ANSI/POSIC 函数strtok

sybaselu

Test case 1:

1. 
   
2. #include <stdio.h>
   
3. #include <string.h>
   
4. 
   
5. int main ()
   
6. {
   
7.   char str[] ="This is a sample string, just testing.";
   
8.   char * pch;
   
9.   printf ("Splitting string "%s" in tokens:\n",str);
   
10.   pch = strtok (str,",");   //精确定义一个截断符","
    
11.   while (pch != NULL)
    
12.   {
    
13.     printf ("%s\n",pch);
    
14.     pch = strtok (NULL, " ");
    
15.   }
    
16.   return 0;
    
17. }
    

复制代码

Result :

1. 
   
2. [root@root ANSI]# ./a.out
   
3. Splitting string "This is a sample string, just testing." in tokens:
   
4. This is a sample string
   
5. just
   
6. testing.
   
7. [root@root ANSI]#
   

复制代码

Test case 2:

1. 
   
2. #include <stdio.h>
   
3. #include <string.h>
   
4. 
   
5. int main ()
   
6. {
   
7.   char str[] ="This is a sample string, just testing.";
   
8.   char * pch;
   
9.   printf ("Splitting string "%s" in tokens:\n",str);
   
10.   pch = strtok (str," ,");  //截断符","前面加上一个空格
    
11.   while (pch != NULL)
    
12.   {
    
13.     printf ("%s\n",pch);
    
14.     pch = strtok (NULL, " ");
    
15.   }
    
16.   return 0;
    
17. }
    

复制代码

Result：

1. 
   
2. [root@root ANSI]# ./a.out
   
3. Splitting string "This is a sample string, just testing." in tokens:
   
4. This
   
5. is
   
6. a
   
7. sample
   
8. string,
   
9. just
   
10. testing.
    
11. [root@root ANSI]#
    

复制代码

例2中为什么没有用","作为截断符呢？

ralph_cheng

manpage里说了
strtok()的第二个参数是截断符集合，也就是说字符串里的每一个字符都是截断符

默难

1 LZ的问题可以man strtok
2 是POSIX，不是POSIC……

sybaselu

Post by ralph_cheng
manpage里说了
strtok()的第二个参数是截断符集合，也就是说字符串里的每一个字符都是截断符

如果说是以字符串中的每个字符为一个截断字符集， 那么上面的输出为什么还有:
string,
这样的输出呢？ 截断字符","肯定不会在出现的。

zlbruce

1. #include <stdio.h>
2. #include <string.h>
4. int main ()
5. {
6.   char str[] ="This is a sample string, just testing.";
7.   char * pch;
8.   printf ("Splitting string "%s" in tokens:\n",str);
9.   pch = strtok (str," ,");  //截断符","前面加上一个空格
10.   while (pch != NULL)
11.   {
12.     printf ("%s\n",pch);
13.     [color=red]pch = strtok (NULL, " ");[/color]==>pch = strtok (NULL, " ,");
14.   }
15.   return 0;
16. }

复制代码

ralph_cheng

Post by sybaselu
如果说是以字符串中的每个字符为一个截断字符集， 那么上面的输出为什么还有:
string,
这样的输出呢？ 截断字符","肯定不会在出现的。

Before the while loop starts, str is splited into "This" and "is a ..." since the  " " between "This" and "is a ..." is a delimiter.

In the loop, "," is no longer a delimiter only " " is considered as a delimitor. Thats why "string," shows up.

sybaselu

对于zlbruse:
  我的意思并不是要用","作为截断符，而是想知道在第一次调用strtok时为什么不用参数中多个字符作为截断符集，而只是以" "作为截断符，忽略了","。
To strong man ralph_cheng:
Tks, Owe, I dont't  think that I maybe obtain a little  hits from your complaintation. but I seem still be stuck in wh

at  your a bit puzzle saying. Well, since strtok() be called at first, the pointer pch pointed the return character of

strtok, that is , an character of "T..", becase the secnod parameter as "" , then the delimiter "." be omited. after e

ntring the loop, we have made the second calling of strtok() , so the delimiter "," no longer in the set of delimiter.

right?

ralph_cheng

Post by sybaselu
对于zlbruse:
  我的意思并不是要用","作为截断符，而是想知道在第一次调用strtok时为什么不用参数中多个字符作为截断符集，而只是以" "作为截断符，忽略了","。
To strong man ralph_cheng:
Tks, Owe, I dont't  think that I maybe obtain a little  hits from your complaintation. but I seem still be stuck in wh

at  your a bit puzzle saying. Well, since strtok() be called at first, the pointer pch pointed the return character of

strtok, that is , an character of "T..", becase the secnod parameter as "" , then the delimiter "." be omited. after e

ntring the loop, we have made the second calling of strtok() , so the delimiter "," no longer in the set of delimiter.

right?

在你的有问题的那个程序里，
第一个调用strtok是在while loop之前，截断符为空格和逗号，这次调用返回了第一个token，也就是"This"，它被一个空格截断。
然后就开始while loop了，在loop里的strtok就不再把逗号当作截断符，而只把空格当作截断符（因为你是这样写的），所以逗号会出现在token里。