strtok()

char * strtok ( char * str, const char * delimiters );

Split string into tokens

A sequence of calls to this function split str into tokens, which are sequences of contiguous characters separated by any of the characters that are part of delimiters.

On a first call, the function expects a C string as argument for str, whose first character is used as the starting location to scan for tokens. In subsequent calls, the function expects a null pointer and uses the position right after the end of last token as the new starting location for scanning.
 a first call： ptr = strtok( str, " " );
In subsequent calls： ptr = strtok( NULL , " " );

/*************************************************
 * *
 * example of strtok() *
 * *
 * *
 * ************************************************/


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


int main()
{
     char str[] = "mao zhe dong";
     char *ptr;
     ptr = strtok( str, " " );
     puts( ptr );
     while( ptr != NULL )
     { printf( " The ptr pointer is at %d \n" , ptr-str+1 );
        ptr = strtok( NULL , " " );
        if(ptr != NULL) puts( ptr );//---------------
     }


      return 0;
}


输出：

mao
 The ptr pointer is at 1
zhe
 The ptr pointer is at 5
dong
 The ptr pointer is at 9


但语句：
if(ptr != NULL) puts( ptr );//---------------
中去掉 if(ptr != NULL)
则输出是：



mao
 The ptr pointer is at 1
zhe
 The ptr pointer is at 5
dong
 The ptr pointer is at 9
Segmentation fault (core dumped)


Segmentation fault (core dumped) 这一句不知为什么会出现，原因何在？



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