How can I use an array of function pointers

Question

How should I use array of function pointers in C   How can I initialize them

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You have a good example here  Array of Function pointers   with the syntax detailed   int sum int a  int b   int subtract int a  int b   int mul int a  int b   int div int a  int b    int   p 4    int x  int y    int main void      int result    int i  j  op     p 0    sum     address of sum        p 1    subtract     address of subtract        p 2    mul     address of mul        p 3    div     address of div              To call one of those function pointers   result     p op    i  j      op being the index of one of the four functions

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The simplest solution is to give the address of the final vector you want   and modify it inside the function     void calculation double result         do the calculation on result     result 0    10 5     result 1    10  6              int main         double result 10     0     this is the vector of the results      calculation result      this will modify result

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Can use it in the way like this       Define   define F NUM 3 int   pFunctions F NUM   void   arg        Initialise  int someFunction void   arg        int a     int  arg       return a a     pFunctions 0   someFunction       Use  int someMethod int idx  void   arg  int   result        int done  0      if  idx  lt  F NUM  amp  amp  pFunctions idx     NULL             result  pFunctions idx  arg           done  1            return done     int x  2  int z  0  someMethod 0   void   amp x   amp z   assert z    4

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This question has been already answered with very good examples  The only example that might be missing is one where the functions return pointers  I wrote another example with this  and added lots of comments  in case someone finds it helpful    include  lt stdio h gt   char   func1 char  a         a    b       return a     char   func2 char  a         a    c       return a     int main         char a    a          declare array of function pointers        the function pointer types are char   name char           A pointer to this type of function would be just        put   before name  and parenthesis around  name           char     name  char           An array of these pointers is the same with  x              char     functions 2   char       func1  func2       printf   c     a          the functions return a pointer  so I need to deference pointer        Thats why the   in front of the parenthesis  in case it confused you              printf   c        functions 0    amp a         printf   c n      functions 1    amp a         a    a          creating  name  for a function pointer type        funcp is equivalent to type char    funcname  char                typedef char    funcp  char            Now the declaration of the array of function pointers        becomes easier             funcp functions2 2     func1  func2        printf   c     a       printf   c        functions2 0    amp a        printf   c n      functions2 1    amp a         return 0

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Oh  there are tons of example  Just have a look at anything within glib or gtk  You can see the  work of function pointers in work there all the way    Here e g the initialization of the gtk button stuff    static void gtk button class init  GtkButtonClass  klass      GObjectClass  gobject class    GtkObjectClass  object class    GtkWidgetClass  widget class    GtkContainerClass  container class     gobject class   G OBJECT CLASS  klass     object class    GtkObjectClass   klass    widget class    GtkWidgetClass   klass    container class    GtkContainerClass   klass     gobject class- constructor   gtk button constructor    gobject class- set property   gtk button set property    gobject class- get property   gtk button get property     And in gtkobject h you find the following  declarations    struct  GtkObjectClass     GInitiallyUnownedClass parent class        Non overridable class methods to set and get per class arguments      void   set arg   GtkObject  object             GtkArg     arg             guint      arg id     void   get arg   GtkObject  object             GtkArg     arg             guint      arg id         Default signal handler for the   destroy signal  which is       invoked to request that references to the widget be dropped        If an object class overrides destroy   in order to perform class       specific destruction then it must still invoke its superclass        implementation of the method after it is finished with its       own cleanup   See gtk widget real destroy   for an example of       how to do this           void   destroy    GtkObject  object        The   set arg  stuff is a pointer to function and this can e g be assigned another implementation in some derived class   Often you see something like this  struct function table      char  name     void   some fun  int arg1  double arg2       void function1 int  arg1  double arg2        struct function table my table              function1   function1         So you can reach into the table by name and call the  associated  function    Or maybe you use a hash table in which you put the function and call it  by name    Regards  Friedrich

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This  answer  is more of an addendum to VonC s answer  just noting that the syntax can be simplified via a typedef  and aggregate initialization can be used   typedef int FUNC int  int    FUNC sum  subtract  mul  div  FUNC  p 4      sum  subtract  mul  div     int main void        int result      int i   2  j   3  op   2      2  mul      result   p op  i  j          6       maybe even in another file int sum int a  int b    return a b    int subtract int a  int b    return a-b    int mul int a  int b    return a b    int div int a  int b    return a b

