Does C have a foreach loop construct

Question

Almost all languages have a foreach loop or something similar  Does C have one  Can you post some example code

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While C does not have a for each construct  it has always had an idiomatic representation for one past the end of an array   amp arr  1   This allows you to write a simple idiomatic for each loop as follows   int arr      1 2 3 4 5   for int  a   arr  a  lt    amp arr  1     a      printf   d n    a

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C has  for  and  while  keywords  If a foreach statement in a language like C  looks like this      foreach  Element element in collection            then the equivalent of this foreach statement in C might be be like   for       Element  element   GetFirstElement  amp collection       element    0      element   GetNextElement  amp collection  element                TODO  do something with this element instance

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While C does not have a for each construct  it has always had an idiomatic representation for one past the end of an array   amp arr  1   This allows you to write a simple idiomatic for each loop as follows   int arr      1 2 3 4 5   for int  a   arr  a  lt    amp arr  1     a      printf   d n    a

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There is no foreach in C   You can use a for loop to loop through the data but the length needs to be know or the data needs to be terminated by a know value  eg  null    char  nullTerm  nullTerm    Loop through my characters    for  nullTerm    NULL nullTerm            nullTerm will now point to the next character

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There is no foreach in C   You can use a for loop to loop through the data but the length needs to be know or the data needs to be terminated by a know value  eg  null    char  nullTerm  nullTerm    Loop through my characters    for  nullTerm    NULL nullTerm            nullTerm will now point to the next character

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C doesn t have a foreach  but macros are frequently used to emulate that    define for each item item  list        for T   item   list- gt head  item    NULL  item   item- gt next    And can be used like  for each item i  processes        i- gt wakeup        Iteration over an array is also possible    define foreach item  array        for int keep   1                count   0               size   sizeof  array    sizeof   array             keep  amp  amp  count    size            keep    keep  count            for item    array    count  keep  keep    keep    And can be used like  int values       1  2  3    foreach int  v  values        printf  value   d n    v       Edit  In case you are also interested in C   solutions  C   has a native for-each syntax called  range based for

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This is a fairly old question  but I though I should post this  It is a foreach loop for GNU C99    include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   include  lt stdbool h gt    define FOREACH COMP INDEX  ARRAY  ARRAY TYPE  SIZE        extension                bool ret   0        if    builtin types compatible p  const char   ARRAY TYPE           ret   INDEX  lt  strlen   const char  ARRAY         else         ret   INDEX  lt  SIZE        ret           define FOREACH ELEM INDEX  ARRAY  TYPE        extension                TYPE  tmp array    ARRAY         amp tmp array  INDEX            define FOREACH VAR  ARRAY    for  void  array     void   ARRAY   array   array    0    for  size t i    0  i   amp  amp  array   amp  amp  FOREACH COMP  i   array                                           typeof    ARRAY                                         sizeof  ARRAY    sizeof   ARRAY  0                                           i       for  bool b    1  b    b     array    0   0  b    0    for  VAR   FOREACH ELEM  i   array     typeof     ARRAY  0     b   b    0      example s    int main  int argc  char   argv      int array 10        initialize the array      int i   0    FOREACH  int  x  array               x   i          i           char  str    hello  world      FOREACH  char  c  str      printf    c n    c      return EXIT SUCCESS      This code has been tested to work with gcc  icc and clang on GNU Linux

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This is a fairly old question  but I though I should post this  It is a foreach loop for GNU C99    include  lt stdio h gt   include  lt stdlib h gt   include  lt string h gt   include  lt stdbool h gt    define FOREACH COMP INDEX  ARRAY  ARRAY TYPE  SIZE        extension                bool ret   0        if    builtin types compatible p  const char   ARRAY TYPE           ret   INDEX  lt  strlen   const char  ARRAY         else         ret   INDEX  lt  SIZE        ret           define FOREACH ELEM INDEX  ARRAY  TYPE        extension                TYPE  tmp array    ARRAY         amp tmp array  INDEX            define FOREACH VAR  ARRAY    for  void  array     void   ARRAY   array   array    0    for  size t i    0  i   amp  amp  array   amp  amp  FOREACH COMP  i   array                                           typeof    ARRAY                                         sizeof  ARRAY    sizeof   ARRAY  0                                           i       for  bool b    1  b    b     array    0   0  b    0    for  VAR   FOREACH ELEM  i   array     typeof     ARRAY  0     b   b    0      example s    int main  int argc  char   argv      int array 10        initialize the array      int i   0    FOREACH  int  x  array               x   i          i           char  str    hello  world      FOREACH  char  c  str      printf    c n    c      return EXIT SUCCESS      This code has been tested to work with gcc  icc and clang on GNU Linux

