HIST_ENTRY结构中data域的使用出现在history.c文件中的replace_history_entry ()函数中。
而replace_history_entry ()函数在readline.c文件中有如下两处调用
char *
readline_internal (){…… if (entry && rl_undo_list) { char *temp = savestring (the_line); rl_revert_line (); entry = replace_history_entry (where_history (), the_line, (HIST_ENTRY *)NULL); free_history_entry (entry); strcpy (the_line, temp); free (temp); } }/* Perhaps put back the current line if it has changed. */maybe_replace_line (){ HIST_ENTRY *temp = current_history (); /* If the current line has changed, save the changes. */ if (temp && ((UNDO_LIST *)(temp->data) != rl_undo_list)) { temp = replace_history_entry (where_history (), the_line, rl_undo_list); free (temp->line); free (temp); }
}
下面是在[/root]# abcad —>[/root]# aabcad之后按下向上方向键时在replace_history_entry ()函数出被截获。
其中参数rl_undo_list的值为0x5d7cc。指向undo_list结构，下面是undo_list结构的定义(readline.h中)：
enum undo_code { UNDO_DELETE, UNDO_INSERT, UNDO_BEGIN, UNDO_END };/* What an element of THE_UNDO_LIST looks like. */typedef struct undo_list { struct undo_list *next; int start, end; /* Where the change took place. */ char *text; /* The text to insert, if undoing a delete. */ enum undo_code what; /* Delete, Insert, Begin, End. */} UNDO_LIST;/* The current undo list for RL_LINE_BUFFER. */extern UNDO_LIST *rl_undo_list;
rl_undo_list->next的值为0x5d78c
rl_undo_list->start的值为1
rl_undo_list->end的值为2
rl_undo_list->text的值为0既NULL
rl_undo_list->what的值为1既UNDO_INSERT
按下向下方向键，再按下向上方向键，
再次在previous_history ()函数下断点截获后发现data域不是0既NULL了。
这时是0x5d7cc，既是刚才的rl_undo_list的值！！！
幸福就是重复。每天跟自己喜欢的人一起，通电话，
