Do you use NULL or 0 zero for pointers in C

Question

In the early days of C   when it was bolted on top of C  you could not use NULL as it was defined as  void  0  You could not assign NULL to any pointer other than void   which made it kind of useless  Back in those days  it was accepted that you used 0  zero  for null pointers   To this day  I have continued to use zero as a null pointer but those around me insist on using NULL  I personally do not see any benefit to giving a name  NULL  to an existing value - and since I also like to test pointers as truth values   if  p  amp  amp   q    do something      then using zero makes more sense  as in if you use NULL  you cannot logically use p  amp  amp   q - you need to explicitly compare against NULL  unless you assume NULL is zero  in which case why use NULL    Is there any objective reason to prefer zero over NULL  or vice versa   or is all just personal preference   Edit  I should add  and meant to originally say  that with RAII and exceptions  I rarely use zero NULL pointers  but sometimes you do need them still

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I always use    NULL for pointers   0  for chars 0 0 for floats and doubles   where 0 would do fine  It is a matter of signaling intent  That said  I am not anal about it

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Use NULL   NULL shows your intent   That it is 0 is an implementation detail that should not matter

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Mostly personal preference  though one could make the argument that NULL makes it quite obvious that the object is a pointer which currently doesn t point to anything  e g   void  ptr    amp something     lots o  code    ptr   NULL     more obvious that it s a pointer and not being used   IIRC  the standard does not require NULL to be 0  so using whatever is defined in  lt stddef h gt  is probably best for your compiler   Another facet to the argument is whether you should use logical comparisons  implicit cast to bool  or explicity check against NULL  but that comes down to readability as well

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I think the standard guarantees that NULL    0  so you can do either   I prefer NULL because it documents your intent

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I always use    NULL for pointers   0  for chars 0 0 for floats and doubles   where 0 would do fine  It is a matter of signaling intent  That said  I am not anal about it

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Here s Stroustrup s take on this  C   Style and Technique FAQ  In C    the definition of NULL is 0  so there is only an aesthetic difference  I prefer to avoid macros  so I use 0  Another problem with NULL is that people sometimes mistakenly believe that it is different from 0 and or not an integer  In pre-standard code  NULL was is sometimes defined to something unsuitable and therefore had has to be avoided  That s less common these days  If you have to name the null pointer  call it nullptr  that s what it s called in C  11  Then  nullptr will be a keyword   That said  don t sweat the small stuff

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If I recall correctly NULL is defined differently in the headers that I have used  For C it is defined as  void  0  and for C   it s defines as just 0  The code looked something like    ifndef   cplusplus  define NULL  void  0  else  define NULL 0  endif   Personally I still use the NULL value to represent null pointers  it makes it explicit that you re using a pointer rather than some integral type  Yes internally the NULL value is still 0 but it isn t represented as such    Additionally I don t rely on the automatic conversion of integers to boolean values but explicitly compare them   For example prefer to use   if  pointer value    NULL    integer value    0    rather than   if  pointer value     integer value      Suffice to say that this is all remedied in C  11 where one can simply use nullptr instead of NULL  and also nullptr t that is the type of a nullptr

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I prefer to use NULL as it makes clear that your intent is the value represents a pointer not an arithmetic value   The fact that it s a macro is unfortunate  but since it s so widely ingrained there s little danger  unless someone does something really boneheaded    I do wish it were a keyword from the beginning  but what can you do   That said  I have no problem with using pointers as truth values in themselves   Just as with NULL  it s an ingrained idiom   C  09 will add the the nullptr construct which I think is long overdue

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I try to avoid the whole question by using C   references where possible   Rather than  void foo const Bar  pBar            you might often be able to write  void foo const Bar amp  bar            Of course  this doesn t always work  but null pointers can be overused

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I prefer to use NULL as it makes clear that your intent is the value represents a pointer not an arithmetic value   The fact that it s a macro is unfortunate  but since it s so widely ingrained there s little danger  unless someone does something really boneheaded    I do wish it were a keyword from the beginning  but what can you do   That said  I have no problem with using pointers as truth values in themselves   Just as with NULL  it s an ingrained idiom   C  09 will add the the nullptr construct which I think is long overdue

