An uninitialized variable/pointer becomes a definition or a declaration?

Question

Suppose I have the following program:

int main(void)
{
int i; //Line 1
i=5;  //Line 2

int *j; //line 3
j=&i; //line 4
}

If I try to print i after line 1 in Visual Studio, it gives me a compile time error saying unitialized variable i used. Does this mean that no storage was allocated to i and line 1 is only a declaration? I understand line 2 is a definition.

Also, what about line 3 and line 4? Are they declarations or definitions?

Storage is allocated but value not assigned is declaration or definition? — user2684198, Jul 15 '14 at 06:51
In gcc, it prints garbage values. Does not throw compile time error — Yusuf Husainy, Jul 15 '14 at 06:51
Have a look at [difference-between-a-definition-and-a-declaration](http://stackoverflow.com/questions/1410563/what-is-the-difference-between-a-definition-and-a-declaration). — Dayal rai, Jul 15 '14 at 06:52
@user2684198 in defination. Also printing it leads [Undefined Behavior.](http://stackoverflow.com/questions/6824488/is-uninitialized-data-behavior-well-specified) — Jayesh Bhoi, Jul 15 '14 at 06:52
Line 2 is an assignment, not a definition. Line 1 is a definition. — Wyzard, Jul 15 '14 at 06:53

score 5 · Accepted Answer · answered Jul 15 '14 at 06:57

Line 1 and Line 3 are definitions, It's also legal to say they are declarations because all definitions are declarations.

The error is because using uninitialized variables is undefined behavior, not because their storage are not allocated.

Line 2 and Line 4 are assignment statements. You seem to be confused with initalization and assignment.

int n = 42; //definition with initalization
int m;      //definition, but uninitiazlied
n = 10;     //assignment
m = 10;     //assignment

An uninitialized variable/pointer becomes a definition or a declaration?

1 Answers1