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Here s a simple one  single for loop    define FOREACH type  array  size  do             type it   array 0             for int i   0  i  lt  size  i    it   array i    define ENDFOR    while 0    int array       1  2  3  4  5     FOREACH int  array  5        printf  element   d  index   d n   it  i     ENDFOR   Gives you access to the index should you want it  i  and the current item we re iterating over  it   Note you might have naming issues when nesting loops  you can make the item and index names be parameters to the macro   Edit  Here s a modified version of the accepted answer foreach  Lets you specify the start index  the size so that it works on decayed arrays  pointers   no need for int  and changed count    size to i  lt  size just in case the user accidentally modifies  i  to be bigger than size and get stuck in an infinite loop    define FOREACH item  array  start  size       for int i   start  keep   1           keep  amp  amp  i  lt  size           keep    keep  i         for  item   array i   keep  keep    keep   int array       1  2  3  4  5    FOREACH int x  array  2  5      printf  index   d  element   d n   i  x     Output   index  2  element  3 index  3  element  4 index  4  element  5

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Eric s answer doesn t work when you re using  break  or  continue     This can be fixed by rewriting the first line   Original line  reformatted    for  unsigned i   0    a   1  i  lt  B size    i      a   1    Fixed   for  unsigned i   0    a   1    a  amp  amp  i  lt  B size    i      a   1    If you compare it to Johannes  loop  you ll see that he s actually doing the same  just a bit more complicated and uglier

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C doesn t have a foreach  but macros are frequently used to emulate that    define for each item item  list        for T   item   list- gt head  item    NULL  item   item- gt next    And can be used like  for each item i  processes        i- gt wakeup        Iteration over an array is also possible    define foreach item  array        for int keep   1                count   0               size   sizeof  array    sizeof   array             keep  amp  amp  count    size            keep    keep  count            for item    array    count  keep  keep    keep    And can be used like  int values       1  2  3    foreach int  v  values        printf  value   d n    v       Edit  In case you are also interested in C   solutions  C   has a native for-each syntax called  range based for

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C has  for  and  while  keywords  If a foreach statement in a language like C  looks like this      foreach  Element element in collection            then the equivalent of this foreach statement in C might be be like   for       Element  element   GetFirstElement  amp collection       element    0      element   GetNextElement  amp collection  element                TODO  do something with this element instance

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Here is what I use when I m stuck with C   You can t use the same item name twice in the same scope  but that s not really an issue since not all of us get to use nice new compilers      define FOREACH type  item  array  size        size t X keep   X i         type item        for  X keep    1  X i    0   X i   lt   size   X keep     X keep   X i               for  item    array  X i    X keep   X keep    0    define  foreach item  array  FOREACH   typeof   array 0    item  array  length array    define foreach item in array   foreach item in array    define in    define length array   sizeof array    sizeof  array  0     define CAT a  b  CAT HELPER a  b     Concatenate two symbols for macros      define CAT HELPER a  b  a    b  define X name  CAT     name    LINE       unique variable      Usage   int ints      1  2  0  3  4   foreach  i in ints  printf   i   i      can t use the same name in this scope anymore     foreach  x in ints  printf   i   x     EDIT  Here is an alternative for FOREACH using the c99 syntax to avoid namespace pollution    define FOREACH type  item  array  size        for  size t X keep    1  X i    0  X i   lt   size   X keep    1  X i           for  type item    array  X i    X keep   X keep    0

User · Answer

C has  for  and  while  keywords  If a foreach statement in a language like C  looks like this      foreach  Element element in collection            then the equivalent of this foreach statement in C might be be like   for       Element  element   GetFirstElement  amp collection       element    0      element   GetNextElement  amp collection  element                TODO  do something with this element instance