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Here s Stroustrup s take on this  C   Style and Technique FAQ  In C    the definition of NULL is 0  so there is only an aesthetic difference  I prefer to avoid macros  so I use 0  Another problem with NULL is that people sometimes mistakenly believe that it is different from 0 and or not an integer  In pre-standard code  NULL was is sometimes defined to something unsuitable and therefore had has to be avoided  That s less common these days  If you have to name the null pointer  call it nullptr  that s what it s called in C  11  Then  nullptr will be a keyword   That said  don t sweat the small stuff

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Strange  nobody  including Stroustroup mentioned that  While talking a lot about standards and aesthetics nobody noticed that it is dangerous to use 0 in NULL s stead  for instance  in variable argument list on the architecture where sizeof int     sizeof void    Like Stroustroup  I prefer 0 for aesthetic reasons  but one has to be careful not to use it where its type might be ambiguous

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I prefer to use NULL as it makes clear that your intent is the value represents a pointer not an arithmetic value   The fact that it s a macro is unfortunate  but since it s so widely ingrained there s little danger  unless someone does something really boneheaded    I do wish it were a keyword from the beginning  but what can you do   That said  I have no problem with using pointers as truth values in themselves   Just as with NULL  it s an ingrained idiom   C  09 will add the the nullptr construct which I think is long overdue

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I once worked on a machine where 0 was a valid address and NULL was defined as a special octal value   On that machine  0    NULL   so code such as  char  p        if  p            would not work as you expect   You HAD to write   if  p    NULL            Although I believe most compilers define NULL as 0 these days I still remember the lesson from those years ago   NULL is not necessarily 0

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There are a few arguments  one of which is relatively recent  which I believe contradict Bjarne s position on this   Documentation of intent Using NULL allows for searches on its use and it also highlights that the developer wanted to use a NULL pointer  irrespective of whether it is being interpreted by the compiler as NULL or not   Overload of pointer and  int  is relatively rare The example that everybody quotes is   void foo int     void foo  int     void bar        foo  NULL       Calls  foo int       However  at least in my opinion  the problem with the above is not that we re using NULL for the null pointer constant  it s that we have overloads of foo   which take very different kinds of arguments   The parameter must be an int too  as any other type will result in an ambiguous call and so generate a helpful compiler warning   Analysis tools can help TODAY  Even in the absence of C  0x  there are tools available today that verify that NULL is being used for pointers  and that 0 is being used for integral types   C   11 will have a new std  nullptr t type  This is the newest argument to the table   The problem of 0 and NULL is being actively addressed for C  0x  and you can guarantee that for every implementation that provides NULL  the very first thing that they will do is    define NULL  nullptr  For those who use NULL rather than 0  the change will be an improvement in type-safety with little or no effort - if anything it may also catch a few bugs where they ve used NULL for 0   For anybody using 0 today    well  hopefully they have a good knowledge of regular expressions

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Here s Stroustrup s take on this  C   Style and Technique FAQ  In C    the definition of NULL is 0  so there is only an aesthetic difference  I prefer to avoid macros  so I use 0  Another problem with NULL is that people sometimes mistakenly believe that it is different from 0 and or not an integer  In pre-standard code  NULL was is sometimes defined to something unsuitable and therefore had has to be avoided  That s less common these days  If you have to name the null pointer  call it nullptr  that s what it s called in C  11  Then  nullptr will be a keyword   That said  don t sweat the small stuff

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Here s Stroustrup s take on this  C   Style and Technique FAQ  In C    the definition of NULL is 0  so there is only an aesthetic difference  I prefer to avoid macros  so I use 0  Another problem with NULL is that people sometimes mistakenly believe that it is different from 0 and or not an integer  In pre-standard code  NULL was is sometimes defined to something unsuitable and therefore had has to be avoided  That s less common these days  If you have to name the null pointer  call it nullptr  that s what it s called in C  11  Then  nullptr will be a keyword   That said  don t sweat the small stuff

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I m with Stroustrup on this one  -  Since NULL is not part of the language  I prefer to use 0

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I m with Stroustrup on this one  -  Since NULL is not part of the language  I prefer to use 0

