Best way to check if a character array is empty

Question

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

User · Answer

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) {}

User · Answer

if    text         The above dereferences the pointer  text  and checks to see if it s zero   alternatively   if   text    0

User · Answer

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

User · Answer

Given this code   char text 50   if strlen text     0       Followed by a question about this code    memset text  0  sizeof text     if strlen text     0       I smell confusion   Specifically  in this case   char text 50   if strlen text     0           the contents of text   will be uninitialized and undefined   Thus  strlen text  will return an undefined result   The easiest fastest way to ensure that a C string is initialized to the empty string is to simply set the first byte to 0   char text 50   text 0    0    From then  both strlen text  and the very-fast-but-not-as-straightforward  text 0     0  tests will both detect the empty string

User · Answer

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

User · Answer

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

User · Answer

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

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

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