Forward Reference Problem and Future Symbol Problem in 8086

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Forward Reference Problem and Future Symbol Problem in 8086


Forward Reference Problem

A typical line in a program could be

BEGIN:MOV AX,SUM 

In this example BEGIN is a label which corresponds to the address that line of code is stored.A label when defined is called symbol.There will be a memory address corresponding to all symbols.

 All current assemblers allow the use of labels rather than numeric addresses of memory locations.However finally the labels must be translated to memory addresses.As such an important issue that an assembler will have to sort out what is called Forward Reference Problem

Future Symbol Problem

take a look at this code

BEGIN: MOV AX,BX
               JMP AGAIN
               ......................
               ......................
               ......................  
               ......................
 AGAIN:.....................

in the second line the assembler encounters a problem that AGAIN label is undefined.The assembler has no knowlege of it,but the value of the symbol AGAIN is needed before it can be defined .It is called Future Symbol Problem
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