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cerr  lt  lt  sizeof 0   lt  lt  endl      cerr  lt  lt  sizeof NULL   lt  lt  endl      cerr  lt  lt  sizeof void    lt  lt  endl                        On a 64-bit gcc RHEL platform you get      4     8     8                        The moral of the story   You should use NULL when you re dealing with pointers   1  It declares your intent  don t make me search through all your code trying to figure out if a variable is a pointer or some numeric type    2  In certain API calls that expect variable arguments  they ll use a NULL-pointer to indicate the end of the argument list   In this case  using a  0  instead of NULL can cause problems   On a 64-bit platform  the va arg call wants a 64-bit pointer  yet you ll be passing only a 32-bit integer   Seems to me like you re relying on the other 32-bits to be zeroed out for you   I ve seen certain compilers  e g  Intel s icpc  that aren t so gracious -- and this has resulted in runtime errors

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There are a few arguments  one of which is relatively recent  which I believe contradict Bjarne s position on this   Documentation of intent Using NULL allows for searches on its use and it also highlights that the developer wanted to use a NULL pointer  irrespective of whether it is being interpreted by the compiler as NULL or not   Overload of pointer and  int  is relatively rare The example that everybody quotes is   void foo int     void foo  int     void bar        foo  NULL       Calls  foo int       However  at least in my opinion  the problem with the above is not that we re using NULL for the null pointer constant  it s that we have overloads of foo   which take very different kinds of arguments   The parameter must be an int too  as any other type will result in an ambiguous call and so generate a helpful compiler warning   Analysis tools can help TODAY  Even in the absence of C  0x  there are tools available today that verify that NULL is being used for pointers  and that 0 is being used for integral types   C   11 will have a new std  nullptr t type  This is the newest argument to the table   The problem of 0 and NULL is being actively addressed for C  0x  and you can guarantee that for every implementation that provides NULL  the very first thing that they will do is    define NULL  nullptr  For those who use NULL rather than 0  the change will be an improvement in type-safety with little or no effort - if anything it may also catch a few bugs where they ve used NULL for 0   For anybody using 0 today    well  hopefully they have a good knowledge of regular expressions

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I always use    NULL for pointers   0  for chars 0 0 for floats and doubles   where 0 would do fine  It is a matter of signaling intent  That said  I am not anal about it

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I always use 0  Not for any real thought out reason  just because when I was first learning C   I read something that recommended using 0 and I ve just always done it that way  In theory there could be a confusion issue in readability but in practice I have never once come across such an issue in thousands of man-hours and millions of lines of code  As Stroustrup says  it s really just a personal aesthetic issue until the standard becomes nullptr

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cerr  lt  lt  sizeof 0   lt  lt  endl      cerr  lt  lt  sizeof NULL   lt  lt  endl      cerr  lt  lt  sizeof void    lt  lt  endl                        On a 64-bit gcc RHEL platform you get      4     8     8                        The moral of the story   You should use NULL when you re dealing with pointers   1  It declares your intent  don t make me search through all your code trying to figure out if a variable is a pointer or some numeric type    2  In certain API calls that expect variable arguments  they ll use a NULL-pointer to indicate the end of the argument list   In this case  using a  0  instead of NULL can cause problems   On a 64-bit platform  the va arg call wants a 64-bit pointer  yet you ll be passing only a 32-bit integer   Seems to me like you re relying on the other 32-bits to be zeroed out for you   I ve seen certain compilers  e g  Intel s icpc  that aren t so gracious -- and this has resulted in runtime errors

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Use NULL   NULL shows your intent   That it is 0 is an implementation detail that should not matter

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Mostly personal preference  though one could make the argument that NULL makes it quite obvious that the object is a pointer which currently doesn t point to anything  e g   void  ptr    amp something     lots o  code    ptr   NULL     more obvious that it s a pointer and not being used   IIRC  the standard does not require NULL to be 0  so using whatever is defined in  lt stddef h gt  is probably best for your compiler   Another facet to the argument is whether you should use logical comparisons  implicit cast to bool  or explicity check against NULL  but that comes down to readability as well

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Someone told me once    I am going to redefine NULL to 69  Since then I don t use it  P  It makes your code quite vulnerable   Edit   Not everything in the standard is perfect  The macro NULL is an implementation-defined C   null pointer constant not fully compatible with C NULL macro  what besides the type hiding implicit convert it in a useless and prone to errors tool    NULL does not behaves as a null pointer but as a O OL literal    Tell me next example is not confusing    void foo char      void foo int    foo NULL      calls int version instead of pointer version     Is because of all that  in the new standard appears std  nullptr t  If you don t want to wait for the new standard and want to use a nullptr  use at least a decent one like the proposed by Meyers  see jon h comment

