CODEWITHSUNDEEP
cstaticinitialization
yCalleecharan
yCalleecharan

Reputation: 4704

C static variables and initialization

If I have a global static variable x like in this code

 #include <stdio.h>
 #include <stdio.h>

 static int x;

 int main(void)
 {

 DO SOMETHING WITH x HERE

 x++;

 }

What will be difference if I opted to initialize x to a value first say as in 

static int x = 0;

before entering "main"?

In my first case where I didn't assign a value to x, does the compiler implicitly know that x is to be set to zero as it's a static variable? I heard that we can do this with static variables.

Thanks a lot...

Upvotes: 5

Views: 8622

Answers (4)

Smalcat
Smalcat

Reputation: 231

There is a nice answer here:

Just a short excerpt:

First of all in ISO C (ANSI C), all static and global variables must be initialized before the program starts. If the programmer didn't do this explicitly, then the compiler must set them to zero. If the compiler doesn't do this, it doesn't follow ISO C. Exactly how the variables are initialized is however unspecified by the standard.

Upvotes: 5

Arkku
Arkku

Reputation: 42109

static variables are automatically initialised to zero (i.e. as though you had assigned zero to them, causing floats and pointers to become 0.0 and NULL, respectively, even if the internal representation of those values is not all bits zero).

Upvotes: 3

Lance Richardson
Lance Richardson

Reputation: 4620

Static variables are always implicitly initialized to zero, so there would be no difference in explicitly initializing x to zero.

Upvotes: 0

kennytm
kennytm

Reputation: 523184

Static variables with explicit initialization are always initialized to zero (or null-pointer, depending on the type). The C standard §6.7.8/10 has description on this. But explicitly setting it to 0 can help others no need to wonder about the same question :).

Upvotes: 8

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