topic Re: field symbolsc code in Application Development and Automation Discussions

field symbolsc code

Former Member — Fri, 25 May 2007 06:32:35 GMT

I have the following difficulties in the following code:-

REPORT demo_field_symbols_stat_ASSIGN .

FIELD-SYMBOLS: <f1> TYPE ANY, <f2> TYPE i.

DATA: text(20) TYPE c VALUE 'Hello, how are you?',

num TYPE i VALUE 5,

BEGIN OF line1,

col1 TYPE f VALUE '1.1e+10',

col2 TYPE i VALUE '1234',

END OF line1,

line2 LIKE line1.

ASSIGN text TO <f1>.

ASSIGN num TO <f2>.

DESCRIBE FIELD <f1> LENGTH <f2>.

WRITE: / <f1>, 'has length', num.

ASSIGN line1 TO <f1>.

ASSIGN line2-col2 TO <f2>.

MOVE <f1> TO line2.

ASSIGN 'LINE2-COL2 =' TO <f1>.

WRITE: / <f1>, <f2>.

The list output is:

Hello, how are you? has length 20

LINE-COL2 = 1,234

The example declares two field symbols <f1> and <f2>. <f2> may only have fields of type I since it has been typed accordingly. <f1> and <f2> both point to different fields during the program.

q1]] How does the "2" types of statements differentiates

i]ASSIGN <V> TO <FS>. Where <v > refers to any variable & <fs> to any field symbols

ii] MOVE <fs> TO <V>.

q2]] How does the "NUM" variable's presence affect the output in the write statement----what I mean by the question is what would have haooened if we had written <F2> instead of NUM ; min the following statements:-

ASSIGN text TO <f1>.

ASSIGN num TO <f2>.

DESCRIBE FIELD <f1> LENGTH <f2>.

WRITE: / <f1>, 'has length', num

Re: field symbolsc code

Former Member — Fri, 25 May 2007 06:37:25 GMT

Go through the documnetation and correct it

Field Symbols

Field symbols are placeholders or symbolic names for other fields. They do not physically reserve space for a field, but point to its contents. A field symbol cam point to any data object. The data object to which a field symbol points is assigned to it after it has been declared in the program.

Whenever you address a field symbol in a program, you are addressing the field that is assigned to the field symbol. After successful assignment, there is no difference in ABAP whether you reference the field symbol or the field itself. You must assign a field to each field symbol before you can address the latter in programs.

Field symbols are similar to dereferenced pointers in C (that is, pointers to which the content operator * is applied). However, the only real equivalent of pointers in ABAP, that is, variables that contain a memory address (reference) and that can be used without the contents operator, are reference variables in ABAP Objects.

All operations programmed with field symbols are applied to the field assigned to it. For example, a MOVE statement between two field symbols moves the contents of the field assigned to the first field symbol to the field assigned to the second field symbol. The field symbols themselves point to the same fields after the MOVE statement as they did before.

You can create field symbols either without or with type specifications. If you do not specify a type, the field symbol inherits all of the technical attributes of the field assigned to it. If you do specify a type, the system checks the compatibility of the field symbol and the field you are assigning to it during the ASSIGN statement.

Field symbols provide greater flexibility when you address data objects:

If you want to process sections of fields, you can specify the offset and length of the field dynamically.

You can assign one field symbol to another, which allows you to address parts of fields.

Assignments to field symbols may extend beyond field boundaries. This allows you to address regular sequences of fields in memory efficiently.

You can also force a field symbol to take different technical attributes from those of the field assigned to it.

The flexibility of field symbols provides elegant solutions to certain problems. On the other hand, it does mean that errors can easily occur. Since fields are not assigned to field symbols until runtime, the effectiveness of syntax and security checks is very limited for operations involving field symbols. This can lead to runtime errors or incorrect data assignments.

While runtime errors indicate an obvious problem, incorrect data assignments are dangerous because they can be very difficult to detect. For this reason, you should only use field symbols if you cannot achieve the same result using other ABAP statements.

For example, you may want to process part of a string where the offset and length depend on the contents of the field. You could use field symbols in this case. However, since the MOVE statement also supports variable offset and length specifications, you should use it instead. The MOVE statement (with your own auxiliary variables if required) is much safer than using field symbols, since it cannot address memory beyond the boundary of a field. However, field symbols may improve performance in some cases.

check the below links u will get the answers for your questions

http://help.sap.com/saphelp_nw04/helpdata/en/fc/eb3860358411d1829f0000e829fbfe/content.htm

http://www.sts.tu-harburg.de/teaching/sap_r3/ABAP4/field_sy.htm

http://searchsap.techtarget.com/tip/1,289483,sid21_gci920484,00.html

Syntax Diagram

FIELD-SYMBOLS

Basic form

FIELD-SYMBOLS <fs>.

Extras:

1. ... TYPE type

2. ... TYPE REF TO cif

3. ... TYPE REF TO DATA

4. ... TYPE LINE OF type

5. ... LIKE s

6. ... LIKE LINE OF s

7. ... TYPE tabkind

8. ... STRUCTURE s DEFAULT wa

The syntax check performed in an ABAP Objects context is stricter than in other ABAP areas. See Cannot Use Untyped Field Symbols ad Cannot Use Field Symbols as Components of Classes.