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This should be a short  amp  simple copy  amp  paste piece of code example of the above responses  Hopefully this helps    include  lt iostream gt  using namespace std    define DBG PRINT x  do   std  printf  Line  -4d      15s    -10d n     LINE     x  x     while 0    void F0    printf  Print F d n   0     void F1    printf  Print F d n   1     void F2    printf  Print F d n   2     void F3    printf  Print F d n   3     void F4    printf  Print F d n   4     void   fArrVoid N FUNC        F0  F1  F2  F3  F4    int Sum int a  int b   return a b     int Sub int a  int b   return a-b     int Mul int a  int b   return a b     int Div int a  int b   return a b     int   fArrArgs 4   int a  int b     Sum  Sub  Mul  Div    int main        for int i   0  i  lt  5  i       fArrVoid i          printf   n         DBG PRINT   fArrArgs 0   3 2       DBG PRINT   fArrArgs 1   3 2       DBG PRINT   fArrArgs 2   3 2       DBG PRINT   fArrArgs 3   3 2        return 0

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Here s how you can use it   New Fun h   ifndef NEW FUN H   define NEW FUN H    include  lt stdio h gt   typedef int speed  speed fun int x    enum fp       f1  f2  f3  f4  f5     void F1    void F2    void F3    void F4    void F5     endif   New Fun c   include  New Fun h   speed fun int x        int Vel      Vel   x      return Vel     void F1         printf  From F1 n       void F2         printf  From F2 n       void F3         printf  From F3 n       void F4         printf  From F4 n       void F5         printf  From F5 n        Main c   include  lt stdio h gt   include  New Fun h   int main         int   F P  int y       void   F A 5         F1  F2  F3  F4  F5          if it is int the pointer incompatible is bound to happen     int xyz  i       printf  Hello Function Pointer  n        F P   fun      xyz   F P 5       printf  The Value is  d n   xyz           F A 5       F1  F2  F3  F4  F5        for  i   0  i  lt  5  i                  F A i               printf   n n        F A f1         F A f2         F A f3         F A f4         return 0      I hope this helps in understanding Function Pointer

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The above answers may help you but you may also want to know how to use array of function pointers   void fun1         void fun2         void fun3         void   func ptr 3        fun1  fun2  fun3    main         int option        printf   nEnter function number you want        printf   nYou should not enter other than 0   1  2       because we have only 3 functions        scanf   d   amp option        if  option gt  0  amp  amp  option lt  2                    func ptr option                 return 0      You can only assign the addresses of functions with the same return type and same argument types and no of arguments to a single function pointer array   You can also pass arguments like below if all the above functions are having the same number of arguments of same type       func ptr option   argu1     Note  here in the array the numbering of the function pointers will be starting from 0 same as in general arrays  So in above example fun1 can be called if option 0  fun2 can be called if option 1 and fun3 can be called if option 2

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The above answers may help you but you may also want to know how to use array of function pointers   void fun1         void fun2         void fun3         void   func ptr 3        fun1  fun2  fun3    main         int option        printf   nEnter function number you want        printf   nYou should not enter other than 0   1  2       because we have only 3 functions        scanf   d   amp option        if  option gt  0  amp  amp  option lt  2                    func ptr option                 return 0      You can only assign the addresses of functions with the same return type and same argument types and no of arguments to a single function pointer array   You can also pass arguments like below if all the above functions are having the same number of arguments of same type       func ptr option   argu1     Note  here in the array the numbering of the function pointers will be starting from 0 same as in general arrays  So in above example fun1 can be called if option 0  fun2 can be called if option 1 and fun3 can be called if option 2

User · Answer

Can use it in the way like this       Define   define F NUM 3 int   pFunctions F NUM   void   arg        Initialise  int someFunction void   arg        int a     int  arg       return a a     pFunctions 0   someFunction       Use  int someMethod int idx  void   arg  int   result        int done  0      if  idx  lt  F NUM  amp  amp  pFunctions idx     NULL             result  pFunctions idx  arg           done  1            return done     int x  2  int z  0  someMethod 0   void   amp x   amp z   assert z    4