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C does not have an implementation of for-each  When parsing an array as a point the receiver does not know how long the array is  thus there is no way to tell when you reach the end of the array   Remember  in C int  is a point to a memory address containing an int  There is no header object containing information about how many integers that are placed in sequence  Thus  the programmer needs to keep track of this   However  for lists  it is easy to implement something that resembles a for-each loop    for Node  node   head  node  node   node next          do your magic here        To achieve something similar for arrays you can do one of two things     use the first element to store the length of the array   wrap the array in a struct which holds the length and a pointer to the array    The following is an example of such struct   typedef struct job t      int count     int  arr    arr t

User · Answer

C doesn t have a foreach  but macros are frequently used to emulate that    define for each item item  list        for T   item   list- gt head  item    NULL  item   item- gt next    And can be used like  for each item i  processes        i- gt wakeup        Iteration over an array is also possible    define foreach item  array        for int keep   1                count   0               size   sizeof  array    sizeof   array             keep  amp  amp  count    size            keep    keep  count            for item    array    count  keep  keep    keep    And can be used like  int values       1  2  3    foreach int  v  values        printf  value   d n    v       Edit  In case you are also interested in C   solutions  C   has a native for-each syntax called  range based for

User · Answer

There is no foreach in C   You can use a for loop to loop through the data but the length needs to be know or the data needs to be terminated by a know value  eg  null    char  nullTerm  nullTerm    Loop through my characters    for  nullTerm    NULL nullTerm            nullTerm will now point to the next character

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Here is a full program example of a for-each macro in C99    include  lt stdio h gt   typedef struct list node list node  struct list node       list node  next      void  data       define FOR EACH item  list        for  list node   item     list    item    item     item - gt next   int main int argc  char  argv          list node list                  next    amp list 1    data    test 1                next    amp list 2    data    test 2                next   NULL       data    test 3                FOR EACH item  list          puts  char    item- gt data        return 0

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As you probably already know  there s no  quot foreach quot -style loop in C  Although there are already tons of great macros provided here to work around this  maybe you ll find this macro useful      quot length quot  is the length of the array      define each item  array  length     typeof   array    p    array    item     p  p  lt   amp   array  length    p     item     p      which can be used with for  as in for each         Advantages of this approach   item is declared and incremented within the for statement  just like in Python    Seems to work on any 1-dimensional array All variables created in macro  p  item   aren t visible outside the scope of the loop  since they re declared in the for loop header    Disadvantages   Doesn t work for multi-dimensional arrays Relies on typeof    which is a GNU extension  not part of standard C Since it declares variables in the for loop header  it only works in C11 or later   Just to save you some time  here s how you could test it  typedef struct       double x      double y    Point   int main void        double some nums      4 2  4 32  -9 9  7 0       for each  element  some nums  4          printf  quot element    lf n quot   element        int numbers      4  2  99  -3  54          Just demonstrating it can be used like a normal for loop     for each  number  numbers  5             printf  quot number    d n quot   number           if  number   2    0                  printf  quot  d is even  n quot   number              char  dictionary       quot Hello quot    quot World quot        for each  word  dictionary  2          printf  quot word     s  n quot   word        Point points       3 4  4 2    9 9  6 7    -9 8  7 0        for each  point  points  3          printf  quot point     lf   lf  n quot   point x  point y           Neither p  element  number or word are visible outside the scope of        their respective for loops  Try to see if these printfs work         they shouldn t          printf  quot  p    s quot    p          printf  quot word    s quot   word        return 0     Seems to work on gcc and clang by default  haven t tested other compilers

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Here is a full program example of a for-each macro in C99    include  lt stdio h gt   typedef struct list node list node  struct list node       list node  next      void  data       define FOR EACH item  list        for  list node   item     list    item    item     item - gt next   int main int argc  char  argv          list node list                  next    amp list 1    data    test 1                next    amp list 2    data    test 2                next   NULL       data    test 3                FOR EACH item  list          puts  char    item- gt data        return 0

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Eric s answer doesn t work when you re using  break  or  continue     This can be fixed by rewriting the first line   Original line  reformatted    for  unsigned i   0    a   1  i  lt  B size    i      a   1    Fixed   for  unsigned i   0    a   1    a  amp  amp  i  lt  B size    i      a   1    If you compare it to Johannes  loop  you ll see that he s actually doing the same  just a bit more complicated and uglier

