1.使用print命令查看变量值
使用print命令（简写为p）能够查看变量值。
使用例如以下的程序1进行測试。
#include(gdb) b main Breakpoint 1 at 0x804839a: file a.c, line 10. (gdb) r Starting program: /root/a.out Breakpoint 1, main () at a.c:10 10 head.index = 1; (gdb) n 11 head.next = NULL; (gdb) 14 for(i=0; i<3; i++){ (gdb) 15 head.index++; (gdb) 14 for(i=0; i<3; i++){ (gdb) p head $1 = {index = 2, next = 0x0} (gdb) n 15 head.index++; (gdb) 14 for(i=0; i<3; i++){ (gdb) 15 head.index++; (gdb) 14 for(i=0; i<3; i++){ (gdb) p head $3 = {index = 4, next = 0x0}struct node{ int index; struct node* next;};int main(void) { struct node head; head.index = 1; head.next = NULL; int i; for(i=0; i<3; i++){ head.index++; } return 0;}
print命令同意指定可选的格式，比如
p/x y
会以十六进制格式显示变量，而不是十进制。其它经常使用的格式为c（字符），s（字符串），f（浮点型）
2.使用display命令查看变量值
每次遇到断点，仅仅须要键入print命令就行查看变量值，可是，假设知道会在每次遇到断点时键入这个命令，那么使用
display命令（简写为disp）能节省很多其它的时间。这个命令要求GDB在运行每次有暂停时就输出指定条目。
使用上面的程序1输出的调试的结果例如以下：
(gdb) b main Breakpoint 1 at 0x804839a: file a.c, line 10. (gdb) b 15 Breakpoint 2 at 0x80483b1: file a.c, line 15. (gdb) r Starting program: /root/a.out Breakpoint 1, main () at a.c:10 10 head.index = 1; (gdb) disp head 1: head = {index = -1208168460, next = 0x80483d0} (gdb) c Continuing. Breakpoint 2, main () at a.c:15 15 head.index++; 1: head = {index = 1, next = 0x0} (gdb) Continuing. Breakpoint 2, main () at a.c:15 15 head.index++; 1: head = {index = 2, next = 0x0} (gdb) Continuing. Breakpoint 2, main () at a.c:15 15 head.index++; 1: head = {index = 3, next = 0x0} (gdb)
能够暂时禁用某个显示项，比如：
dis disp 1
暂时禁用显示列表中的条目1，条目能够通过 info disp命令检查。
要又一次启用条目，使用enable
enable disp 1
要全然删除条目，使用undisplay（简写为undisp）
undisp 1
3.使用call命令调用函数
使用call函数能够调用被调试程序的函数。
使用以下的程序2进行演示：
#includestruct node{ int index; char* content; struct node* next;};void display(struct node head){ printf("head.index=%d,head.content=%s\n",head.index,head.content);}int main(void) { struct node head; head.index = 1; head.content = "yes"; head.next = NULL; int i; for(i=0; i<3; i++){ head.index++; } display(head); return 0;}
(gdb) b main Breakpoint 1 at 0x80483f0: file a.c, line 15. (gdb) r Starting program: /root/a.out Breakpoint 1, main () at a.c:15 15 head.index = 1; (gdb) n 16 head.content = "yes"; (gdb) 17 head.next = NULL; (gdb) 20 for(i=0; i<3; i++){ (gdb) 21 head.index++; (gdb) call display(head) head.index=1,head.content=yes
4.使用ptype查看变量类型
使用程序2进行调试：
(gdb) b main Breakpoint 1 at 0x804842a: file a.c, line 16. (gdb) r Starting program: /root/a.out Breakpoint 1, main () at a.c:16 16 head.index = 1; (gdb) ptype head type = struct node { int index; char *content; struct node *next; } (gdb)