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This simple example for multidimensional array with function pointers    void one  int a  int b      printf    n  ONE    a     d   b    d  a b    void two  int a  int b      printf    n  TWO    a     d   b    d  a b    void three  int a  int b      printf   n   THREE    a     d   b    d  a b    void four  int a  int b      printf    n  FOUR    a     d   b    d  a b    void five  int a  int b      printf    n   FIVE    a     d   b    d  a b    void  p 2  2   int int      int main         int i j      printf  multidimensional array with function pointers n         p 0  0    one     p 0  1    two     p 1  0    three     p 1  1    four      for    i    1   i  gt  0  i--          for    j    0   j  lt 2  j                  p i  j     i  i j       return 0

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Oh  there are tons of example  Just have a look at anything within glib or gtk  You can see the  work of function pointers in work there all the way    Here e g the initialization of the gtk button stuff    static void gtk button class init  GtkButtonClass  klass      GObjectClass  gobject class    GtkObjectClass  object class    GtkWidgetClass  widget class    GtkContainerClass  container class     gobject class   G OBJECT CLASS  klass     object class    GtkObjectClass   klass    widget class    GtkWidgetClass   klass    container class    GtkContainerClass   klass     gobject class- constructor   gtk button constructor    gobject class- set property   gtk button set property    gobject class- get property   gtk button get property     And in gtkobject h you find the following  declarations    struct  GtkObjectClass     GInitiallyUnownedClass parent class        Non overridable class methods to set and get per class arguments      void   set arg   GtkObject  object             GtkArg     arg             guint      arg id     void   get arg   GtkObject  object             GtkArg     arg             guint      arg id         Default signal handler for the   destroy signal  which is       invoked to request that references to the widget be dropped        If an object class overrides destroy   in order to perform class       specific destruction then it must still invoke its superclass        implementation of the method after it is finished with its       own cleanup   See gtk widget real destroy   for an example of       how to do this           void   destroy    GtkObject  object        The   set arg  stuff is a pointer to function and this can e g be assigned another implementation in some derived class   Often you see something like this  struct function table      char  name     void   some fun  int arg1  double arg2       void function1 int  arg1  double arg2        struct function table my table              function1   function1         So you can reach into the table by name and call the  associated  function    Or maybe you use a hash table in which you put the function and call it  by name    Regards  Friedrich

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This simple example for multidimensional array with function pointers    void one  int a  int b      printf    n  ONE    a     d   b    d  a b    void two  int a  int b      printf    n  TWO    a     d   b    d  a b    void three  int a  int b      printf   n   THREE    a     d   b    d  a b    void four  int a  int b      printf    n  FOUR    a     d   b    d  a b    void five  int a  int b      printf    n   FIVE    a     d   b    d  a b    void  p 2  2   int int      int main         int i j      printf  multidimensional array with function pointers n         p 0  0    one     p 0  1    two     p 1  0    three     p 1  1    four      for    i    1   i  gt  0  i--          for    j    0   j  lt 2  j                  p i  j     i  i j       return 0

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Oh  there are tons of example  Just have a look at anything within glib or gtk  You can see the  work of function pointers in work there all the way    Here e g the initialization of the gtk button stuff    static void gtk button class init  GtkButtonClass  klass      GObjectClass  gobject class    GtkObjectClass  object class    GtkWidgetClass  widget class    GtkContainerClass  container class     gobject class   G OBJECT CLASS  klass     object class    GtkObjectClass   klass    widget class    GtkWidgetClass   klass    container class    GtkContainerClass   klass     gobject class- constructor   gtk button constructor    gobject class- set property   gtk button set property    gobject class- get property   gtk button get property     And in gtkobject h you find the following  declarations    struct  GtkObjectClass     GInitiallyUnownedClass parent class        Non overridable class methods to set and get per class arguments      void   set arg   GtkObject  object             GtkArg     arg             guint      arg id     void   get arg   GtkObject  object             GtkArg     arg             guint      arg id         Default signal handler for the   destroy signal  which is       invoked to request that references to the widget be dropped        If an object class overrides destroy   in order to perform class       specific destruction then it must still invoke its superclass        implementation of the method after it is finished with its       own cleanup   See gtk widget real destroy   for an example of       how to do this           void   destroy    GtkObject  object        The   set arg  stuff is a pointer to function and this can e g be assigned another implementation in some derived class   Often you see something like this  struct function table      char  name     void   some fun  int arg1  double arg2       void function1 int  arg1  double arg2        struct function table my table              function1   function1         So you can reach into the table by name and call the  associated  function    Or maybe you use a hash table in which you put the function and call it  by name    Regards  Friedrich

