error NULL was not declared in this scope

Question

I get this message when compiling C   on gcc 4 3  error     NULL    was not declared in this scope   It appears and disappears and I don t know why  Why   Thanks

User · Answer

To complete the other answers  If you are using C  11  use nullptr  which is a keyword that means a void pointer pointing to null   instead of NULL  which is not a pointer type

User · Answer

NULL isn t a keyword  it s a macro substitution for 0  and comes in stddef h or cstddef  I believe   You haven t  included an appropriate header file  so g   sees NULL as a regular variable name  and you haven t declared it

User · Answer

GCC is taking steps towards C  11  which is probably why you now need to include cstddef in order to use the NULL constant  The preferred way in C  11 is to use the new nullptr keyword  which is implemented in GCC since version 4 6  nullptr is not implicitly convertible to integral types  so it can be used to disambiguate a call to a function which has been overloaded for both pointer and integral types   void f int x   void f void   ptr    f 0       Passes int 0  f nullptr       Passes void   0

User · Answer

NULL is not a keyword  It s an identifier defined in some standard headers  You can include    include  lt cstddef gt    To have it in scope  including some other basics  like std  size t

User · Answer

To complete the other answers  If you are using C  11  use nullptr  which is a keyword that means a void pointer pointing to null   instead of NULL  which is not a pointer type

User · Answer

NULL is not a keyword  It s an identifier defined in some standard headers  You can include    include  lt cstddef gt    To have it in scope  including some other basics  like std  size t

User · Answer

NULL can also be found in     include  lt string h gt    String h will pull in the NULL from somewhere else

User · Answer

NULL isn t a keyword  it s a macro substitution for 0  and comes in stddef h or cstddef  I believe   You haven t  included an appropriate header file  so g   sees NULL as a regular variable name  and you haven t declared it

User · Answer

You can declare the macro NULL  Add that after your  includes    define NULL 0   or   ifndef NULL  define NULL 0  endif   No     at the end of the instructions

User · Answer

NULL is not a keyword  It s an identifier defined in some standard headers  You can include    include  lt cstddef gt    To have it in scope  including some other basics  like std  size t

User · Answer

NULL isn t a keyword  it s a macro substitution for 0  and comes in stddef h or cstddef  I believe   You haven t  included an appropriate header file  so g   sees NULL as a regular variable name  and you haven t declared it

User · Answer

NULL can also be found in     include  lt string h gt    String h will pull in the NULL from somewhere else

User · Answer

NULL isn t a keyword  it s a macro substitution for 0  and comes in stddef h or cstddef  I believe   You haven t  included an appropriate header file  so g   sees NULL as a regular variable name  and you haven t declared it

User · Answer

NULL is not a keyword  It s an identifier defined in some standard headers  You can include    include  lt cstddef gt    To have it in scope  including some other basics  like std  size t

User · Answer

You can declare the macro NULL  Add that after your  includes    define NULL 0   or   ifndef NULL  define NULL 0  endif   No     at the end of the instructions

User · Answer

GCC is taking steps towards C  11  which is probably why you now need to include cstddef in order to use the NULL constant  The preferred way in C  11 is to use the new nullptr keyword  which is implemented in GCC since version 4 6  nullptr is not implicitly convertible to integral types  so it can be used to disambiguate a call to a function which has been overloaded for both pointer and integral types   void f int x   void f void   ptr    f 0       Passes int 0  f nullptr       Passes void   0

[c++] error: ‘NULL’ was not declared in this scope

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