User · Answer

Here is a full program example of a for-each macro in C99    include  lt stdio h gt   typedef struct list node list node  struct list node       list node  next      void  data       define FOR EACH item  list        for  list node   item     list    item    item     item - gt next   int main int argc  char  argv          list node list                  next    amp list 1    data    test 1                next    amp list 2    data    test 2                next   NULL       data    test 3                FOR EACH item  list          puts  char    item- gt data        return 0

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C doesn t have a foreach  but macros are frequently used to emulate that    define for each item item  list        for T   item   list- gt head  item    NULL  item   item- gt next    And can be used like  for each item i  processes        i- gt wakeup        Iteration over an array is also possible    define foreach item  array        for int keep   1                count   0               size   sizeof  array    sizeof   array             keep  amp  amp  count    size            keep    keep  count            for item    array    count  keep  keep    keep    And can be used like  int values       1  2  3    foreach int  v  values        printf  value   d n    v       Edit  In case you are also interested in C   solutions  C   has a native for-each syntax called  range based for

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If you re planning to work with function pointers   define lambda return type  function body          return type   fn   function body   fn         define array len arr   sizeof arr  sizeof arr 0      define foreachnf type  item  arr  arr length  func         void   action  type item    func       for  int i   0  i lt arr length  i    action arr i         define foreachf type  item  arr  func       foreachnf type  item  arr  array len arr   func    define foreachn type  item  arr  arr length  body       foreachnf type  item  arr  arr length  lambda void   type item  body     define foreach type  item  arr  body       foreachn type  item  arr  array len arr   body    Usage   int ints       1  2  3  4  5    foreach int  i  ints        printf   d n   i        char  strs        hi     hello      hello world    just    testing     foreach char   s  strs        printf   s n   s        char   strsp   malloc sizeof char   2   strsp 0     abcd   strsp 1     efgh   foreachn char   s  strsp  2        printf   s n   s        void   myfun  int i    somefunc  foreachf int  i  ints  myfun     But I think this will work only on gcc  not sure

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C does not have an implementation of for-each  When parsing an array as a point the receiver does not know how long the array is  thus there is no way to tell when you reach the end of the array   Remember  in C int  is a point to a memory address containing an int  There is no header object containing information about how many integers that are placed in sequence  Thus  the programmer needs to keep track of this   However  for lists  it is easy to implement something that resembles a for-each loop    for Node  node   head  node  node   node next          do your magic here        To achieve something similar for arrays you can do one of two things     use the first element to store the length of the array   wrap the array in a struct which holds the length and a pointer to the array    The following is an example of such struct   typedef struct job t      int count     int  arr    arr t

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Here is what I use when I m stuck with C   You can t use the same item name twice in the same scope  but that s not really an issue since not all of us get to use nice new compilers      define FOREACH type  item  array  size        size t X keep   X i         type item        for  X keep    1  X i    0   X i   lt   size   X keep     X keep   X i               for  item    array  X i    X keep   X keep    0    define  foreach item  array  FOREACH   typeof   array 0    item  array  length array    define foreach item in array   foreach item in array    define in    define length array   sizeof array    sizeof  array  0     define CAT a  b  CAT HELPER a  b     Concatenate two symbols for macros      define CAT HELPER a  b  a    b  define X name  CAT     name    LINE       unique variable      Usage   int ints      1  2  0  3  4   foreach  i in ints  printf   i   i      can t use the same name in this scope anymore     foreach  x in ints  printf   i   x     EDIT  Here is an alternative for FOREACH using the c99 syntax to avoid namespace pollution    define FOREACH type  item  array  size        for  size t X keep    1  X i    0  X i   lt   size   X keep    1  X i           for  type item    array  X i    X keep   X keep    0

