我很好奇，所以这里有一个例子程序：

#include <stdio.h>
#include <stdlib.h>

struct foo {
    int bar;
};

int main() {
    struct foo *foo = malloc(sizeof *foo);
    foo->bar = 42;
    printf("bar=%d\n", foo->bar);
    foo->bar = 1;
    printf("bar=%d\n", foo->bar);
    free(foo);
}

字符串
和一个使用watch的gdb会话：

(gdb) start
Temporary breakpoint 1 at 0x1161: file 1.c, line 9.
Starting program: /home/allan/a.out 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Temporary breakpoint 1, main () at 1.c:9
9               struct foo *foo = malloc(sizeof *foo);
(gdb) watch foo->bar
Hardware watchpoint 2: foo->bar
(gdb) c
Continuing.

Hardware watchpoint 2: foo->bar

Old value = -134434816
New value = 0
main () at 1.c:10
10              foo->bar = 42;
(gdb) c
Continuing.

Hardware watchpoint 2: foo->bar

Old value = 0
New value = 42
main () at 1.c:11
11              printf("bar=%d\n", foo->bar);
(gdb) c
Continuing.
bar=42

Hardware watchpoint 2: foo->bar

Old value = 42
New value = 1
main () at 1.c:13
13              printf("bar=%d\n", foo->bar);
(gdb) c
Continuing.
bar=1

Hardware watchpoint 2: foo->bar

Old value = 1
New value = 1431655769

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