Cの文字列のデータ構造
Data structure of C string
a = "abc"
a b c 0
b = "def"
a b c 0 d e f 0
a = a + b
a b c 0 d e f 0 a b c d e f 0
最初の“a b c 0”はゴミになる
First "abc" never reused