Do I really need to zero arrays?

[John Smith]

I have a two dimentional char array. Before filling it using
strtok(), I reset its elements to '\0' using two nested for loops.
The code works as I hope it would but I wonder whether I really
need to reset the array. The program would run faster if I don't
need to reset.

------------------------------------------
int Array(void)

.................
for(i=0; i<ArrayNo; i++)
for(j=0; j<ArraySize; j++)
Arrays[j]='\0';


pch = strtok (buffer,"\n");
while (pch != NULL)
{
strcpy(Arrays[ii],pch);
ii++;
pch = strtok (NULL, "\n");
}
...............
------------------------------------------

 

[Peter Nilsson]

I have a two dimentional char array. Before filling it using
strtok(), I reset its elements to '\0' using two nested for
loops.
The code works as I hope it would but I wonder whether I really
need to reset the array. The program would run faster if I don't
need to reset.

------------------------------------------
int Array(void)

................
for(i=0; i<ArrayNo; i++)
for(j=0; j<ArraySize; j++)
Arrays[j]='\0';

Your strcpy will properly copy the string (which by definition
includes a null byte,) however any array elements that do not
receive a string will have unspecified, assuming Arrays is a
non-initialised block scope object.

As an aside, you can zero initialise an object more easily...

char Arrays[X][Y] = { { 0 } };

With such a declaration, you could also use memset to re-
initialise it...

memset(Arrays, 0, sizeof Arrays);

pch = strtok (buffer,"\n");
while (pch != NULL)
{
strcpy(Arrays[ii],pch);

You should be careful that there is actually space for the string
in your arrays.