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I stopped using NULL in favor of 0 long ago  as well as as most other macros   I did this not only because I wanted to avoid macros as much as possible  but also because NULL seems to have become over-used in C and C   code  It seems to be used whenever a 0 value is needed  not just for pointers   On new projects  I put this in a project header   static const int nullptr   0    Now  when C  0x compliant compilers arrive  all I have to do is remove that line  A nice benefit of this is that Visual Studio already recognizes nullptr as a keyword and highlights it appropriately

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I would say history has spoken and those who argued in favour of using 0  zero  were wrong  including Bjarne Stroustrup   The arguments in favour of 0 were mostly aesthetics and  personal preference    After the creation of C  11  with its new nullptr type  some compilers have started complaining  with default parameters  about passing 0 to functions with pointer arguments  because 0 is not a pointer    If the code had been written using NULL  a simple search and replace could have been performed through the codebase to make it nullptr instead  If you are stuck with code written using the choice of 0 as a pointer it is far more tedious to update it   And if you have to write new code right now to the C  03 standard  and can t use nullptr   you really should just use NULL  It ll make it much easier for you to update in the future

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Setting a pointer to 0 is just not that clear   Especially if you come a language other than C     This includes C as well as Javascript   I recently delt with some code like so   virtual void DrawTo BITMAP  buffer   0   for pure virtual function for the first time   I thought it to be some magic jiberjash for a week   When I realized it was just basically setting the function pointer to a null  as virtual functions are just function pointers in most cases for C    I kicked myself   virtual void DrawTo BITMAP  buffer   null   would have been less confusing than that basterdation without proper spacing to my new eyes   Actually  I am wondering why C   doesn t employ lowercase null much like it employes lowercase false and true now

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I think the standard guarantees that NULL    0  so you can do either   I prefer NULL because it documents your intent

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There are a few arguments  one of which is relatively recent  which I believe contradict Bjarne s position on this   Documentation of intent Using NULL allows for searches on its use and it also highlights that the developer wanted to use a NULL pointer  irrespective of whether it is being interpreted by the compiler as NULL or not   Overload of pointer and  int  is relatively rare The example that everybody quotes is   void foo int     void foo  int     void bar        foo  NULL       Calls  foo int       However  at least in my opinion  the problem with the above is not that we re using NULL for the null pointer constant  it s that we have overloads of foo   which take very different kinds of arguments   The parameter must be an int too  as any other type will result in an ambiguous call and so generate a helpful compiler warning   Analysis tools can help TODAY  Even in the absence of C  0x  there are tools available today that verify that NULL is being used for pointers  and that 0 is being used for integral types   C   11 will have a new std  nullptr t type  This is the newest argument to the table   The problem of 0 and NULL is being actively addressed for C  0x  and you can guarantee that for every implementation that provides NULL  the very first thing that they will do is    define NULL  nullptr  For those who use NULL rather than 0  the change will be an improvement in type-safety with little or no effort - if anything it may also catch a few bugs where they ve used NULL for 0   For anybody using 0 today    well  hopefully they have a good knowledge of regular expressions

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I always use 0  Not for any real thought out reason  just because when I was first learning C   I read something that recommended using 0 and I ve just always done it that way  In theory there could be a confusion issue in readability but in practice I have never once come across such an issue in thousands of man-hours and millions of lines of code  As Stroustrup says  it s really just a personal aesthetic issue until the standard becomes nullptr

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I always use 0  Not for any real thought out reason  just because when I was first learning C   I read something that recommended using 0 and I ve just always done it that way  In theory there could be a confusion issue in readability but in practice I have never once come across such an issue in thousands of man-hours and millions of lines of code  As Stroustrup says  it s really just a personal aesthetic issue until the standard becomes nullptr

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Using either 0 or NULL will have the same effect   However  that doesn t mean that they are both good programming practices  Given that there is no difference in performance  choosing a low-level-aware option over an agnostic abstract alternative is a bad programming practice  Help readers of your code understand your thought process    NULL  0  0 0    0   0x00 and whatelse all translate to the same thing  but are different logical entities in your program  They should be used as such  NULL is a pointer  0 is quantity  0x0 is a value whose bits are interesting etc  You wouldn t assign   0  to a pointer whether it compiles or not   I know some communities encourage demonstrating in-depth knowledge of an environment by breaking the environment s contracts  Responsible programmers  however  make maintainable code and keep such practices out of their code

