[c] Best way to check if a character array is empty

Which is the most reliable way to check if a character array is empty?

char text[50];

if(strlen(text) == 0) {}

or

if(text[0] == '\0') {}

or do i need to do

 memset(text, 0, sizeof(text));
 if(strlen(text) == 0) {}

Whats the most efficient way to go about this?

The second one is fastest. Using strlen will be close if the string is indeed empty, but strlen will always iterate through every character of the string, so if it is not empty, it will do much more work than you need it to.

As James mentioned, the third option wipes the string out before checking, so the check will always succeed but it will be meaningless.

This will work to find if a character array is empty. It probably is also the fastest.

if(text[0] == '\0') {}

This will also be fast if the text array is empty. If it contains characters it needs to count all the characters in it first.

if(strlen(text) == 0) {}

if (!*text) {}  

The above dereferences the pointer 'text' and checks to see if it's zero. alternatively:

if (*text == 0) {} 

Depends on whether or not your array is holding a null-terminated string. If so, then

if(text[0] == '\0') {}

should be sufficient.

Edit: Another method would be...

if (strcmp(text, "") == 0)

which is potentially less efficient but clearly expresses your intent.

if (text[0] == '\0')
{
    /* Code... */
}

Use this if you're coding for micro-controllers with little space on flash and/or RAM. You will waste a lot more flash using strlen than checking the first byte.

The above example is the fastest and less computation is required.

The second method would almost certainly be the fastest way to test whether a null-terminated string is empty, since it involves one read and one comparison. There's certainly nothing wrong with this approach in this case, so you may as well use it.

The third method doesn't check whether a character array is empty; it ensures that a character array is empty.