach for both.
But this will failCode:char *y; y = “This is great”; printf(“%s”, y);
Code:int *x; x = 25; printf(“%d”, x);
%s expects a pointer to char
%d expects an int
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
Because %s expects a char pointer, which is what y is.
%d expects an int.
int x = 42;
int *px = &x;
*px = 21;
printf( "%d", *px );
Dereferencing a pointer to an int gets an int, which is what %d needs.
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
I was really messed up on that but it makes more sense now. This learn C in 21 days book is not all that detailed. Anyways I can see now the difference lies in %s and %d so thanks.
So both of these are legal ways to assign values to a pointer?
y = “This is great”;
x = 25;
and I just was wrong in the manner I tried to use printf as you stated?
No, but the first one is fine.
If x is defined as an int *, then you are assigning an address of 25 to x, not the value of 25.
If you want to point to the address of the 25, then do this:
int * x ;
int n = 25 ;
x = &n ;
Now, x point to the address of an int.
Mainframe assembler programmer by trade. C coder when I can.
Is the below true then?
p is the pointer
sorry bout the uppercase
WHEN USING CHAR POINTERS
P = ENTIRE STRING
&P = ADDRESS OF THE POINTER
*P = 1RST BLOCK OF THE STRING
*(P + 2) = 3RD BLOCK OF THE STRING
WHEN USING INT POINTERS
P = ADDRESS OF THE CONTENTS P IS POINTING TO
&P = ADDRESS OF THE POINTER ITSELF (INT *P's ADDRESS)
*P = CONTENTS OF THE POINTER (1 BLOCK OF MEMORY)
THE POINTER MUST BE INITIALIZED AND VALUES ASSIGNED
IN A MANNER SUCH AS BELOW:
int time = 500;
int *carl2;
carl2 = &time;
Last edited by cjohnman; 05-02-2008 at 01:03 PM.
char and int pointer are very close - they just differ in "block" size
for char pointer it is sizeof(char) = 1 byte
for int pointer it is sizeof(int)
as additional benefit sequence of chars with nul-terminating char is processed as a C-string by standard library functions desined to process the C-strings
there is no such assumption for sequense of ints...
All problems in computer science can be solved by another level of indirection,
except for the problem of too many layers of indirection.
– David J. Wheeler
