FOR EACH ... NEXT, ¿ Que es ? y ¿ Para que se usa ?

[JmGarcia]

Code: Select all

FOR EACH <element> IN <array>|<object>|<string>
   <statements>
   [LOOP]
   <statements>
   [EXIT]
NEXT

Debido a mi poca "sapiencia" del idioma ingles... alguien podría explicarme para que es y para que sirve la clausula FOR EACH ... NEXT

Algún ejejmplito seria interesante.

Gracias.

[metaldrummer]

No me di el tiempo de traducirlo. Espero esto te sirva.
FOR EACH
Iterates elements of data types that can be seen as a collection.
Syntax
FOR EACH <element> IN <array>|<object>|<string>
<statements>
[LOOP]
<statements>
[EXIT]
NEXT

Arguments
<element>
The name of a variable that gets assigned a new value on each iteration.
IN <array>
This is a value of data type Array. The FOR EACH loop iterates all array elements in the first dimension and assigns their values to <element>.
IN <object>
This is a value of data type Object. The FOR EACH loop iterates all instance variables of the object and assigns their values to <element>.
IN <string>
This is a value of data type Character string. The FOR EACH loop iterates all individual characters of the string and assigns them to <element>.
LOOP
The LOOP statement unconditionally branches to the FOR EACH statement, i.e. to the begin of the loop, where the next value is assigned to <element>.
EXIT
The EXIT statement unconditionally terminates the FOR EACH loop and branches to the statement following NEXT. Description
The FOR EACH statement forms a control structure that executes a block of statements for a data type containing multiple elements. This can be data of type Array, Object or Character string. The loop iterates all elements contained in the data and assigns the value of the next element to <element> on each iteration.
FOR EACH is similar to the regular FOR loop. But it completes considerably faster than a FOR loop, since there is no explicit loop counter. In contrast, FOR EACH uses an implicit loop counter whose value can be queried using the function HB_EnumIndex(). Other than this, LOOP and EXIT statements within the loop are treated the same as in a FOR loop.
When FOR EACH statements are nested, each loop maintains its own counter, i.e. HB_EnumIndex() retrieves the counter of the loop that is currently executed. When the FOR EACH loop is finished, its loop counter is set to 0.

Example
// The example demonstrates the FOR EACH statement using two
// nested loops. The outer loop iterates an array while the
// inner loop iterates character strings.

Code: Select all

PROCEDURE Main()
      LOCAL aArray := { "Hello", "World" }
      LOCAL cString, cChar

      FOR EACH cString IN aArray
         ? "----- Outer loop -----"
         ? HB_EnumIndex(), cString

         ? "----- Inner loop -----"
         FOR EACH cChar IN cSTring
            ? HB_EnumIndex(), cChar
         NEXT
      NEXT

      ? "-------- End ---------"
      ? HB_EnumIndex()
   RETURN

/* Output of example:
----- Outer loop -----
1 Hello
----- Inner loop -----
1 H
2 e
3 l
4 l
5 o
----- Outer loop -----
2 World
----- Inner loop -----
1 W
2 o
3 r
4 l
5 d
-------- End ---------
0
*/

Saludos

[Antonio Linares]

JM,

Te permite simplificar el recorrido por cada uno de los elementos de un array (ó de las DATAs de un objeto, ó de una cadena): No hay que usar una variable temporal ni usar el índice del elemento del array.