Thread: strange behaviour of sscanf

If that's an exact copy of your code and not some poor attempt at abbreviation so that we can "find the problem more easily", then buf doesn't point to any memory that you own, so the behavior is undefined and your working with garbage. Otherwise, you've introduced several bugs and I suggest that you post your code exactly.

scanf() and parsing strings can be tricky business. Typically the issue arrises when when you call something a string and scanf() wants to call it a number. But even at that, its not scanf() doing something wrong as much as you are wanting it to work outside its default behavior. Thats the typical downfall of the scanf() functions. The other common issue with scanf() is when it handles white space in a manner that is unexpected. As for your code, I don't see where the common "my scanf() function is failing" type scenarios:

Code:

if(sscanf(buf, "%*s %s %s", path, alias)!=2)
{
    ErrorOut(ERR_WRONGPAR);
}

Do go ahead and explain this part for me.

actually this is the function:

PHP Code:

int ExecOrder(char *buf, int acceptfd)
{
       char *order;
       sscanf(buf, "%s ", order);
       if(strcoll(order, "PATH")==0)
       {
               char *path, *alias;
               int Path;
               printf("Buf: %s \n", buf);
               if(sscanf(buf, "%*s %s %s", path, alias)!=2)
               {
                       ErrorOut(ERR_WRONGPAR); 
               }
               printf("Buf: %s \n",buf);
               printf("Path: %s\nAlias: %s\n", path, alias);
               if(strcoll(path, "U")==0)
               {
                       Path = 0x04;
               }else if(strcoll(path, "IP")==0)
               {
                       Path = 0x10;
               }else if(strcoll(path, "I")==0)
               {
                       Path = 0x08;
               }else
               {
                       ErrorOut(ERR_WRONGPAR);
               }
               if(strcoll(alias, "ON")==0)
               {
                       Path = Path || 0x80;
               }else if(strcoll(alias, "OFF")==0)
               {
                       Path = Path && 0x79;
               }else
               {
                       ErrorOut(ERR_WRONGPAR); 
               }
 
              SetPath(Path);

               msg="OK";

               len = strlen(msg);

                bytes_sent = send(acceptfd, msg, len, 0);
               close(acceptfd);
               return 0;
       }else if(strcoll(order, "RANGE")==0)
       {
               char *range;
               if(sscanf(buf, "%s %s", order, range)!=2)
               {
                       ErrorOut(ERR_WRONGPAR);
               }

               if(strcoll(range, "20A")==0)
               {
                       SetRANGE(0xc1);

               }else if(strcoll(range, "10A")==0)
               {
                       SetRANGE(0xc2);

               }else if(strcoll(range, "1A")==0)
               {
                       SetRANGE(0xc3);

               }else if(strcoll(range, "100mA")==0)
               {
                       SetRANGE(0xc4);

               }else if(strcoll(range, "10mA")==0)
               {
                       SetRANGE(0xc5);

               }else if(strcoll(range, "1mA")==0)
               {
                       SetRANGE(0xc6);
               }else
               {
                       ErrorOut(ERR_WRONGPAR);
               }

               msg="OK";
               len = strlen(msg);
               bytes_sent = send(acceptfd, msg, len, 0);
               close(acceptfd);
               return 0;
       }
       ErrorOut(ERR_UNKNOWNCMD);

} 


the strange thing is, that the range part is working perfectly, while the path is making that problems.
I really appreciate that you try to help me, thanks.

>..is still wrong.
How so? Both path and alias are pointers to char (albeit, uninitialized pointers, but your correction suggests the format modifier is the problem). What the sscanf call does is read and discard one word (notice the asterisk modifier), then read another word and copy it to path, and read another word and copy it to alias. On a successful call, 2 will be returned because only 2 items were copied. The only real problem at this point is path and alias pointing into limbo, and of course, the lack of field widths producing a gets-like overflow risk.