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If I recall correctly NULL is defined differently in the headers that I have used  For C it is defined as  void  0  and for C   it s defines as just 0  The code looked something like    ifndef   cplusplus  define NULL  void  0  else  define NULL 0  endif   Personally I still use the NULL value to represent null pointers  it makes it explicit that you re using a pointer rather than some integral type  Yes internally the NULL value is still 0 but it isn t represented as such    Additionally I don t rely on the automatic conversion of integers to boolean values but explicitly compare them   For example prefer to use   if  pointer value    NULL    integer value    0    rather than   if  pointer value     integer value      Suffice to say that this is all remedied in C  11 where one can simply use nullptr instead of NULL  and also nullptr t that is the type of a nullptr

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I usually use 0  I don t like macros  and there s no guarantee that some third party header you re using doesn t redefine NULL to be something odd   You could use a nullptr object as proposed by Scott Meyers and others until C   gets a nullptr keyword   const    It is a const object    class nullptr t    public      template lt class T gt      operator T    const    convertible to any type of null non-member pointer          return 0         template lt class C  class T gt      operator T C      const      or any type of null member pointer          return 0     private      void operator amp    const      Can t take address of nullptr    nullptr         Google  nullptr  for more info

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Well I argue for not using 0 or NULL pointers at all whenever possible   Using them will sooner or later lead to segmentation faults in your code  In my experience this  and pointers in gereral is one of the biggest source of bugs in C    also  it leads to  if-not-null  statements all over your code  Much nicer if you can rely on always a valid state   There is almost always a better alternative

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Mostly personal preference  though one could make the argument that NULL makes it quite obvious that the object is a pointer which currently doesn t point to anything  e g   void  ptr    amp something     lots o  code    ptr   NULL     more obvious that it s a pointer and not being used   IIRC  the standard does not require NULL to be 0  so using whatever is defined in  lt stddef h gt  is probably best for your compiler   Another facet to the argument is whether you should use logical comparisons  implicit cast to bool  or explicity check against NULL  but that comes down to readability as well

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Use NULL   NULL shows your intent   That it is 0 is an implementation detail that should not matter

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I once worked on a machine where 0 was a valid address and NULL was defined as a special octal value   On that machine  0    NULL   so code such as  char  p        if  p            would not work as you expect   You HAD to write   if  p    NULL            Although I believe most compilers define NULL as 0 these days I still remember the lesson from those years ago   NULL is not necessarily 0

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I stopped using NULL in favor of 0 long ago  as well as as most other macros   I did this not only because I wanted to avoid macros as much as possible  but also because NULL seems to have become over-used in C and C   code  It seems to be used whenever a 0 value is needed  not just for pointers   On new projects  I put this in a project header   static const int nullptr   0    Now  when C  0x compliant compilers arrive  all I have to do is remove that line  A nice benefit of this is that Visual Studio already recognizes nullptr as a keyword and highlights it appropriately

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Someone told me once    I am going to redefine NULL to 69  Since then I don t use it  P  It makes your code quite vulnerable   Edit   Not everything in the standard is perfect  The macro NULL is an implementation-defined C   null pointer constant not fully compatible with C NULL macro  what besides the type hiding implicit convert it in a useless and prone to errors tool    NULL does not behaves as a null pointer but as a O OL literal    Tell me next example is not confusing    void foo char      void foo int    foo NULL      calls int version instead of pointer version     Is because of all that  in the new standard appears std  nullptr t  If you don t want to wait for the new standard and want to use a nullptr  use at least a decent one like the proposed by Meyers  see jon h comment

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I always use 0  Not for any real thought out reason  just because when I was first learning C   I read something that recommended using 0 and I ve just always done it that way  In theory there could be a confusion issue in readability but in practice I have never once come across such an issue in thousands of man-hours and millions of lines of code  As Stroustrup says  it s really just a personal aesthetic issue until the standard becomes nullptr

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Mostly personal preference  though one could make the argument that NULL makes it quite obvious that the object is a pointer which currently doesn t point to anything  e g   void  ptr    amp something     lots o  code    ptr   NULL     more obvious that it s a pointer and not being used   IIRC  the standard does not require NULL to be 0  so using whatever is defined in  lt stddef h gt  is probably best for your compiler   Another facet to the argument is whether you should use logical comparisons  implicit cast to bool  or explicity check against NULL  but that comes down to readability as well

