打印大数组中的内容
int main()
{
int array[201];
int i;
for (i = 0; i < 201; i++)
array[i] = i;
return 0;
}
在gdb中，如果要打印大数组的内容，缺省最多会显示200个元素：
(gdb) p array
$1 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94,
95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132,
133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169,
170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199...}
- 可以使用如下命令，设置这个最大限制数：
(gdb) set print elements number-of-elements
- 也可以使用如下命令，设置为没有限制：
(gdb) set print elements 0
或者
(gdb) set print elements unlimited
打印数组中任意连续元素值
在gdb中，如果要打印数组中任意连续元素的值，可以使用p array[index]@num命令（p是print命令的缩写）。其中index是数组索引（从0开始计数），num是连续多少个元素。以上面代码为例：
(gdb) p array
$8 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62,
63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93,
94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119,
120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144,
145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169,
170, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 190, 191, 192, 193, 194,
195, 196, 197, 198, 199...}
(gdb) p array[60]@10
$9 = {60, 61, 62, 63, 64, 65, 66, 67, 68, 69}
可以看到打印了array数组第60~69个元素的值。
如果要打印从数组开头连续元素的值，也可使用这个命令：p *array@num：
(gdb) p *array@10
$2 = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
打印静态变量的值
/* main.c */
extern void print_var_1(void);
extern void print_var_2(void);
int main(void)
{
print_var_1();
print_var_2();
return 0;
}
/* static-1.c */
#include <stdio.h>
static int var = 1;
void print_var_1(void)
{
printf("var = %d\n", var);
}
/* static-2.c */
#include <stdio.h>
static int var = 2;
void print_var_2(void)
{
printf("var = %d\n", var);
}
在gdb中，如果直接打印静态变量，则结果并不一定是你想要的：
$ gcc -g main.c static-1.c static-2.c
$ gdb -q ./a.out
(gdb) start
(gdb) p var
$1 = 2
$ gcc -g main.c static-2.c static-1.c
$ gdb -q ./a.out
(gdb) start
(gdb) p var
$1 = 1
你可以显式地指定文件名（上下文）：
(gdb) p 'static-1.c'::var
$1 = 1
(gdb) p 'static-2.c'::var
$2 = 2
每行打印一个结构体成员
#include <stdio.h>
#include <pthread.h>
typedef struct
{
int a;
int b;
int c;
int d;
pthread_mutex_t mutex;
}ex_st;
int main(void) {
ex_st st = {1, 2, 3, 4, PTHREAD_MUTEX_INITIALIZER};
printf("%d,%d,%d,%d\n", st.a, st.b, st.c, st.d);
return 0;
}
默认情况下，gdb以一种“紧凑”的方式打印结构体。以上面代码为例：
(gdb) n
15 printf("%d,%d,%d,%d\n", st.a, st.b, st.c, st.d);
(gdb) p st
$1 = {a = 1, b = 2, c = 3, d = 4, mutex = {__data = {__lock = 0, __count = 0, __owner = 0, __nusers = 0, __kind = 0,
__spins = 0, __list = {__prev = 0x0, __next = 0x0}}, __size = '\000' <repeats 39 times>, __align = 0}}
可以看到结构体的显示很混乱，尤其是结构体里还嵌套着其它结构体时。
可以执行“set print pretty on”命令，这样每行只会显示结构体的一名成员，而且还会根据成员的定义层次进行缩进：
(gdb) set print pretty on
(gdb) p st
$2 = {
a = 1,
b = 2,
c = 3,
d = 4,
mutex = {
__data = {
__lock = 0,
__count = 0,
__owner = 0,
__nusers = 0,
__kind = 0,
__spins = 0,
__list = {
__prev = 0x0,
__next = 0x0
}
},
__size = '\000' <repeats 39 times>,
__align = 0
}
}
打印变量的类型和所在文件
#include <stdio.h>
struct child {
char name[10];
enum { boy, girl } gender;
};
struct child he = { "Tom", boy };
int main (void)
{
static struct child she = { "Jerry", girl };
printf ("Hello %s %s.\n", he.gender == boy ? "boy" : "girl", he.name);
printf ("Hello %s %s.\n", she.gender == boy ? "boy" : "girl", she.name);
return 0;
}
在gdb中，可以使用如下命令查看变量的类型：
(gdb) whatis he
type = struct child
如果想查看详细的类型信息：
(gdb) ptype he
type = struct child {
char name[10];
enum {boy, girl} gender;
}
如果想查看定义该变量的文件：
(gdb) i variables he
All variables matching regular expression "he":
File variable.c:
struct child he;
Non-debugging symbols:
0x0000000000402030 she
0x00007ffff7dd3380 __check_rhosts_file
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