swap变量交换&&递归调用栈帧
(lldb) po a
0x00007ffeefbff60c
(lldb) po b
0x00007ffeefbff608
(lldb) p a
(int *) $2 = 0x00007ffeefbff60c
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = step over
* frame #0: 0x0000000100000f3a 1`swap(a=0x00007ffeefbff60c, b=0x00007ffeefbff608) at main.cpp:8
frame #1: 0x0000000100000f63 1`main at main.cpp:13
frame #2: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) p b
(int *) $3 = 0x00007ffeefbff608
(lldb) p t
(int) $4 = 3
(lldb) p *a
(int) $5 = 4
(lldb) p *b
(int) $6 = 3
(lldb) up
frame #1: 0x0000000100000f63 1`main at main.cpp:13
10 {
11 int a,b;
12 a = 3, b = 4;
-> 13 [4ms[0mwap(&a,&b);
14 printf("%d %d\n",a,b);
15 }
(lldb) p a
(int) $7 = 4
(lldb) p b
(int) $8 = 3
(lldb) p &a
(int *) $9 = 0x00007ffeefbff60c
(lldb) p &b
(int *) $10 = 0x00007ffeefbff608
(lldb) q
Program ended with exit code: 9
如果第三个变量改成int *t;
但却错了，原来是*t只读的，内存地址“0”不能写。
还有一种是交换了地址，但是没有修改它们指向的内容。
指向函数的指针，万能的指针const void *，可以强制转换成任意类型的指针。
排序的对象是整型数组。
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x0000000100000f2b 1`f(n=3) at main.cpp:4
frame #1: 0x0000000100000f72 1`main at main.cpp:8
frame #2: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) up
frame #1: 0x0000000100000f72 1`main at main.cpp:8
5 }
6 int main()
7 {
-> 8 printf("%d\n",[4mf[0m(3));
9 }
(lldb) p f
(int (*)(int)) $0 = 0x0000000100000f20 (1`f(int) at main.cpp:3)
(lldb) s
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x0000000100000f2b 1`f(n=2) at main.cpp:4
frame #1: 0x0000000100000f4f 1`f(n=3) at main.cpp:4
frame #2: 0x0000000100000f72 1`main at main.cpp:8
frame #3: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) s
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x0000000100000f2b 1`f(n=1) at main.cpp:4
frame #1: 0x0000000100000f4f 1`f(n=2) at main.cpp:4
frame #2: 0x0000000100000f4f 1`f(n=3) at main.cpp:4
frame #3: 0x0000000100000f72 1`main at main.cpp:8
frame #4: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) s
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
* frame #0: 0x0000000100000f2b 1`f(n=0) at main.cpp:4
frame #1: 0x0000000100000f4f 1`f(n=1) at main.cpp:4
frame #2: 0x0000000100000f4f 1`f(n=2) at main.cpp:4
frame #3: 0x0000000100000f4f 1`f(n=3) at main.cpp:4
frame #4: 0x0000000100000f72 1`main at main.cpp:8
frame #5: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) s
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = step in
* frame #0: 0x0000000100000f4f 1`f(n=1) at main.cpp:4
frame #1: 0x0000000100000f4f 1`f(n=2) at main.cpp:4
frame #2: 0x0000000100000f4f 1`f(n=3) at main.cpp:4
frame #3: 0x0000000100000f72 1`main at main.cpp:8
frame #4: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) s
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = step in
* frame #0: 0x0000000100000f4f 1`f(n=2) at main.cpp:4
frame #1: 0x0000000100000f4f 1`f(n=3) at main.cpp:4
frame #2: 0x0000000100000f72 1`main at main.cpp:8
frame #3: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) s
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = step in
* frame #0: 0x0000000100000f4f 1`f(n=3) at main.cpp:4
frame #1: 0x0000000100000f72 1`main at main.cpp:8
frame #2: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) s
(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = step in
* frame #0: 0x0000000100000f72 1`main at main.cpp:8
frame #1: 0x00007fff7018d015 libdyld.dylib`start + 1
(lldb) s
6
(lldb)