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As you probably already know  there s no  quot foreach quot -style loop in C  Although there are already tons of great macros provided here to work around this  maybe you ll find this macro useful      quot length quot  is the length of the array      define each item  array  length     typeof   array    p    array    item     p  p  lt   amp   array  length    p     item     p      which can be used with for  as in for each         Advantages of this approach   item is declared and incremented within the for statement  just like in Python    Seems to work on any 1-dimensional array All variables created in macro  p  item   aren t visible outside the scope of the loop  since they re declared in the for loop header    Disadvantages   Doesn t work for multi-dimensional arrays Relies on typeof    which is a GNU extension  not part of standard C Since it declares variables in the for loop header  it only works in C11 or later   Just to save you some time  here s how you could test it  typedef struct       double x      double y    Point   int main void        double some nums      4 2  4 32  -9 9  7 0       for each  element  some nums  4          printf  quot element    lf n quot   element        int numbers      4  2  99  -3  54          Just demonstrating it can be used like a normal for loop     for each  number  numbers  5             printf  quot number    d n quot   number           if  number   2    0                  printf  quot  d is even  n quot   number              char  dictionary       quot Hello quot    quot World quot        for each  word  dictionary  2          printf  quot word     s  n quot   word        Point points       3 4  4 2    9 9  6 7    -9 8  7 0        for each  point  points  3          printf  quot point     lf   lf  n quot   point x  point y           Neither p  element  number or word are visible outside the scope of        their respective for loops  Try to see if these printfs work         they shouldn t          printf  quot  p    s quot    p          printf  quot word    s quot   word        return 0     Seems to work on gcc and clang by default  haven t tested other compilers

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Here s a simple one  single for loop    define FOREACH type  array  size  do             type it   array 0             for int i   0  i  lt  size  i    it   array i    define ENDFOR    while 0    int array       1  2  3  4  5     FOREACH int  array  5        printf  element   d  index   d n   it  i     ENDFOR   Gives you access to the index should you want it  i  and the current item we re iterating over  it   Note you might have naming issues when nesting loops  you can make the item and index names be parameters to the macro   Edit  Here s a modified version of the accepted answer foreach  Lets you specify the start index  the size so that it works on decayed arrays  pointers   no need for int  and changed count    size to i  lt  size just in case the user accidentally modifies  i  to be bigger than size and get stuck in an infinite loop    define FOREACH item  array  start  size       for int i   start  keep   1           keep  amp  amp  i  lt  size           keep    keep  i         for  item   array i   keep  keep    keep   int array       1  2  3  4  5    FOREACH int x  array  2  5      printf  index   d  element   d n   i  x     Output   index  2  element  3 index  3  element  4 index  4  element  5

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There is no foreach in C   You can use a for loop to loop through the data but the length needs to be know or the data needs to be terminated by a know value  eg  null    char  nullTerm  nullTerm    Loop through my characters    for  nullTerm    NULL nullTerm            nullTerm will now point to the next character

User · Answer

C has  for  and  while  keywords  If a foreach statement in a language like C  looks like this      foreach  Element element in collection            then the equivalent of this foreach statement in C might be be like   for       Element  element   GetFirstElement  amp collection       element    0      element   GetNextElement  amp collection  element                TODO  do something with this element instance

User · Answer

If you re planning to work with function pointers   define lambda return type  function body          return type   fn   function body   fn         define array len arr   sizeof arr  sizeof arr 0      define foreachnf type  item  arr  arr length  func         void   action  type item    func       for  int i   0  i lt arr length  i    action arr i         define foreachf type  item  arr  func       foreachnf type  item  arr  array len arr   func    define foreachn type  item  arr  arr length  body       foreachnf type  item  arr  arr length  lambda void   type item  body     define foreach type  item  arr  body       foreachn type  item  arr  array len arr   body    Usage   int ints       1  2  3  4  5    foreach int  i  ints        printf   d n   i        char  strs        hi     hello      hello world    just    testing     foreach char   s  strs        printf   s n   s        char   strsp   malloc sizeof char   2   strsp 0     abcd   strsp 1     efgh   foreachn char   s  strsp  2        printf   s n   s        void   myfun  int i    somefunc  foreachf int  i  ints  myfun     But I think this will work only on gcc  not sure

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Here is a full program example of a for-each macro in C99    include  lt stdio h gt   typedef struct list node list node  struct list node       list node  next      void  data       define FOR EACH item  list        for  list node   item     list    item    item     item - gt next   int main int argc  char  argv          list node list                  next    amp list 1    data    test 1                next    amp list 2    data    test 2                next   NULL       data    test 3                FOR EACH item  list          puts  char    item- gt data        return 0

[c] Does C have a "foreach" loop construct?

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