How do I test if a string is empty in Objective-C

Question

How do I test if an NSString is empty in Objective-C

User · Answer

You should better use this category    implementation NSString  Empty       -  BOOL  isWhitespace          return    self stringByTrimmingCharactersInSet  NSCharacterSet whitespaceAndNewlineCharacterSet  length     0           end

User · Answer

Another option is to check if it is equal to     with isEqualToString  like so   if   myString isEqualToString             NSLog   myString IS empty       else       NSLog   myString IS NOT empty  it is       myString

User · Answer

So aside from the basic concept of checking for a string length less than 1  it is important to consider context deeply    Languages human or computer or otherwise might have different definitions of empty strings and within those same languages  additional context may further change the meaning    Let s say empty string means  a string which does not contain any characters significant in the current context     This could mean visually  as in color and background color are same in an attributed string  Effectively empty    This could mean empty of meaningful characters  All dots or all dashes or all underscores might be considered empty   Further  empty of meaningful significant characters could mean a string that has no characters the reader understands   They could be characters in a language or characterSet defined as meaningless to the reader  We could define it a little differently to say the string forms no known words in a given language    We could say empty is a function of the percentage of negative space in the glyphs rendered    Even a sequence of non printable characters with no general visual representation is not truly empty  Control characters come to mind  Especially the low ASCII range  I m surprised nobody mentioned those as they hose lots of systems and are not whitespace as they normally have no glyphs and no visual metrics   Yet the string length is not zero    Conclusion   Length alone is not the only measure here   Contextual set membership is also pretty important    Character Set membership is a very important common additional measure   Meaningful sequences are also a fairly common one    think SETI or crypto or captchas   Additional more abstract context sets also exist    So think carefully before assuming a string is only empty based on length or whitespace

User · Answer

Marc s answer is correct   But I ll take this opportunity to include a pointer to Wil Shipley s generalized isEmpty  which he shared on his blog   static inline BOOL IsEmpty id thing    return thing    nil      thing respondsToSelector  selector length    amp  amp    NSData   thing length     0       thing respondsToSelector  selector count    amp  amp    NSArray   thing count     0

User · Answer

Just pass your string to following method     BOOL isEmpty  NSString   str       if str length  0     str isKindOfClass  NSNull class       str isEqualToString        str  isEqualToString NULL    str isEqualToString    null     str  nil     str isEqualToString    lt null gt              return YES            return NO

User · Answer

-  BOOL isEmpty  NSString   string      if   NSNull    string     NSNull null             return YES            if  string    nil            return YES            if   string length     0            return YES            if    string stringByTrimmingCharactersInSet   NSCharacterSet whitespaceAndNewlineCharacterSet   length     0            return YES            if   string stringByStrippingWhitespace  isEqualToString                return YES            return NO

User · Answer

Swift Version Even though this is an Objective C question  I needed to use NSString in Swift so I will also include an answer here  let myNSString  NSString    quot  quot   if myNSString length    0       print  quot String is empty  quot      Or if NSString is an Optional  var myOptionalNSString  NSString    nil  if myOptionalNSString    nil    myOptionalNSString  length    0       print  quot String is empty  quot         or alternatively    if let myString   myOptionalNSString       if myString length    0           print  quot String is not empty  quot            The normal Swift String version is let myString  String    quot  quot   if myString isEmpty       print  quot String is empty  quot      See also  Check empty string in Swift

User · Answer

Simply Check your string length   if   yourString length          your code        a message to NIL will return nil or 0  so no need to test for nil      Happy coding

User · Answer

Try the following  NSString  stringToCheck         if   stringToCheck isEqualToString            NSLog   String Empty      else      NSLog   String Not Empty

User · Answer

You have 2 methods to check whether the string is empty or not   Let s suppose your string name is NSString  strIsEmpty   Method 1     if strIsEmpty length  0          String is empty    else         String is not empty     Method 2     if  strIsEmpty isEqualToString               String is empty    else         String is not empty     Choose any of the above method and get to know whether string is empty or not

User · Answer

Its as simple as if  myString isEqual       or if  myString isEqualToString

User · Answer

The best way in any case is to check the length of the given string For this if your string is myString then the code is       int len    myString length       if len    0          NSLog   String is empty              else        NSLog   String is        myString

User · Answer

It is working as charm for me  If the NSString is s  if   s isKindOfClass  NSNull class      s    nil     s isEqualToString              NSLog   s is empty       else        NSLog   s containing      s

User · Answer

if str length    0     str isKindOfClass   NSNull class         NSLog   String is empty      else      NSLog   String is not empty

User · Answer

I have checked an empty string using below code      Check if we have any search terms in the search dictionary  if   strMyString text   id   NSNull null      strMyString text length   0            strMyString text isEqual              AlertView showAlert   Please enter a valid string