Effect

This statement declares a symbolic field called <fs>. At runtime, you can assign a concrete field to the field symbol using ASSIGN. All operations performed with the field symbol then directly affect the field assigned to it.

You can only use one of the additions.

Example

Output aircraft type from the table SFLIGHT using a field symbol:

FIELD-SYMBOLS <PT> TYPE ANY.

DATA SFLIGHT_WA TYPE SFLIGHT.

...

ASSIGN SFLIGHT_WA-PLANETYPE TO <PT>.

WRITE <PT>.

Addition 1

... TYPE type

Addition 2

... TYPE REF TO cif

Addition 3

... TYPE REF TO DATA

Addition 4

... TYPE LINE OF type

Addition 5

... LIKE s

Addition 6

... LIKE LINE OF s

Addition 7

... TYPE tabkind

Effect

You can define the type of the field symbol using additions 2 to 7 (just as you can for FORM parameters (compare Defining the Type of Subroutine Parameters). When you use the ASSIGN statement, the system carries out the same type checks as for USING parameters of FORMs.

This addition is not allowed in an ABAP Objects context. See Cannot Use Obsolete Casting for FIELD SYMBOLS.

In some cases, the syntax rules that apply to Unicode programs are different than those for non-Unicode programs. See Defining Types Using STRUCTURE.

Effect

Assigns any (internal) field string or structure to the field symbol from the ABAP Dictionary (s). All fields of the structure can be addressed by name: <fs>-fieldname. The structured field symbol points initially to the work area wa specified after DEFAULT.

The work area wa must be at least as long as the structure s. If s contains fields of the type I or F, wa should have the structure s or at least begin in that way, since otherwise alignment problems may occur.

Example

Address components of the flight bookings table SBOOK using a field symbol:

DATA SBOOK_WA LIKE SBOOK.

FIELD-SYMBOLS <SB> STRUCTURE SBOOK

DEFAULT SBOOK_WA.

...

WRITE: <SB>-BOOKID, <SB>-FLDATE.

ASSIGN, DATA

Additional help

Declaring Field Symbols

Reward points if useful

Regards

Anji

Re: field symbolsc code

dev_parbutteea — Fri, 25 May 2007 06:56:14 GMT

Hi,

ASSIGN text TO <f1>.

ASSIGN num TO <f2>.

DESCRIBE FIELD <f1> LENGTH <f2>.

WRITE: / <f1>, 'has length', num

if you had put <F2> instead of NUM ,

basically the output would have been :

Hello, how are you? has length 19

bcoz f1 contains 19 characters .

Re: field symbolsc code

Former Member — Fri, 25 May 2007 07:14:29 GMT

Hi,

Here are your answers referring your code -

1.

q1]] How does the "2" types of statements differentiates

i]ASSIGN <V> TO <FS>. Where <v > refers to any variable & <fs> to any field symbols

ii] MOVE <fs> TO <V>.

Answer: The basic difference between the MOVE & ASSIGN statements is as follows - In the MOVE statement, it is not possible to specify the field names dynamically as the contents of other fields. If you need to do this, you must use field symbols .

2.

q2]] How does the "NUM" variable's presence affect the output in the write statement----what I mean by the question is what would have happened if we had written <F2> instead of NUM ; min the following statements:-

ASSIGN text TO <f1>.

ASSIGN num TO <f2>.

DESCRIBE FIELD <f1> LENGTH <f2>.

WRITE: / <f1>, 'has length', num

Answer: Here the output would be same evenif you change the num to <f2>. The reason is that in the second line, you assigned the memory of num to <f2>. And in the third statement <f2> contains the output of describe field statement as length. So <f2> has value as length.

As <f2> is pointing to the memory location, address, of num and the value of num is same as the value contained in <f2>.

Hope this helps you.

PS If the answer solves your query, plz close the thread by rewarding each reply and marking it Solved.

Regards

Re: field symbolsc code

Former Member — Sat, 26 May 2007 07:24:10 GMT

the answers of Swapna Modi& Mr.Munogee are contradictory

Re: field symbolsc code

Former Member — Wed, 30 May 2007 06:32:16 GMT

Hi,

Kindly verify the results mentioned in the thread reply by trying it out practically. This will help you in understanding the thread reply responded correctly.

Hope this helps you.

PS As you verify, plz close the thread by marking it Sovled and rewarding the useful reply.

Regards

Message was edited by:

Sapna Modi

Re: field symbolsc code

Former Member — Sat, 09 Jun 2007 06:28:34 GMT

Sapna I had already rewarded the points did't you get them

Sujoy

Re: field symbolsc code

Former Member — Sat, 09 Jun 2007 06:29:13 GMT

Sapna I had already rewarded the points did't you get them pls let me know?

Sujoy

Re: field symbolsc code

Former Member — Sat, 09 Jun 2007 06:29:41 GMT

Sapna I had already rewarded the points did't you get them pls let me know?

Sujoy