How to empty a char array?

Question

Have an array of chars like char members[255]. How can I empty it completely without using a loop?

char members[255];

By "empty" I mean that if it had some values stored in it then it should not. For example if I do strcat then old value should not remain

members = "old value";

//empty it efficiently
strcat(members,"new"); // should return only new and not "old value new"

Answer 1

I'd go with

members_in_use = 0;

Answer 2

char members[255] = {0};

Answer 3

using

  memset(members, 0, 255);

in general

  memset(members, 0, sizeof members);

if the array is in scope, or

  memset(members, 0, nMembers * (sizeof members[0]) );

if you only have the pointer value, and nMembers is the number of elements in the array.

---

EDIT Of course, now the requirement has changed from the generic task of clearing an array to purely resetting a string, memset is overkill and just zeroing the first element suffices (as noted in other answers).

Answer 4

Depends on what you mean by 'empty':

members[0] = '\0';

Answer 5

By "empty an array" if you mean reset to 0, then you can use bzero.

#include <strings.h>  
void bzero(void *s, size_t n);

If you want to fill the array with some other default character then you may use memset function.

#include <string.h>  
void *memset(void *s, int c, size_t n);

Answer 6

You cannot empty an array as such, it always contains the same amount of data.

In a bigger context the data in the array may represent an empty list of items, but that has to be defined in addition to the array. The most common ways to do this is to keep a count of valid items (see the answer by pmg) or for strings to terminate them with a zero character (the answer by Felix). There are also more complicated ways, for example a ring buffer uses two indices for the positions where data is added and removed.

Answer 7

members[0] = 0;

is enough, given your requirements.

Notice however this is not "emptying" the buffer. The memory is still allocated, valid character values may still exist in it, and so forth..

Answer 8

Disclaimer: I don't usually program in C so there may be any syntax gotcha in my examples, but I hope the ideas I try to express are clear.

If "emptying" means "containing an empty string", you can just assign the first array item to zero, which will effectively make the array to contain an empry string:

members[0] = 0;

If "emptying" means "freeing the memory it is using", you should not use a fixed char array in the first place. Rather, you should define a pointer to char, and then do malloc / free (or string assignment) as appropriate.

An example using only static strings:

char* emptyString="";
char* members;

//Set string value
members = "old value";

//Empty string value
member = emptyString

//Will return just "new"
strcat(members,"new");

Answer 9

simpler is better - make sense?

in this case just members[0] = 0 works. don't make a simple question so complicated.

Answer 10

Given the bickering that is going on for such a basic operation, I thought I'd post something less silly than that.

The solution is simple, try this:

/* Dear Compiler:
 * Please magically set the first byte to NULL when I need it
 * to be :) Thank you!
 */

Answer 11

Don't bother trying to zero-out your char array if you are dealing with strings. Below is a simple way to work with the char strings.

Copy (assign new string):

strcpy(members, "blond girls");

Concatenate (add the string):

strcat(members, " are stupid!");

Empty string:

members[0] = 0;

Simple like that.