5.监视局部变量
使用info locals命令得到当前栈帧中全部局部变量的值列表。
使用程序2进行调试：
(gdb) b main Breakpoint 1 at 0x804842a: file a.c, line 16. (gdb) r Starting program: /root/a.out Breakpoint 1, main () at a.c:16 16 head.index = 1; (gdb) info locals head = {index = -1209402059, content = 0xb7ff0a50 "U\211\345WV1\366S\350N\212", next = 0x804849b} i = -1208168460 (gdb) n 17 head.content = "yes"; (gdb) 18 head.next = NULL; (gdb) 21 for(i=0; i<3; i++){ (gdb) info locals head = {index = 1, content = 0x8048574 "yes", next = 0x0} i = -1208168460 (gdb) n 22 head.index++; (gdb) info local head = {index = 1, content = 0x8048574 "yes", next = 0x0} i = 0 (gdb)
6.检查动态数组
对以下的程序3进行调试。
#include#include int main(void){ int a[3] = {1,2,3}; int *b = (int*)malloc(3*sizeof(int)); b[0] = 1; b[1] = 2; b[2] = 3; return 0;}
(gdb) b main Breakpoint 1 at 0x80483cd: file b.c, line 5. (gdb) r Starting program: /root/a.out Breakpoint 1, main () at b.c:5 5 int a[3] = {1,2,3}; (gdb) n 6 int *b = (int*)malloc(3*sizeof(int)); (gdb) 7 b[0] = 1; (gdb) 8 b[1] = 2; (gdb) 9 b[2] = 3; (gdb) 10 return 0; (gdb) p a $1 = {1, 2, 3} (gdb) p b $2 = (int *) 0x804b008 (gdb) p *b $3 = 1
假设是动态数组，直接使用p命令仅仅能打印一个数。
使用例如以下命令，能够打印出整个数组：
(gdb) p *b@3 $1 = {1, 2, 3}
(gdb)
语法例如以下：
p *pointer@number_of_elements.
还有一种方式是使用类型强制转换：
(gdb) p (int [3])*b $3 = {1, 2, 3} (gdb)
7.设置变量
在gdb中，值的设置很easy，比如
set x=12
会将x的当前值改动为12.
能够通过gdb的set args命令设置程序的命令行參数，该命令能够须要下次运行run命令时才会发生变化。事实上仅仅要在调用
gdb的run命令时使用新參数就能达到相同的效果。
gdb提供info args命令来检查当前函数的參数。
使用以下的程序4进行调试：
#include调试：void display(int i, char* argv){ printf("argv[%d]=%s\n",i,argv);}int main(int argc, char* argv[]){ int i; for (i=0; i
(gdb) set args 1 2 3 (gdb) b main Breakpoint 2 at 0x80483f0: file a.c, line 11. (gdb) b display Note: breakpoint 1 also set at pc 0x80483ca. Breakpoint 3 at 0x80483ca: file a.c, line 5. (gdb) r Starting program: /root/a.out 1 2 3 Breakpoint 2, main (argc=4, argv=0xbffff724) at a.c:11 11 for (i=0; i<argc; i++) { (gdb) info args argc = 4 argv = 0xbffff724 (gdb) c Continuing. Breakpoint 1, display (i=0, argv=0xbffff86a "/root/a.out") at a.c:5 5 printf("argv[%d]=%s\n",i,argv); (gdb) c Continuing. argv[0]=/root/a.out Breakpoint 1, display (i=1, argv=0xbffff876 "1") at a.c:5 5 printf("argv[%d]=%s\n",i,argv); (gdb) Continuing. argv[1]=1 Breakpoint 1, display (i=2, argv=0xbffff878 "2") at a.c:5 5 printf("argv[%d]=%s\n",i,argv); (gdb) Continuing. argv[2]=2 Breakpoint 1, display (i=3, argv=0xbffff87a "3") at a.c:5 5 printf("argv[%d]=%s\n",i,argv); (gdb) Continuing. argv[3]=3