struct instruction

1.1 struct instruction

An instruction has the following structure:

struct instruction {
        int instr_type;
        union {
                char *lbl;
                struct mnemonic *mnm;
                struct directive *dir;
        } u;
        struct instruction *next;
};

instr_type

This member specifies the type of the instruction. Table 1.1 shows its values.

u

This member represents for one specific type of instruction. It can be a label definition, or a mnemonic (real or synthetic instruction), or a directive (pseudo-operation). Therefore, it is a union of three pointers, one to a string of label name, one to a mnemonic structure (see section 1.2), and the other to a directive structure (see section 1.6). Which member is active depends on the value of instr_type. Table 1.1 shows the rule.

next

This memeber points to the next instruction in the list.

Table 1.1 Instruction Types

Name	Value	Active Member in Union	Instruction Data Structure
`LBL`	`0`	`u.lbl`	`a string of label name`
`MNM`	`1`	`u.mnm`	`a mnemonic structure`
`DIR`	`2`	`u.dir`	`a directive structure`

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