Do I need to initialize my variables to a default value?

Question

When creating a file pointer should I initialize it to NULL or should I leave it uninitialized?

I currently have FILE* img;. I think the better practice is to have FILE* img = NULL; so it it doesn't store a garbage value. However, I seem to get an error when doing this.

Any thoughts?

EDIT

FILE* img;    

while (fread(&buffer, BLOCK, 1, inptr) != 0) 
{
    // do stuff
    if (beginning of file)
    {
        img = fopen(title, "a");
    }
}
fclose(img);

Answer 1

I always prefer doing what I need to do. no more and no less. for example

int i;

if (condition)
    i = 10;
else
    i = 20;

I wouldn't bother unnecessarily initialize i here, assuming condition does not involve i of course, since it's initialized anyway in either the if or the else branch.

on the other hand,

int i = 10;

for (int j = 0; j < 5; j++)
    i += 2;

I indeed would initialize i here since not initializing it could cause problems.

so the answer to your question is: if you want your variable to have a certain value at some point, then have this value assigned to it so that it has it at this point.