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Strange  nobody  including Stroustroup mentioned that  While talking a lot about standards and aesthetics nobody noticed that it is dangerous to use 0 in NULL s stead  for instance  in variable argument list on the architecture where sizeof int     sizeof void    Like Stroustroup  I prefer 0 for aesthetic reasons  but one has to be careful not to use it where its type might be ambiguous

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There are a few arguments  one of which is relatively recent  which I believe contradict Bjarne s position on this   Documentation of intent Using NULL allows for searches on its use and it also highlights that the developer wanted to use a NULL pointer  irrespective of whether it is being interpreted by the compiler as NULL or not   Overload of pointer and  int  is relatively rare The example that everybody quotes is   void foo int     void foo  int     void bar        foo  NULL       Calls  foo int       However  at least in my opinion  the problem with the above is not that we re using NULL for the null pointer constant  it s that we have overloads of foo   which take very different kinds of arguments   The parameter must be an int too  as any other type will result in an ambiguous call and so generate a helpful compiler warning   Analysis tools can help TODAY  Even in the absence of C  0x  there are tools available today that verify that NULL is being used for pointers  and that 0 is being used for integral types   C   11 will have a new std  nullptr t type  This is the newest argument to the table   The problem of 0 and NULL is being actively addressed for C  0x  and you can guarantee that for every implementation that provides NULL  the very first thing that they will do is    define NULL  nullptr  For those who use NULL rather than 0  the change will be an improvement in type-safety with little or no effort - if anything it may also catch a few bugs where they ve used NULL for 0   For anybody using 0 today    well  hopefully they have a good knowledge of regular expressions

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Use NULL   NULL shows your intent   That it is 0 is an implementation detail that should not matter

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I always use    NULL for pointers   0  for chars 0 0 for floats and doubles   where 0 would do fine  It is a matter of signaling intent  That said  I am not anal about it

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Using either 0 or NULL will have the same effect   However  that doesn t mean that they are both good programming practices  Given that there is no difference in performance  choosing a low-level-aware option over an agnostic abstract alternative is a bad programming practice  Help readers of your code understand your thought process    NULL  0  0 0    0   0x00 and whatelse all translate to the same thing  but are different logical entities in your program  They should be used as such  NULL is a pointer  0 is quantity  0x0 is a value whose bits are interesting etc  You wouldn t assign   0  to a pointer whether it compiles or not   I know some communities encourage demonstrating in-depth knowledge of an environment by breaking the environment s contracts  Responsible programmers  however  make maintainable code and keep such practices out of their code

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Well I argue for not using 0 or NULL pointers at all whenever possible   Using them will sooner or later lead to segmentation faults in your code  In my experience this  and pointers in gereral is one of the biggest source of bugs in C    also  it leads to  if-not-null  statements all over your code  Much nicer if you can rely on always a valid state   There is almost always a better alternative

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I would say history has spoken and those who argued in favour of using 0  zero  were wrong  including Bjarne Stroustrup   The arguments in favour of 0 were mostly aesthetics and  personal preference    After the creation of C  11  with its new nullptr type  some compilers have started complaining  with default parameters  about passing 0 to functions with pointer arguments  because 0 is not a pointer    If the code had been written using NULL  a simple search and replace could have been performed through the codebase to make it nullptr instead  If you are stuck with code written using the choice of 0 as a pointer it is far more tedious to update it   And if you have to write new code right now to the C  03 standard  and can t use nullptr   you really should just use NULL  It ll make it much easier for you to update in the future

User · Answer

I stopped using NULL in favor of 0 long ago  as well as as most other macros   I did this not only because I wanted to avoid macros as much as possible  but also because NULL seems to have become over-used in C and C   code  It seems to be used whenever a 0 value is needed  not just for pointers   On new projects  I put this in a project header   static const int nullptr   0    Now  when C  0x compliant compilers arrive  all I have to do is remove that line  A nice benefit of this is that Visual Studio already recognizes nullptr as a keyword and highlights it appropriately

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I try to avoid the whole question by using C   references where possible   Rather than  void foo const Bar  pBar            you might often be able to write  void foo const Bar amp  bar            Of course  this doesn t always work  but null pointers can be overused