User · Answer

This should be a short  amp  simple copy  amp  paste piece of code example of the above responses  Hopefully this helps    include  lt iostream gt  using namespace std    define DBG PRINT x  do   std  printf  Line  -4d      15s    -10d n     LINE     x  x     while 0    void F0    printf  Print F d n   0     void F1    printf  Print F d n   1     void F2    printf  Print F d n   2     void F3    printf  Print F d n   3     void F4    printf  Print F d n   4     void   fArrVoid N FUNC        F0  F1  F2  F3  F4    int Sum int a  int b   return a b     int Sub int a  int b   return a-b     int Mul int a  int b   return a b     int Div int a  int b   return a b     int   fArrArgs 4   int a  int b     Sum  Sub  Mul  Div    int main        for int i   0  i  lt  5  i       fArrVoid i          printf   n         DBG PRINT   fArrArgs 0   3 2       DBG PRINT   fArrArgs 1   3 2       DBG PRINT   fArrArgs 2   3 2       DBG PRINT   fArrArgs 3   3 2        return 0

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Oh  there are tons of example  Just have a look at anything within glib or gtk  You can see the  work of function pointers in work there all the way    Here e g the initialization of the gtk button stuff    static void gtk button class init  GtkButtonClass  klass      GObjectClass  gobject class    GtkObjectClass  object class    GtkWidgetClass  widget class    GtkContainerClass  container class     gobject class   G OBJECT CLASS  klass     object class    GtkObjectClass   klass    widget class    GtkWidgetClass   klass    container class    GtkContainerClass   klass     gobject class- constructor   gtk button constructor    gobject class- set property   gtk button set property    gobject class- get property   gtk button get property     And in gtkobject h you find the following  declarations    struct  GtkObjectClass     GInitiallyUnownedClass parent class        Non overridable class methods to set and get per class arguments      void   set arg   GtkObject  object             GtkArg     arg             guint      arg id     void   get arg   GtkObject  object             GtkArg     arg             guint      arg id         Default signal handler for the   destroy signal  which is       invoked to request that references to the widget be dropped        If an object class overrides destroy   in order to perform class       specific destruction then it must still invoke its superclass        implementation of the method after it is finished with its       own cleanup   See gtk widget real destroy   for an example of       how to do this           void   destroy    GtkObject  object        The   set arg  stuff is a pointer to function and this can e g be assigned another implementation in some derived class   Often you see something like this  struct function table      char  name     void   some fun  int arg1  double arg2       void function1 int  arg1  double arg2        struct function table my table              function1   function1         So you can reach into the table by name and call the  associated  function    Or maybe you use a hash table in which you put the function and call it  by name    Regards  Friedrich

User · Answer

The above answers may help you but you may also want to know how to use array of function pointers   void fun1         void fun2         void fun3         void   func ptr 3        fun1  fun2  fun3    main         int option        printf   nEnter function number you want        printf   nYou should not enter other than 0   1  2       because we have only 3 functions        scanf   d   amp option        if  option gt  0  amp  amp  option lt  2                    func ptr option                 return 0      You can only assign the addresses of functions with the same return type and same argument types and no of arguments to a single function pointer array   You can also pass arguments like below if all the above functions are having the same number of arguments of same type       func ptr option   argu1     Note  here in the array the numbering of the function pointers will be starting from 0 same as in general arrays  So in above example fun1 can be called if option 0  fun2 can be called if option 1 and fun3 can be called if option 2

User · Answer

The simplest solution is to give the address of the final vector you want   and modify it inside the function     void calculation double result         do the calculation on result     result 0    10 5     result 1    10  6              int main         double result 10     0     this is the vector of the results      calculation result      this will modify result