User · Answer

You can check either your string is empty or not my using this method     BOOL  isEmptyString    NSString   string       if  string length     0     string isKindOfClass  NSNull class               string isEqualToString        string  isEqualToString NULL             string    nil                 return YES            IF String Is An Empty String            return NO      Best practice is to make a shared class say UtilityClass and ad this method so that you would be able to use this method by just calling it through out your application

User · Answer

One of the best solution I ever seen  better than Matt G s one  is this improved inline function I picked up on some Git Hub repo  Wil Shipley s one  but I can t find the link         Check if the  thing  passed is empty static inline BOOL isEmpty id thing        return thing    nil         thing isKindOfClass  NSNull class            thing respondsToSelector  selector length            amp  amp    NSData   thing length     0           thing respondsToSelector  selector count            amp  amp    NSArray   thing count     0

User · Answer

The first approach is valid  but doesn t work if your string has blank spaces                  So you must clear this white spaces before testing it   This code clear all the blank spaces on both sides of the string    stringObject stringByTrimmingCharactersInSet  NSCharacterSet whitespaceCharacterSet       One good idea is create one macro  so you don t have to type this monster line    define allTrim  object    object stringByTrimmingCharactersInSet  NSCharacterSet whitespaceCharacterSet      Now you can use   NSString  emptyString            if    allTrim  emptyString   length     0   NSLog   Is empty

User · Answer

if  string length    0  stringIsEmpty

User · Answer

You can have an empty string in two ways   1               Does not contain space   2               Contain Space  Technically both the strings are empty  We can write both the things just by using ONE Condition  if   firstNameTF text stringByReplacingOccurrencesOfString      withString      length  0        NSLog   Empty String      else       NSLog   String contains some value

User · Answer

check this     if   yourString isEqualToString             NsLog   Blank String        Or  if   yourString length     0        NsLog   Blank String        Hope this will help

User · Answer

You can easily check if string is empty with this     if   yourstring isEqualToString                execute your action here if string is empty

User · Answer

if   txtMobile text length     0          Utility showAlertWithTitleAndMessage  AMLocalizedString   Invalid Mobile No  nil  message  AMLocalizedString   Enter valid Mobile Number  nil

User · Answer

I put this    implementation NSObject  AdditionalMethod  - BOOL  isNotEmpty       return   self    nil         self isKindOfClass  NSNull class            self respondsToSelector  selector length            amp  amp    NSData   self length     0           self respondsToSelector  selector count            amp  amp    NSArray   self count     0         end   The problem is that if self is nil  this function is never called  It ll return false  which is desired

User · Answer

You can check if  string length     0  This will check if it s a valid but empty string       as well as if it s nil  since calling length on nil will also return 0

User · Answer

The best way is to use the category  You can check the following function  Which has all the conditions to check   - BOOL isNullString  NSString   aStr          if   NSNull   aStr isKindOfClass  NSNull class                 return YES                    if   NSNull   aStr      NSNull null                 return YES                    if   aStr isKindOfClass  NSNull class                 return YES                    if    aStr stringByTrimmingCharactersInSet  NSCharacterSet whitespaceAndNewlineCharacterSet   length                return YES                    return NO

User · Answer

Just use one of the if else conditions as shown below   Method 1   if   yourString isEqualToString                    yourString is empty        else              yourString has some text on it          Method 2   if   yourString length     0           Empty yourString   else          yourString is not empty

User · Answer

Very useful post  to add NSDictionary support as well one small change   static inline BOOL isEmpty id thing        return thing    nil         thing isKindOfClass  NSNull class            thing respondsToSelector  selector length            amp  amp    thing respondsToSelector  selector count            amp  amp    NSData   thing length     0           thing respondsToSelector  selector count            amp  amp   thing count     0

User · Answer

Different validations   NSString   inputStr     Hey       Check length  inputStr length     Coming from server  check if its NSNull  inputStr isEqual  NSNull null     nil   inputStr    For validation in allowed character set - BOOL validateString  NSString  inputStr       BOOL isValid   NO      if    inputStr length  gt 0                 return isValid              NSMutableCharacterSet  allowedSet    NSMutableCharacterSet characterSetWithCharactersInString    -         allowedSet formUnionWithCharacterSet  NSCharacterSet decimalDigitCharacterSet        if   inputStr rangeOfCharacterFromSet  allowedSet invertedSet   location    NSNotFound                   contains only decimal set and  -  and                else                  invalid         isValid   NO             return isValid

User · Answer

May be this answer is the duplicate of already given answers  but i did few modification and changes in the order of checking the conditions  Please refer the below code         BOOL isStringEmpty  NSString   str               if str    nil     str isKindOfClass  NSNull class      str length  0                return YES                   return NO

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