How to understand the internal record format in mysql

[shengyun yao]

I want to know how the internal record fromat in mysql.

For example, in `int handler::write_row(uchar *buf)` function, I can get the value of one int field like this:
```
// i is the index num of the int field in field array
table->s->field->val_int();
```
Another way is get the value from buf like this:
```
ulong offset = (ulong)(field->ptr - table->record[0]);
table->s->field->val_int(buf + offset);
```
So, what are the difference and what situation is the two methods used in? Besides, I can see `uchar *record[2]; `in class `TABLE`. So what is the relation between record and the `buf` in `int handler::write_row(uchar *buf)` (I guess `record[0]` is the same with `buf`, am I right?). And what is the relation between `record[0]` and `record[1]`.

Anybody help me?