initializing strings as null vs empty string

Question

How would it matter if my C   code  as shown below  has a string initialized as an empty string    std  string myStr           some code to optionally populate  myStr     if  myStr                 do something     vs  no null initialization   std  string myStr      some code to optionally populate  myStr     if  myStr    NULL           do something     Are there any best practices or gotchas around this

User · Answer

The default constructor initializes the string to the empty string. This is the more economic way of saying the same thing.

However, the comparison to NULL stinks. That is an older syntax still in common use that means something else; a null pointer. It means that there is no string around.

If you want to check whether a string (that does exist) is empty, use the empty method instead:

if (myStr.empty()) ...

User · Answer

Best    std  string subCondition    This creates an empty string   This   std  string myStr         does a copy initialization - creates a temporary string from     and then uses the copy constructor to create myStr   Bonus   std  string myStr        does a direct initialization and uses the string const char   constructor   To check if a string is empty  just use empty

User · Answer

Empty-ness and  NULL-ness  are two different concepts  As others mentioned the former can be achieved via std  string  empty    the latter can be achieved with boost  optional lt std  string gt   e g    boost  optional lt string gt  myStr  if  myStr       myStr    NULL

User · Answer

I would prefere   if   myStr empty            do something     Also you don t have to write std  string a        You can just write std  string a  - it will be empty by default

User · Answer

There are no gotchas  The default construction of std  string is     But you cannot compare a string to NULL  The closest you can get is to check whether the string is empty or not  using the std  string  empty method

User · Answer

There s a function empty   ready for you in std  string   std  string a  if a empty            do stuff  You will enter this block if the string is declared like this     or  std  string a  if  a empty            You will not enter this block now   a    42   if  a empty            And now you will enter this block

[c++] initializing strings as null vs. empty string

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