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This question has been already answered with very good examples  The only example that might be missing is one where the functions return pointers  I wrote another example with this  and added lots of comments  in case someone finds it helpful    include  lt stdio h gt   char   func1 char  a         a    b       return a     char   func2 char  a         a    c       return a     int main         char a    a          declare array of function pointers        the function pointer types are char   name char           A pointer to this type of function would be just        put   before name  and parenthesis around  name           char     name  char           An array of these pointers is the same with  x              char     functions 2   char       func1  func2       printf   c     a          the functions return a pointer  so I need to deference pointer        Thats why the   in front of the parenthesis  in case it confused you              printf   c        functions 0    amp a         printf   c n      functions 1    amp a         a    a          creating  name  for a function pointer type        funcp is equivalent to type char    funcname  char                typedef char    funcp  char            Now the declaration of the array of function pointers        becomes easier             funcp functions2 2     func1  func2        printf   c     a       printf   c        functions2 0    amp a        printf   c n      functions2 1    amp a         return 0

User · Answer

The above answers may help you but you may also want to know how to use array of function pointers   void fun1         void fun2         void fun3         void   func ptr 3        fun1  fun2  fun3    main         int option        printf   nEnter function number you want        printf   nYou should not enter other than 0   1  2       because we have only 3 functions        scanf   d   amp option        if  option gt  0  amp  amp  option lt  2                    func ptr option                 return 0      You can only assign the addresses of functions with the same return type and same argument types and no of arguments to a single function pointer array   You can also pass arguments like below if all the above functions are having the same number of arguments of same type       func ptr option   argu1     Note  here in the array the numbering of the function pointers will be starting from 0 same as in general arrays  So in above example fun1 can be called if option 0  fun2 can be called if option 1 and fun3 can be called if option 2

User · Answer

This  answer  is more of an addendum to VonC s answer  just noting that the syntax can be simplified via a typedef  and aggregate initialization can be used   typedef int FUNC int  int    FUNC sum  subtract  mul  div  FUNC  p 4      sum  subtract  mul  div     int main void        int result      int i   2  j   3  op   2      2  mul      result   p op  i  j          6       maybe even in another file int sum int a  int b    return a b    int subtract int a  int b    return a-b    int mul int a  int b    return a b    int div int a  int b    return a b

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Here s how you can use it   New Fun h   ifndef NEW FUN H   define NEW FUN H    include  lt stdio h gt   typedef int speed  speed fun int x    enum fp       f1  f2  f3  f4  f5     void F1    void F2    void F3    void F4    void F5     endif   New Fun c   include  New Fun h   speed fun int x        int Vel      Vel   x      return Vel     void F1         printf  From F1 n       void F2         printf  From F2 n       void F3         printf  From F3 n       void F4         printf  From F4 n       void F5         printf  From F5 n        Main c   include  lt stdio h gt   include  New Fun h   int main         int   F P  int y       void   F A 5         F1  F2  F3  F4  F5          if it is int the pointer incompatible is bound to happen     int xyz  i       printf  Hello Function Pointer  n        F P   fun      xyz   F P 5       printf  The Value is  d n   xyz           F A 5       F1  F2  F3  F4  F5        for  i   0  i  lt  5  i                  F A i               printf   n n        F A f1         F A f2         F A f3         F A f4         return 0      I hope this helps in understanding Function Pointer

User · Answer

You have a good example here  Array of Function pointers   with the syntax detailed   int sum int a  int b   int subtract int a  int b   int mul int a  int b   int div int a  int b    int   p 4    int x  int y    int main void      int result    int i  j  op     p 0    sum     address of sum        p 1    subtract     address of subtract        p 2    mul     address of mul        p 3    div     address of div              To call one of those function pointers   result     p op    i  j      op being the index of one of the four functions

User · Answer

You have a good example here  Array of Function pointers   with the syntax detailed   int sum int a  int b   int subtract int a  int b   int mul int a  int b   int div int a  int b    int   p 4    int x  int y    int main void      int result    int i  j  op     p 0    sum     address of sum        p 1    subtract     address of subtract        p 2    mul     address of mul        p 3    div     address of div              To call one of those function pointers   result     p op    i  j      op being the index of one of the four functions

User · Answer

You have a good example here  Array of Function pointers   with the syntax detailed   int sum int a  int b   int subtract int a  int b   int mul int a  int b   int div int a  int b    int   p 4    int x  int y    int main void      int result    int i  j  op     p 0    sum     address of sum        p 1    subtract     address of subtract        p 2    mul     address of mul        p 3    div     address of div              To call one of those function pointers   result     p op    i  j      op being the index of one of the four functions

[c] How can I use an array of function pointers?

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