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I prefer to use NULL as it makes clear that your intent is the value represents a pointer not an arithmetic value   The fact that it s a macro is unfortunate  but since it s so widely ingrained there s little danger  unless someone does something really boneheaded    I do wish it were a keyword from the beginning  but what can you do   That said  I have no problem with using pointers as truth values in themselves   Just as with NULL  it s an ingrained idiom   C  09 will add the the nullptr construct which I think is long overdue

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I m with Stroustrup on this one  -  Since NULL is not part of the language  I prefer to use 0

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Setting a pointer to 0 is just not that clear   Especially if you come a language other than C     This includes C as well as Javascript   I recently delt with some code like so   virtual void DrawTo BITMAP  buffer   0   for pure virtual function for the first time   I thought it to be some magic jiberjash for a week   When I realized it was just basically setting the function pointer to a null  as virtual functions are just function pointers in most cases for C    I kicked myself   virtual void DrawTo BITMAP  buffer   null   would have been less confusing than that basterdation without proper spacing to my new eyes   Actually  I am wondering why C   doesn t employ lowercase null much like it employes lowercase false and true now

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I think the standard guarantees that NULL    0  so you can do either   I prefer NULL because it documents your intent

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I stopped using NULL in favor of 0 long ago  as well as as most other macros   I did this not only because I wanted to avoid macros as much as possible  but also because NULL seems to have become over-used in C and C   code  It seems to be used whenever a 0 value is needed  not just for pointers   On new projects  I put this in a project header   static const int nullptr   0    Now  when C  0x compliant compilers arrive  all I have to do is remove that line  A nice benefit of this is that Visual Studio already recognizes nullptr as a keyword and highlights it appropriately

User · Answer

I usually use 0  I don t like macros  and there s no guarantee that some third party header you re using doesn t redefine NULL to be something odd   You could use a nullptr object as proposed by Scott Meyers and others until C   gets a nullptr keyword   const    It is a const object    class nullptr t    public      template lt class T gt      operator T    const    convertible to any type of null non-member pointer          return 0         template lt class C  class T gt      operator T C      const      or any type of null member pointer          return 0     private      void operator amp    const      Can t take address of nullptr    nullptr         Google  nullptr  for more info

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I m with Stroustrup on this one  -  Since NULL is not part of the language  I prefer to use 0

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I think the standard guarantees that NULL    0  so you can do either   I prefer NULL because it documents your intent

User · Answer

I once worked on a machine where 0 was a valid address and NULL was defined as a special octal value   On that machine  0    NULL   so code such as  char  p        if  p            would not work as you expect   You HAD to write   if  p    NULL            Although I believe most compilers define NULL as 0 these days I still remember the lesson from those years ago   NULL is not necessarily 0

User · Answer

If I recall correctly NULL is defined differently in the headers that I have used  For C it is defined as  void  0  and for C   it s defines as just 0  The code looked something like    ifndef   cplusplus  define NULL  void  0  else  define NULL 0  endif   Personally I still use the NULL value to represent null pointers  it makes it explicit that you re using a pointer rather than some integral type  Yes internally the NULL value is still 0 but it isn t represented as such    Additionally I don t rely on the automatic conversion of integers to boolean values but explicitly compare them   For example prefer to use   if  pointer value    NULL    integer value    0    rather than   if  pointer value     integer value      Suffice to say that this is all remedied in C  11 where one can simply use nullptr instead of NULL  and also nullptr t that is the type of a nullptr

User · Answer

I once worked on a machine where 0 was a valid address and NULL was defined as a special octal value   On that machine  0    NULL   so code such as  char  p        if  p            would not work as you expect   You HAD to write   if  p    NULL            Although I believe most compilers define NULL as 0 these days I still remember the lesson from those years ago   NULL is not necessarily 0

User · Answer

If I recall correctly NULL is defined differently in the headers that I have used  For C it is defined as  void  0  and for C   it s defines as just 0  The code looked something like    ifndef   cplusplus  define NULL  void  0  else  define NULL 0  endif   Personally I still use the NULL value to represent null pointers  it makes it explicit that you re using a pointer rather than some integral type  Yes internally the NULL value is still 0 but it isn t represented as such    Additionally I don t rely on the automatic conversion of integers to boolean values but explicitly compare them   For example prefer to use   if  pointer value    NULL    integer value    0    rather than   if  pointer value     integer value      Suffice to say that this is all remedied in C  11 where one can simply use nullptr instead of NULL  and also nullptr t that is the type of a nullptr

[c++] Do you use NULL or 0 (zero) for pointers in C++?

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