CODEWITHSUNDEEP
c++
AvinashK
AvinashK

Reputation: 3423

pointer arithmetic

//if the following code works  
char *ptr=a+12;  
//why doesnt this work  
char *(ptr=a+12);

Upvotes: 2

Views: 145

Answers (6)

Armen Tsirunyan
Armen Tsirunyan

Reputation: 133112

because char *ptr=a+12; is a declaration with an initializer and char *(ptr=a+12); is ... well, nothing.

But this will work.

char* ptr;
ptr = a+12;
char x = *(ptr = a+12);

Upvotes: 2

Lightness Races in Orbit
Lightness Races in Orbit

Reputation: 385385

char* ptr = a + 12; declares and defines a pointer-to-char to point 12 characters after a does.

char* (ptr = a + 12); tries to assign the value (a + 12) to the pointer ptr, and then dereference it to produce a value. However Type value is not valid syntax (like int 0; or char 'x'; are not valid), and ptr is never declared/defined.

In short, it's completely senseless.

Upvotes: 0

Mahesh
Mahesh

Reputation: 34655

() has a higher priority. So, the expression in it evaluates first and is not a valid lvalue to assign to.

Upvotes: 0

Tom Macdonald
Tom Macdonald

Reputation: 6593

Because you are declaring as a pointer a whole expression, which makes no sense. A pointer must be a variable.

Upvotes: 0

Erik
Erik

Reputation: 91320

char * ptr; declares a variable, =a+12 gives it a value. What you're doing makes no sense, the variable must exist in order for a value to be assigned. What are you trying to achieve?

This would be valid.

char * foo;
char * ptr = (foo = a + 12);

Upvotes: 0

Jon
Jon

Reputation: 437804

Because (ptr=a+12) is not a valid name for a variable. What are you trying to achieve exactly?

Upvotes: 2

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