How to set all the elements of array to 0, after initialization or 2nd time in a loop?

Question

I am stuck with basics of an array. I googled it, but I could not able to solve this. This question is concept oriented, but I am not able to bridge a gap. Please help me out resolve this.

I am very clear on initializing array for the first time, but not able to clear the array for next time :-( :-(

int myArray[10] = { 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 }; // All elements of myArray are 5
int myArray[10] = { 0 };    // Will initialize all elements to 0
int myArray[10] = { 5 };    // Will initialize myArray[0] to 5 and other elements to 0
static int myArray[10]; // Will initialize all elements to 0

int myArray[10];// This will declare and define (allocate memory) but won’t initialize
int i;  // Loop variable
for (i = 0; i < 10; ++i) // Using for loop we are initializing
{
    myArray[i] = 5;
}

Problem statement:

I am using a Global array which is of size 10000. I have 1k iteration loop, where I have to set the array to 'Zero' or predefined value i.e., 5 for each iteration.

I am doing this at the end of interaction like this:

myArray[10000] = { 0 };

Its giving error while compiling in GCC compiler.

error: [11707] syntax error before '{' token

Please help me out resolve this.

Thanks in advance.

Isn't memset() for you? ... memset() won't able to set each values to 5. — MikeCAT
– MikeCAT, Commented May 8, 2016 at 14:43
memset, loop with incementing index or pointer, bzero... . maybe you should just move to a different course? — Martin James
– Martin James, Commented May 8, 2016 at 14:44
@ Martin, I can't use Memset, because od some constraint. Is there any other way to achieve this? — Jon S
– Jon S, Commented May 8, 2016 at 14:46
I really don't understand, y this down votes. Is anyone can explain? — Jon S
– Jon S, Commented May 8, 2016 at 14:48
If you're re-initializing your array on each iteration, you may as well declare the array inside the loop. — Oliver Charlesworth
– Oliver Charlesworth, Commented May 8, 2016 at 14:50

totoro · Accepted Answer · 2016-05-08 15:27:28Z

4

myArray[10000] = { 0 };

is an assignment, not a declaration, so it won't work. You should loop.

int myArray[10000] = { 0 };

for(int i = 0; i < 1000; i++) {
    for (int j = 0; j < 10000; j++) {
        myArray[j] = ;  // put your value here.
    }
}

I am unsure of the purpose of this. Benchmarking?

edited May 8, 2016 at 15:27

answered May 8, 2016 at 15:22

totoro

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Comments

ddz · Accepted Answer · 2016-05-08 15:49:34Z

0

The trivial implementation of memset, without any optimization, is a loop that set each position of an array to a desired value. The problem is memset do this for each byte, and it is not what you want. I recommend you to implement an alternative to memset:

int *mymemset (int *s, int v, size_t n) {
    unsigned int *p = s;
    while(n--) {
        *p++ = (unsigned int)v;
    }

    return s;
}

And use it to initialize your array.

edited May 8, 2016 at 15:49

answered May 8, 2016 at 15:08

ddz

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8 Comments

Jon S Over a year ago

But my array is of global scope(mentioned in question), not an auto/ local scope. I am using array for many other data manipulation.

ddz Over a year ago

oh.. ok. So you have a global array that you want to initialize with 0s or whatever 1k times? Isn't this a design problem?

Jon S Over a year ago

Yes, but I have to strongly go with this option, because of data processing in multiple parts of the code.

Jon S Over a year ago

Thanks alot!!, But not able to upvote, because I have less than 15 reputation. Btw I have to call mymemset (myArray, 0, 10000); Is n't it?

ddz Over a year ago

Yes. Or mymemset(myArray, 5, 10000);. Try and see if this solves your problem. If it does, accept as an answer. Please note that *p++ = (unsigned int)v; won't be able to set negative values. Remove the cast if you want to use negative numbers.

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