strtok的用法，code不工作 [英] Strtok usage, code not working

问题描述

我想使用的strtok（）。以下是我写的一张code的。它不工作，但打印，无限。

I am trying to use strtok(). Following is the piece of code that I wrote. It does not work but prints ", '" infinitely.

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

int main(){
char str[]="this, by the way, is a 'sample'";
char *tokens;
tokens = strtok(str, ", '");
//printf("%s\n",tokens);
//printf("%s\n", str);
while(tokens!=NULL)
{
    printf("%s\n", tokens);
    tokens = (NULL, ", '");
}
return 0;
}

以下是从的strtok（）手册页，这工作完全正常的code。

Following is the code from a strtok() manual page, which works perfectly fine.

#include <stdio.h>
#include <string.h>

int main ()
{
  char str[] ="- This, a sample string.";
  char * pch;
  printf ("Splitting string \"%s\" into tokens:\n",str);
  pch = strtok (str," ,.-");
  while (pch != NULL)
  {
    printf ("%s\n",pch);
    pch = strtok (NULL, " ,.-");
  }
  return 0;
}

我觉得我也做了同样的事情。在我的code不能找出故障。可能有人请指出。

I feel I have done the exact same thing. Can't figure out the fault in my code. Could someone please point out.

推荐答案

有趣的错误！你忘了函数名。注意里面而环体下面的前pression：

Interesting bug! You forgot function name. Notice inside while-loop body following expression:

tokens =  (NULL, ",'");
         ^ 
          'strtok' missing 

应该是：

tokens = strtok(NULL, ",'");

有趣的是，这是不会编译错误，事实​​上：

tokens = (NULL, ",'");

是一个有效的前pression这等于：

is a valid expression which is equals to:

tokens = ",'";

（注： NULL 有没有副作用）

阅读：逗号操作：，

逗号操作符，的左到右联。两位前pressions
  用逗号分隔的是从左向右。左操作数
  始终评估，所有副作用的权前完成
  操作数评估。

The comma operator , has left-to-right associativity. Two expressions separated by a comma are evaluated left to right. The left operand is always evaluated, and all side effects are completed before the right operand is evaluated.

由于括号（ ）在 = 评估后，运算符的右手操作数，分配给标记。而由于标记从来没有分配 NULL 所以而（令牌！= NULL）从来没有打破，这就是你得到，无限的原因！

Due to parenthesis ( ) at rhs of =, after evaluating , operator right hand operand "," is assigned to token. And because token never assigned NULL so while(tokens != NULL) never breaks, and this is the reason that you are getting "," infinitely!

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