C strtok

CSE:~/test # cat strtok.c
#include <stdio.h>
#include <string.h>

int main(void)
{
char str[] = "root:x:0:root:/root:/bin/sh:";
char *token;
token = strtok(str,":");
printf("%s\n",token);
while ((token = strtok(NULL,":")) != NULL)
printf("%s\n",token);
return 0;
}
CSE:~/test # ./strtok
root
x
0
root
/root
/bin/sh

第一次调用时把字符串传给strtok，以后每次调用时第一个参数只要传NULL就可以了，strtok函数自己会记住上次处理到字符串的什么位置（显然这是通过strtok函数中的一个静态指针变量记住的）

(gdb) start
Temporary breakpoint 1 at 0x400594: file strtok.c, line 6.
Starting program: /root/test/strtok
Missing separate debuginfo for /lib64/ld-linux-x86-64.so.2
Try: zypper install -C "debuginfo(build-id)=c1807b5762068e6c5f4a6a0ed48d9d4469965351"
Missing separate debuginfo for /lib64/libc.so.6
Try: zypper install -C "debuginfo(build-id)=74ef01bbffa60bc29e6768832b775b13c191a60b"

Temporary breakpoint 1, main () at strtok.c:6
6       char str[] = "root:x:0:root:/root:/bin/sh:";
(gdb) n
8       token = strtok(str,":");
(gdb) display str
1: str = "root:x:0:root:/root:/bin/sh:"
(gdb) n
9       printf("%s\n",token);
1: str = "root\000x:0:root:/root:/bin/sh:"
(gdb)
root
10 while ((token = strtok(NULL,":")) != NULL)
1: str = "root\000x:0:root:/root:/bin/sh:"
(gdb)
11      printf("%s\n",token);
1: str = "root\000x\000\060:root:/root:/bin/sh:"
(gdb)
x
10 while ((token = strtok(NULL,":")) != NULL)
1: str = "root\000x\000\060:root:/root:/bin/sh:"
(gdb)
11      printf("%s\n",token);
1: str = "root\000x\000\060\000root:/root:/bin/sh:"
(gdb)