初学GDB(2)
作者：互联网
搬运自我的CSDN https://blog.csdn.net/u013213111/article/details/88096937
以The C Programming Language中1.9节的程序为例，试用了以下命令：
1.backtrace，简写bt，查看函数调用的顺序（函数调用栈的信息）；
2.frame N，切换到栈编号为N的上下文中；
3.info frame，简写info f，查看当前函数调用的栈帧信息 ；
4.info locals，查看当前局部变量的值；
5.info args，查看当前函数参数的值；
6.set pagination off，关闭分页显示；
7.l 1,50，显示程序的第1-50行；
注意main()中调用getlines的时候实参是line和MAXLINE，getlines的形参是s和lim，在16行的断点处查看line的地址，为0xbfffe7bc，在第29行的断点处发现s=0xbfffe7bc，两者一致，说明了把数组名作为参数时，传递给函数的是数组起始元素的地址，所以getlines中对s进行修改也就是对main中的line进行修改，而无需特地返回一个修改后的数组。MAXLINE是宏，暂时无法直接查看，似乎在用gcc时要设置其他参数才可。
记录如下：
1 xxx@xxx-VirtualBox:~/test$ gdb 1-9 -q
2 Reading symbols from 1-9...done.
3 (gdb) set pagination off
4 (gdb) l 1,50
5 1 #include <stdio.h>
6 2
7 3 #define MAXLINE 1000
8 4
9 5 int getlines(char line[], int maxline);
10 6 void copy(char to[], char from[]);
11 7
12 8 int main()
13 9 {
14 10 int len;
15 11 int max;
16 12 char line[MAXLINE];
17 13 char longest[MAXLINE];
18 14
19 15 max = 0;
20 16 while ((len = getlines(line, MAXLINE)) > 0)
21 17 if (len > max) {
22 18 max = len;
23 19 copy(longest, line);
24 20 }
25 21 if (max > 0)
26 22 printf("%s", longest);
27 23 return 0;
28 24 }
29 25
30 26 int getlines(char s[], int lim)
31 27 {
32 28 int c, i;
33 29 for (i = 0; i < lim-1 && (c = getchar()) != EOF && c != '\n'; ++i)
34 30 s[i] = c;
35 31 if (c == '\n') {
36 32 s[i] = c;
37 33 ++i;
38 34 }
39 35 s[i] = '\0';
40 36 return i;
41 37 }
42 38
43 39 void copy(char to[], char from[])
44 40 {
45 41 int i;
46 42 i = 0;
47 43 while ((to[i] = from[i]) != '\0')
48 44 ++i;
49 45 }
50 (gdb) b 16
51 Breakpoint 1 at 0x80484c4: file 1-9.c, line 16.
52 (gdb) b 29
53 Breakpoint 2 at 0x8048563: file 1-9.c, line 29.
54 (gdb) b 43
55 Breakpoint 3 at 0x80485d0: file 1-9.c, line 43.
56 (gdb) r
57 Starting program: /home/ant/test/1-9
58
59 Breakpoint 1, main () at 1-9.c:16
60 16 while ((len = getlines(line, MAXLINE)) > 0)
61 (gdb) p &line
62 $1 = (char (*)[1000]) 0xbfffe7bc
63 (gdb) info f
64 Stack level 0, frame at 0xbfffefb0:
65 eip = 0x80484c4 in main (1-9.c:16); saved eip = 0xb7e1e637
66 source language c.
67 Arglist at 0xbfffef98, args:
68 Locals at 0xbfffef98, Previous frame's sp is 0xbfffefb0
69 Saved registers:
70 ebp at 0xbfffef98, eip at 0xbfffefac
71 (gdb) c
72 Continuing.
73
74 Breakpoint 2, getlines (s=0xbfffe7bc "", lim=1000) at 1-9.c:29
75 29 for (i = 0; i < lim-1 && (c = getchar()) != EOF && c != '\n'; ++i)
76 (gdb) bt
77 #0 getlines (s=0xbfffe7bc "", lim=1000) at 1-9.c:29
78 #1 0x0804850d in main () at 1-9.c:16
79 (gdb) frame 0
80 #0 getlines (s=0xbfffe7bc "", lim=1000) at 1-9.c:29
81 29 for (i = 0; i < lim-1 && (c = getchar()) != EOF && c != '\n'; ++i)
82 (gdb) info locals
83 c = 0
84 i = 0
85 (gdb) frame 1
86 #1 0x0804850d in main () at 1-9.c:16
87 16 while ((len = getlines(line, MAXLINE)) > 0)
88 (gdb) info locals
89 len = 0
90 max = 0
91 line = '\000' <repeats 65 times>, "\360\377\267\000\000\000\000\000\000\000\000\251\071\377\267\000\220\373\267\000\220\373\267\260Q\375\267(\352\377\277\270\022\376\267\000\220\373\267\034*\000\000\003\000\000\000\062\000\000\000\377\377\377\377\000\000\000\000,\001\000\000A\a\376\267\000\000\000\000\000\000\033\000\\\361\032\000\\\361\032\000\000\000\000\000\005\000\000\000\000\000\033\000\000\060\033\000\324.\033\000\034Z\033\000\000\360\032\000\003", '\000' <repeats 31 times>...
92 longest = "P\345td\214P\026\000\214P\026\000\214P\026\000\234a\000\000\234a\000\000\004\000\000\000\004\000\000\000Q\345td", '\000' <repeats 20 times>, "\006\000\000\000\020\000\000\000R\345tdi2\376\267h\356\377\277\260}\373\267͒ᷘ\356\377\277\222\177\376\267", '\000' <repeats 12 times>, "\003\000\000\000GNU\000\335Q\222\247\000\000\000\000\004\243\376\267h\356\377\277\000\000\000\000u\272\375\267`?\376\267\345\222\341\267\067\266\375\267\000\000\000\000X\370\377\267\000\000\000\000d\356\377\277`\356\377\277\020ii\r\000\002\000\000d\356\377\277\071>\376\267\244\201\340\267\016\002\000\000\260Q\375\267\307\016\340==F\376"...
93 (gdb) frame 0
94 #0 getlines (s=0xbfffe7bc "", lim=1000) at 1-9.c:29
95 29 for (i = 0; i < lim-1 && (c = getchar()) != EOF && c != '\n'; ++i)
96 (gdb) c
97 Continuing.
98 ab
99
100 Breakpoint 3, copy (to=0xbfffeba4 "P\345td\214P\026", from=0xbfffe7bc "ab\n") at 1-9.c:43
101 43 while ((to[i] = from[i]) != '\0')
102 (gdb) bt
103 #0 copy (to=0xbfffeba4 "P\345td\214P\026", from=0xbfffe7bc "ab\n") at 1-9.c:43
104 #1 0x080484f6 in main () at 1-9.c:19
105 (gdb) info locals
106 i = 0
107 (gdb) n
108 44 ++i;
109 (gdb) n
110 43 while ((to[i] = from[i]) != '\0')
111 (gdb) p to
112 $2 = 0xbfffeba4 "a\345td\214P\026"
113 (gdb) c
114 Continuing.
115
116 Breakpoint 2, getlines (s=0xbfffe7bc "ab\n", lim=1000) at 1-9.c:29
117 29 for (i = 0; i < lim-1 && (c = getchar()) != EOF && c != '\n'; ++i)
118 (gdb) Quit
标签：gdb,000,29,GDB,初学,267,line,377 来源： https://www.cnblogs.com/lyrich/p/10500960.html